Chapter 1. Air Navigation
Section 1. Navigation
a. Various types
of air navigation aids are in use today, each serving a special purpose. These
aids have varied owners and operators, namely: the Federal Aviation
Administration (FAA), the military services, private organizations, individual
states and foreign governments. The FAA has the statutory authority to
establish, operate, maintain air navigation facilities and to prescribe
standards for the operation of any of these aids which are used for instrument
flight in federally controlled airspace. These aids are tabulated in the
Airport/Facility Directory (A/FD).
b. Pilots should
be aware of the possibility of momentary erroneous indications on cockpit
displays when the primary signal generator for a ground-based navigational
transmitter (for example, a glideslope, VOR, or nondirectional beacon) is
inoperative. Pilots should disregard any navigation indication, regardless of
its apparent validity, if the particular transmitter was identified by NOTAM or
otherwise as unusable or inoperative.
Radio Beacon (NDB)
a. A low or medium
frequency radio beacon transmits nondirectional signals whereby the pilot of an
aircraft properly equipped can determine bearings and “home” on the station.
These facilities normally operate in a frequency band of 190 to 535 kilohertz
(kHz), according to ICAO Annex 10 the frequency range for NDBs is between 190
and 1750 kHz, and transmit a continuous carrier with either 400 or 1020 hertz
(Hz) modulation. All radio beacons except the compass locators transmit a
continuous three-letter identification in code except during voice
b. When a radio
beacon is used in conjunction with the Instrument Landing System markers, it is
called a Compass Locator.
transmissions are made on radio beacons unless the letter “W” (without voice) is
included in the class designator (HW).
d. Radio beacons
are subject to disturbances that may result in erroneous bearing information.
Such disturbances result from such factors as lightning, precipitation static,
etc. At night, radio beacons are vulnerable to interference from distant
stations. Nearly all disturbances which affect the Automatic Direction Finder
(ADF) bearing also affect the facility's identification. Noisy identification
usually occurs when the ADF needle is erratic. Voice, music or erroneous
identification may be heard when a steady false bearing is being displayed.
Since ADF receivers do not have a “flag” to warn the pilot when erroneous
bearing information is being displayed, the pilot should continuously monitor
the NDB's identification.
Omni-directional Range (VOR)
a. VORs operate
within the 108.0 to 117.95 MHz frequency band and have a power output necessary
to provide coverage within their assigned operational service volume. They are
subject to line-of-sight restrictions, and the range varies proportionally to
the altitude of the receiving equipment.
Normal service ranges for the various classes of VORs are given in Navigational
Aid (NAVAID) Service Volumes, Paragraph 1-1-8.
b. Most VORs are
equipped for voice transmission on the VOR frequency. VORs without voice
capability are indicated by the letter “W” (without voice) included in the class
c. The only
positive method of identifying a VOR is by its Morse Code identification or by
the recorded automatic voice identification which is always indicated by use of
the word “VOR” following the range's name. Reliance on determining the
identification of an omnirange should never be placed on listening to voice
transmissions by the Flight Service Station (FSS) (or approach control facility)
involved. Many FSSs remotely operate several omniranges with different names. In
some cases, none of the VORs have the name of the “parent” FSS. During periods
of maintenance, the facility may radiate a T-E-S-T code (- D DDD -) or the code
may be removed. Some VOR equipment decodes the identifier and displays it to the
pilot for verification to charts, while other equipment simply displays the
expected identifier from a database to aid in verification to the audio tones.
You should be familiar with your equipment and use it appropriately. If your
equipment automatically decodes the identifier, it is not necessary to listen to
the audio identification.
d. Voice identification has been added to numerous VORs. The transmission
consists of a voice announcement, “AIRVILLE VOR” alternating with the usual
Morse Code identification.
effectiveness of the VOR depends upon proper use and adjustment of both ground
and airborne equipment.
1. Accuracy. The
accuracy of course alignment of the VOR is excellent, being generally plus or
minus 1 degree.
2. Roughness. On
some VORs, minor course roughness may be observed, evidenced by course needle or
brief flag alarm activity (some receivers are more susceptible to these
irregularities than others). At a few stations, usually in mountainous terrain,
the pilot may occasionally observe a brief course needle oscillation, similar to
the indication of “approaching station.” Pilots flying over unfamiliar routes
are cautioned to be on the alert for these vagaries, and in particular, to use
the “to/from” indicator to determine positive station passage.
propeller revolutions per minute (RPM) settings or helicopter rotor speeds can
cause the VOR Course Deviation Indicator to fluctuate as much as plus or minus
six degrees. Slight changes to the RPM setting will normally smooth out this
roughness. Pilots are urged to check for this modulation phenomenon prior to
reporting a VOR station or aircraft equipment for unsatisfactory operation.
1-1-4. VOR Receiver Check
a. The FAA VOR
test facility (VOT) transmits a test signal which provides users a convenient
means to determine the operational status and accuracy of a VOR receiver while
on the ground where a VOT is located. The airborne use of VOT is permitted;
however, its use is strictly limited to those areas/altitudes specifically
authorized in the A/FD or appropriate supplement.
b. To use the VOT
service, tune in the VOT frequency on your VOR receiver. With the Course
Deviation Indicator (CDI) centered, the omni-bearing selector should read 0
degrees with the to/from indication showing “from” or the omni-bearing selector
should read 180 degrees with the to/from indication showing “to.” Should the VOR
receiver operate an RMI (Radio Magnetic Indicator), it will indicate 180 degrees
on any omni-bearing selector (OBS) setting. Two means of identification are
used. One is a series of dots and the other is a continuous tone. Information
concerning an individual test signal can be obtained from the local FSS.
c. Periodic VOR
receiver calibration is most important. If a receiver's Automatic Gain Control
or modulation circuit deteriorates, it is possible for it to display acceptable
accuracy and sensitivity close into the VOR or VOT and display out-of-tolerance
readings when located at greater distances where weaker signal areas exist. The
likelihood of this deterioration varies between receivers, and is generally
considered a function of time. The best assurance of having an accurate receiver
is periodic calibration. Yearly intervals are recommended at which time an
authorized repair facility should recalibrate the receiver to the manufacturer's
Aviation Regulations (14 CFR Section 91.171) provides for certain VOR equipment
accuracy checks prior to flight under instrument flight rules. To comply with
this requirement and to ensure satisfactory operation of the airborne system,
the FAA has provided pilots with the following means of checking VOR receiver
1. VOT or a
radiated test signal from an appropriately rated radio repair station.
airborne check points.
3. Certified check
points on the airport surface.
e. A radiated VOT
from an appropriately rated radio repair station serves the same purpose as an
FAA VOR signal and the check is made in much the same manner as a VOT with the
1. The frequency
normally approved by the Federal Communications Commission is 108.0 MHz.
2. Repair stations
are not permitted to radiate the VOR test signal continuously; consequently, the
owner or operator must make arrangements with the repair station to have the
test signal transmitted. This service is not provided by all radio repair
stations. The aircraft owner or operator must determine which repair station in
the local area provides this service. A representative of the repair station
must make an entry into the aircraft logbook or other permanent record
certifying to the radial accuracy and the date of transmission. The owner,
operator or representative of the repair station may accomplish the necessary
checks in the aircraft and make a logbook entry stating the results. It is
necessary to verify which test radial is being transmitted and whether you
should get a “to” or “from” indication.
f. Airborne and ground check points consist of certified radials that should
be received at specific points on the airport surface or over specific landmarks
while airborne in the immediate vicinity of the airport.
1. Should an error
in excess of plus or minus 4 degrees be indicated through use of a ground check,
or plus or minus 6 degrees using the airborne check, Instrument Flight Rules
(IFR) flight must not be attempted without first correcting the source of the
No correction other than the correction card figures supplied by the
manufacturer should be applied in making these VOR receiver checks.
2. Locations of
airborne check points, ground check points and VOTs are published in the A/FD.
3. If a dual
system VOR (units independent of each other except for the antenna) is installed
in the aircraft, one system may be checked against the other. Turn both systems
to the same VOR ground facility and note the indicated bearing to that station.
The maximum permissible variations between the two indicated bearings is 4
1-1-5. Tactical Air
a. For reasons
peculiar to military or naval operations (unusual siting conditions, the
pitching and rolling of a naval vessel, etc.) the civil VOR/Distance Measuring
Equipment (DME) system of air navigation was considered unsuitable for military
or naval use. A new navigational system, TACAN, was therefore developed by the
military and naval forces to more readily lend itself to military and naval
requirements. As a result, the FAA has integrated TACAN facilities with the
civil VOR/DME program. Although the theoretical, or technical principles of
operation of TACAN equipment are quite different from those of VOR/DME
facilities, the end result, as far as the navigating pilot is concerned, is the
same. These integrated facilities are called VORTACs.
b. TACAN ground
equipment consists of either a fixed or mobile transmitting unit. The airborne
unit in conjunction with the ground unit reduces the transmitted signal to a
visual presentation of both azimuth and distance information. TACAN is a pulse
system and operates in the Ultrahigh Frequency (UHF) band of frequencies. Its
use requires TACAN airborne equipment and does not operate through conventional
Omni-directional Range/Tactical Air Navigation (VORTAC)
a. A VORTAC is a
facility consisting of two components, VOR and TACAN, which provides three
individual services: VOR azimuth, TACAN azimuth and TACAN distance (DME) at one
site. Although consisting of more than one component, incorporating more than
one operating frequency, and using more than one antenna system, a VORTAC is
considered to be a unified navigational aid. Both components of a VORTAC are
envisioned as operating simultaneously and providing the three services at all
signals of VOR and TACAN are each identified by three-letter code transmission
and are interlocked so that pilots using VOR azimuth with TACAN distance can be
assured that both signals being received are definitely from the same ground
station. The frequency channels of the VOR and the TACAN at each VORTAC facility
are “paired” in accordance with a national plan to simplify airborne operation.
1-1-7. Distance Measuring Equipment (DME)
a. In the
operation of DME, paired pulses at a specific spacing are sent out from the
aircraft (this is the interrogation) and are received at the ground station. The
ground station (transponder) then transmits paired pulses back to the aircraft
at the same pulse spacing but on a different frequency. The time required for
the round trip of this signal exchange is measured in the airborne DME unit and
is translated into distance (nautical miles) from the aircraft to the ground
b. Operating on the line-of-sight principle, DME furnishes distance
information with a very high degree of accuracy. Reliable signals may be
received at distances up to 199 NM at line-of-sight altitude with an accuracy of
better than 1/2 mile or 3 percent of the distance,
whichever is greater. Distance information received from DME equipment is SLANT
RANGE distance and not actual horizontal distance.
frequency range of a DME according to ICAO Annex 10 is from 960 MHz to 1215 MHz.
Aircraft equipped with TACAN equipment will receive distance information from a
VORTAC automatically, while aircraft equipped with VOR must have a separate DME
equipped with slaved compass systems may be susceptible to heading errors caused
by exposure to magnetic field disturbances (flux fields) found in materials that
are commonly located on the surface or buried under taxiways and ramps. These
materials generate a magnetic flux field that can be sensed by the aircraft's
compass system flux detector or “gate”, which can cause the aircraft's system to
align with the material's magnetic field rather than the earth's natural
magnetic field. The system's erroneous heading may not selfcorrect. Prior to
take off pilots should be aware that a heading misalignment may have occurred
during taxi. Pilots are encouraged to follow the manufacturer's or other
appropriate procedures to correct possible heading misalignment before take off
VORTAC, Instrument Landing System (ILS)/DME, and localizer (LOC)/DME navigation
facilities established by the FAA provide course and distance information from
collocated components under a frequency pairing plan. Aircraft receiving
equipment which provides for automatic DME selection assures reception of
azimuth and distance information from a common source when designated VOR/DME,
VORTAC, ILS/DME, and LOC/DME are selected.
to the limited number of available frequencies, assignment of paired frequencies
is required for certain military noncollocated VOR and TACAN facilities which
serve the same area but which may be separated by distances up to a few miles.
VORTAC, ILS/DME, and LOC/DME facilities are identified by synchronized
identifications which are transmitted on a time share basis. The VOR or
localizer portion of the facility is identified by a coded tone modulated at
1020 Hz or a combination of code and voice. The TACAN or DME is identified by a
coded tone modulated at 1350 Hz. The DME or TACAN coded identification is
transmitted one time for each three or four times that the VOR or localizer
coded identification is transmitted. When either the VOR or the DME is
inoperative, it is important to recognize which identifier is retained for the
operative facility. A single coded identification with a repetition interval of
approximately 30 seconds indicates that the DME is operative.
equipment which provides for automatic DME selection assures reception of
azimuth and distance information from a common source when designated VOR/DME,
VORTAC and ILS/DME navigation facilities are selected. Pilots are cautioned to
disregard any distance displays from automatically selected DME equipment when
VOR or ILS facilities, which do not have the DME feature installed, are being
used for position determination.
1-1-8. Navigational Aid (NAVAID) Service Volumes
a. Most air
navigation radio aids which provide positive course guidance have a designated
standard service volume (SSV). The SSV defines the reception limits of
unrestricted NAVAIDs which are usable for random/unpublished route navigation.
b. A NAVAID will
be classified as restricted if it does not conform to flight inspection signal
strength and course quality standards throughout the published SSV. However, the
NAVAID should not be considered usable at altitudes below that which could be
flown while operating under random route IFR conditions (14 CFR Section 91.177),
even though these altitudes may lie within the designated SSV. Service volume
restrictions are first published in Notices to Airmen (NOTAMs) and then with the
alphabetical listing of the NAVAIDs in the A/FD.
Service Volume limitations do not apply to published IFR routes or procedures.
d. VOR/DME/TACAN Standard Service Volumes (SSV).
service volumes (SSVs) are graphically shown in FIG 1-1-1,
FIG 1-1-2, FIG 1-1-3,
FIG 1-1-4, and FIG 1-1-5. The
SSV of a station is indicated by using the class designator as a prefix to the
station type designation.
TVOR, LDME, and HVORTAC.
Standard High Altitude Service Volume
(See FIG 1-1-5 for altitudes below 1,000 feet).
Standard Low Altitude Service Volume
(See FIG 1-1-5 for altitudes below 1,000 feet).
Standard Terminal Service Volume
(See FIG 1-1-4 for altitudes below 1,000 feet).
2. Within 25 NM, the bottom of the T service volume is defined by the curve
in FIG 1-1-4. Within 40 NM, the bottoms of the L and H
service volumes are defined by the curve in FIG 1-1-5.
Radio Beacon (NDB)
1. NDBs are
classified according to their intended use.
2. The ranges of
NDB service volumes are shown in TBL 1-1-2. The
distances (radius) are the same at all altitudes.
VOR/DME/TACAN Standard Service Volumes
and Range Boundaries
1,000 feet above ground level (AGL) up to and including 12,000 feet AGL at
radial distances out to 25 NM.
L (Low Altitude)
1,000 feet AGL up to and including 18,000 feet AGL at radial distances out to 40
H (High Altitude)
1,000 feet AGL up to and including 14,500 feet AGL at radial distances out to 40
NM. From 14,500 AGL up to and including 60,000 feet at radial distances out to
100 NM. From 18,000 feet AGL up to and including 45,000 feet AGL at radial
distances out to 130 NM.
NDB Service Volumes
*Service ranges of individual facilities may be less than 50 nautical miles
(NM). Restrictions to service volumes are first published as a Notice to Airmen
and then with the alphabetical listing of the NAVAID in the A/FD.
Service Volume Lower Edge Terminal
Service Volume Lower Edge
Standard High and Low
1-1-9. Instrument Landing System (ILS)
1. The ILS is
designed to provide an approach path for exact alignment and descent of an
aircraft on final approach to a runway.
2. The ground
equipment consists of two highly directional transmitting systems and, along the
approach, three (or fewer) marker beacons. The directional transmitters are
known as the localizer and glide slope transmitters.
3. The system may
be divided functionally into three parts:
information: localizer, glide slope;
(b) Range information:
marker beacon, DME; and
information: approach lights, touchdown and centerline lights, runway
radar, or compass locators located at the Outer Marker (OM) or Middle Marker
(MM), may be substituted for marker beacons. DME, when specified in the
procedure, may be substituted for the OM.
5. Where a
complete ILS system is installed on each end of a runway; (i.e., the approach
end of Runway 4 and the approach end of Runway 22) the ILS systems are not in
1. The localizer
transmitter operates on one of 40 ILS channels within the frequency range of
108.10 to 111.95 MHz. Signals provide the pilot with course guidance to the
2. The approach
course of the localizer is called the front course and is used with other
functional parts, e.g., glide slope, marker beacons, etc. The localizer signal
is transmitted at the far end of the runway. It is adjusted for a course width
of (full scale fly-left to a full scale fly-right) of 700 feet at the runway
3. The course line
along the extended centerline of a runway, in the opposite direction to the
front course is called the back course.
Unless the aircraft's ILS equipment includes reverse sensing capability, when
flying inbound on the back course it is necessary to steer the aircraft in the
direction opposite the needle deflection when making corrections from off-course
to on-course. This “flying away from the needle” is also required when flying
outbound on the front course of the localizer. Do not use back course signals
for approach unless a back course approach procedure is published for that
particular runway and the approach is authorized by ATC.
4. Identification is in International Morse Code and consists of a
three-letter identifier preceded by the letter I (DD) transmitted on the
5. The localizer
provides course guidance throughout the descent path to the runway threshold
from a distance of 18 NM from the antenna between an altitude of 1,000 feet
above the highest terrain along the course line and 4,500 feet above the
elevation of the antenna site. Proper off-course indications are provided
throughout the following angular areas of the operational service volume:
(a) To 10 degrees
either side of the course along a radius of 18 NM from the antenna; and
(b) From 10 to 35
degrees either side of the course along a radius of 10 NM. (See
Limits of Localizer Coverage
signals may be received outside these areas.
c. Localizer Type
Directional Aid (LDA)
1. The LDA is of
comparable use and accuracy to a localizer but is not part of a complete ILS.
The LDA course usually provides a more precise approach course than the similar
Simplified Directional Facility (SDF) installation, which may have a course
width of 6 or 12 degrees.
2. The LDA is not
aligned with the runway. Straight-in minimums may be published where alignment
does not exceed 30 degrees between the course and runway. Circling minimums only
are published where this alignment exceeds 30 degrees.
3. A very limited
number of LDA approaches also incorporate a glideslope. These are annotated in
the plan view of the instrument approach chart with a note, “LDA/Glideslope.”
These procedures fall under a newly defined category of approaches called
Approach with Vertical Guidance (APV) described in paragraph
5-4-5, Instrument Approach Procedure Charts, subparagraph
Approach with Vertical Guidance (APV). LDA minima for with and without
glideslope is provided and annotated on the minima lines of the approach chart
as S-LDA/GS and S-LDA. Because the final approach course is not aligned with the
runway centerline, additional maneuvering will be required compared to an ILS
d. Glide Slope/Glide
1. The UHF glide
slope transmitter, operating on one of the 40 ILS channels within the frequency
range 329.15 MHz, to 335.00 MHz radiates its signals in the direction of the
localizer front course. The term “glide path” means that portion of the glide
slope that intersects the localizer.
False glide slope signals may exist in the area of the localizer back course
approach which can cause the glide slope flag alarm to disappear and present
unreliable glide slope information. Disregard all glide slope signal indications
when making a localizer back course approach unless a glide slope is specified
on the approach and landing chart.
2. The glide slope
transmitter is located between 750 feet and 1,250 feet from the approach end of
the runway (down the runway) and offset 250 to 650 feet from the runway
centerline. It transmits a glide path beam 1.4 degrees wide (vertically). The
signal provides descent information for navigation down to the lowest authorized
decision height (DH) specified in the approved ILS approach procedure. The
glidepath may not be suitable for navigation below the lowest authorized DH and
any reference to glidepath indications below that height must be supplemented by
visual reference to the runway environment. Glidepaths with no published DH are
usable to runway threshold.
3. The glide path
projection angle is normally adjusted to 3 degrees above horizontal so that it
intersects the MM at about 200 feet and the OM at about 1,400 feet above the
runway elevation. The glide slope is normally usable to the distance of 10 NM.
However, at some locations, the glide slope has been certified for an extended
service volume which exceeds 10 NM.
4. Pilots must be alert when approaching the glidepath interception. False
courses and reverse sensing will occur at angles considerably greater than the
5. Make every
effort to remain on the indicated glide path.
Avoid flying below the glide path to assure obstacle/terrain clearance is
6. The published
glide slope threshold crossing height (TCH) DOES NOT represent the height of the
actual glide path on-course indication above the runway threshold. It is used as
a reference for planning purposes which represents the height above the runway
threshold that an aircraft's glide slope antenna should be, if that aircraft
remains on a trajectory formed by the four-mile-to-middle marker glidepath
7. Pilots must be
aware of the vertical height between the aircraft's glide slope antenna and the
main gear in the landing configuration and, at the DH, plan to adjust the
descent angle accordingly if the published TCH indicates the wheel crossing
height over the runway threshold may not be satisfactory. Tests indicate a
comfortable wheel crossing height is approximately 20 to 30 feet, depending on
the type of aircraft.
The TCH for a runway is established based on several factors including the
largest aircraft category that normally uses the runway, how airport layout
effects the glide slope antenna placement, and terrain. A higher than optimum
TCH, with the same glide path angle, may cause the aircraft to touch down
further from the threshold if the trajectory of the approach is maintained until
the flare. Pilots should consider the effect of a high TCH on the runway
available for stopping the aircraft.
e. Distance Measuring
1. When installed
with the ILS and specified in the approach procedure, DME may be used:
(a) In lieu of the
(b) As a back
course (BC) final approach fix (FAF); and
(c) To establish
other fixes on the localizer course.
2. In some cases,
DME from a separate facility may be used within Terminal Instrument Procedures
(a) To provide ARC
initial approach segments;
(b) As a FAF for
BC approaches; and
(c) As a
substitute for the OM.
f. Marker Beacon
1. ILS marker
beacons have a rated power output of 3 watts or less and an antenna array
designed to produce an elliptical pattern with dimensions, at 1,000 feet above
the antenna, of approximately 2,400 feet in width and 4,200 feet in length.
Airborne marker beacon receivers with a selective sensitivity feature should
always be operated in the “low” sensitivity position for proper reception of ILS
there are two marker beacons associated with an ILS, the OM and MM. Locations
with a Category II ILS also have an Inner Marker (IM). When an aircraft passes
over a marker, the pilot will receive the indications shown in
(a) The OM
normally indicates a position at which an aircraft at the appropriate altitude
on the localizer course will intercept the ILS glide path.
(b) The MM
indicates a position approximately 3,500 feet from the landing threshold. This
is also the position where an aircraft on the glide path will be at an altitude
of approximately 200 feet above the elevation of the touchdown zone.
(c) The IM will
indicate a point at which an aircraft is at a designated decision height (DH) on
the glide path between the MM and landing threshold.
Marker Passage Indications
D ×− D −
D D D D
D D D D
3. A back course marker normally indicates the ILS back course final
approach fix where approach descent is commenced.
1. Compass locator
transmitters are often situated at the MM and OM sites. The transmitters have a
power of less than 25 watts, a range of at least 15 miles and operate between
190 and 535 kHz. At some locations, higher powered radio beacons, up to 400
watts, are used as OM compass locators. These generally carry Transcribed
Weather Broadcast (TWEB) information.
locators transmit two letter identification groups. The outer locator transmits
the first two letters of the localizer identification group, and the middle
locator transmits the last two letters of the localizer identification group.
h. ILS Frequency
(See TBL 1-1-4.)
Frequency Pairs Allocated for ILS
i. ILS Minimums
1. The lowest
authorized ILS minimums, with all required ground and airborne systems
components operative, are:
(a) Category I. Decision
Height (DH) 200 feet and Runway Visual Range (RVR) 2,400 feet (with touchdown
zone and centerline lighting, RVR 1,800 feet), or (with Autopilot or FD or HUD,
RVR 1,800 feet);
Authorization Category I. DH 150 feet and Runway Visual Range (RVR) 1,400
feet, HUD to DH;
(c) Category II. DH
100 feet and RVR 1,200 feet (with autoland or HUD to touchdown and noted on
authorization, RVR 1,000 feet);
Authorization Category II with Reduced Lighting. DH 100 feet and RVR 1,200
feet with autoland or HUD to touchdown and noted on authorization (touchdown
zone, centerline lighting, and ALSF-2 are not required);
(e) Category IIIa. No
DH or DH below 100 feet and RVR not less than 700 feet;
(f) Category IIIb. No
DH or DH below 50 feet and RVR less than 700 feet but not less than 150 feet;
(g) Category IIIc. No
DH and no RVR limitation.
Special authorization and equipment required for Categories II and III.
j. Inoperative ILS Components
localizer. When the localizer fails, an ILS approach is not authorized.
2. Inoperative glide
slope. When the glide slope fails, the ILS reverts to a nonprecision
See the inoperative component table in the U.S. Government Terminal Procedures
Publication (TPP), for adjustments to minimums due to inoperative airborne or
ground system equipment.
k. ILS Course
1. All pilots
should be aware that disturbances to ILS localizer and glide slope courses may
occur when surface vehicles or aircraft are operated near the localizer or glide
slope antennas. Most ILS installations are subject to signal interference by
either surface vehicles, aircraft or both. ILS CRITICAL AREAS are established
near each localizer and glide slope antenna.
2. ATC issues
control instructions to avoid interfering operations within ILS critical areas
at controlled airports during the hours the Airport Traffic Control Tower (ATCT)
is in operation as follows:
Conditions. Less than ceiling 800 feet and/or visibility 2 miles.
(1) Localizer Critical
Area. Except for aircraft that land, exit a runway,
depart, or execute a missed approach, vehicles and aircraft are not authorized
in or over the critical area when an arriving aircraft is inside the outer
marker (OM) or the fix used in lieu of the OM. Additionally, when conditions are
less than reported ceiling 200 feet or RVR less than 2,000 feet, do not
authorize vehicles or aircraft operations in or over the area when an arriving
aircraft is inside the MM, or in the absence of a MM, ½ mile final.
(2) Glide Slope
Critical Area. Do not authorize vehicles or aircraft
operations in or over the area when an arriving aircraft is inside the ILS outer
marker (OM), or the fix used in lieu of the OM, unless the arriving aircraft has
reported the runway in sight and is circling or side-stepping to land on another
Conditions. At or above ceiling 800 feet and/or visibility 2 miles.
(1) No critical
area protective action is provided under these conditions.
flight crew, under these conditions, should advise the tower that it will
conduct an AUTOLAND or COUPLED approach.
Denver Tower, United 1153, Request Autoland/Coupled
ATC replies with:
United 1153, Denver Tower, Roger, Critical Areas not protected.
holding below 5,000 feet between the outer marker and the airport may cause
localizer signal variations for aircraft conducting the ILS approach.
Accordingly, such holding is not authorized when weather or visibility
conditions are less than ceiling 800 feet and/or visibility 2 miles.
4. Pilots are
cautioned that vehicular traffic not subject to ATC may cause momentary
deviation to ILS course or glide slope signals. Also, critical areas are not
protected at uncontrolled airports or at airports with an operating control
tower when weather or visibility conditions are above those requiring protective
measures. Aircraft conducting coupled or autoland operations should be
especially alert in monitoring automatic flight control systems.
(See FIG 1-1-7.)
Unless otherwise coordinated through Flight
Standards, ILS signals to Category I runways are not flight inspected below the
point that is 100 feet less than the decision altitude (DA). Guidance signal
anomalies may be encountered below this altitude.
Directional Facility (SDF)
a. The SDF
provides a final approach course similar to that of the ILS localizer. It does
not provide glide slope information. A clear understanding of the ILS localizer
and the additional factors listed below completely describe the operational
characteristics and use of the SDF.
b. The SDF
transmits signals within the range of 108.10 to 111.95 MHz.
c. The approach
techniques and procedures used in an SDF instrument approach are essentially the
same as those employed in executing a standard localizer approach except the SDF
course may not be aligned with the runway and the course may be wider, resulting
in less precision.
off-course indications are limited to 35 degrees either side of the course
centerline. Instrument indications received beyond 35 degrees should be
e. The SDF antenna may be offset from the runway centerline. Because of
this, the angle of convergence between the final approach course and the runway
bearing should be determined by reference to the instrument approach procedure
chart. This angle is generally not more than 3 degrees. However, it should be
noted that inasmuch as the approach course originates at the antenna site, an
approach which is continued beyond the runway threshold will lead the aircraft
to the SDF offset position rather than along the runway centerline.
FAA Instrument Landing Systems
f. The SDF signal is fixed at either 6 degrees or 12 degrees as necessary to
provide maximum flyability and optimum course quality.
consists of a three-letter identifier transmitted in Morse Code on the SDF
frequency. The appropriate instrument approach chart will indicate the
identifier used at a particular airport.
1-1-11. Microwave Landing
1. The MLS
provides precision navigation guidance for exact alignment and descent of
aircraft on approach to a runway. It provides azimuth, elevation, and distance.
2. Both lateral
and vertical guidance may be displayed on conventional course deviation
indicators or incorporated into multipurpose cockpit displays. Range information
can be displayed by conventional DME indicators and also incorporated into
3. The system may
be divided into five functions:
(a) Approach azimuth;
(b) Back azimuth;
(c) Approach elevation;
(d) Range; and
(e) Data communications.
4. The standard
configuration of MLS ground equipment includes:
(a) An azimuth
station to perform functions
(a) and (e) above. In
addition to providing azimuth navigation guidance, the station transmits basic
data which consists of information associated directly with the operation of the
landing system, as well as advisory data on the performance of the ground
(b) An elevation
station to perform function (c).
Measuring Equipment (DME) to perform range guidance, both standard DME (DME/N)
and precision DME (DME/P).
5. MLS Expansion
Capabilities. The standard configuration can be expanded by adding one or
more of the following functions or characteristics.
(a) Back azimuth. Provides
lateral guidance for missed approach and departure navigation.
(b) Auxiliary data
transmissions. Provides additional data, including refined airborne
positioning, meteorological information, runway status, and other supplementary
Service Volume (ESV) proportional guidance to 60 degrees.
identification is a four-letter designation starting with the letter M. It is
transmitted in International Morse Code at least six times per minute by the
approach azimuth (and back azimuth) ground equipment.
b. Approach Azimuth
1. The azimuth
station transmits MLS angle and data on one of 200 channels within the frequency
range of 5031 to 5091 MHz.
2. The equipment
is normally located about 1,000 feet beyond the stop end of the runway, but
there is considerable flexibility in selecting sites. For example, for heliport
operations the azimuth transmitter can be collocated with the elevation
3. The azimuth
(See FIG 1-1-8.)
(a) Laterally, at
least 40 degrees on either side of the runway centerline in a standard
(b) In elevation,
up to an angle of 15 degrees and to at least 20,000 feet, and
(c) In range, to
at least 20 NM.
c. Elevation Guidance
1. The elevation
station transmits signals on the same frequency as the azimuth station. A single
frequency is time-shared between angle and data functions.
2. The elevation
transmitter is normally located about 400 feet from the side of the runway
between runway threshold and the touchdown zone.
coverage is provided in the same airspace as the azimuth guidance signals:
(a) In elevation,
to at least +15 degrees;
(b) Laterally, to
fill the Azimuth lateral coverage; and
(c) In range, to
at least 20 NM.
(See FIG 1-1-9.)
d. Range Guidance
1. The MLS
Precision Distance Measuring Equipment (DME/P) functions the same as the
navigation DME described in paragraph 1-1-7, Distance
Measuring Equipment (DME), but there are some technical differences. The beacon
transponder operates in the frequency band 962 to 1105 MHz and responds to an
aircraft interrogator. The MLS DME/P accuracy is improved to be consistent with
the accuracy provided by the MLS azimuth and elevation stations.
2. A DME/P channel
is paired with the azimuth and elevation channel. A complete listing of the
200 paired channels of the DME/P with the angle functions is contained in FAA
Standard 022 (MLS Interoperability and Performance Requirements).
3. The DME/N or
DME/P is an integral part of the MLS and is installed at all MLS facilities
unless a waiver is obtained. This occurs infrequently and only at outlying, low
density airports where marker beacons or compass locators are already in place.
e. Data Communications
1. The data
transmission can include both the basic and auxiliary data words. All MLS
facilities transmit basic data. Where needed, auxiliary data can be transmitted.
2. Coverage limits. MLS
data are transmitted throughout the azimuth (and back azimuth when provided)
3. Basic data
content. Representative data include:
(b) Exact locations of azimuth, elevation and DME/P stations (for MLS
receiver processing functions);
equipment performance level; and
(d) DME/P channel
4. Auxiliary data
content: Representative data include:
(a) 3-D locations
of MLS equipment;
(d) Weather (e.g.,
RVR, ceiling, altimeter setting, wind, wake vortex, wind shear).
1. The MLS has the
capability to fulfill a variety of needs in the approach, landing, missed
approach and departure phases of flight. For example:
(a) Curved and
glide path angles;
(c) Accurate 3-D
positioning of the aircraft in space; and
establishment of boundaries to ensure clearance from obstructions in the
2. While many of
these capabilities are available to any MLS-equipped aircraft, the more
sophisticated capabilities (such as curved and segmented approaches) are
dependent upon the particular capabilities of the airborne equipment.
1. Accuracy. The
MLS provides precision three-dimensional navigation guidance accurate enough for
all approach and landing maneuvers.
2. Coverage. Accuracy
is consistent throughout the coverage volumes. (See
3. Environment. The
system has low susceptibility to interference from weather conditions and
airport ground traffic.
4. Channels. MLS
has 200 channels- enough for any foreseeable need.
5. Data. The MLS
transmits ground-air data messages associated with the systems operation.
6. Range information. Continuous
range information is provided with an accuracy of about 100 feet.
1-1-12. NAVAID Identifier
Removal During Maintenance
During periods of routine
or emergency maintenance, coded identification (or code and voice, where
applicable) is removed from certain FAA NAVAIDs. Removal of identification
serves as a warning to pilots that the facility is officially off the air for
tune-up or repair and may be unreliable even though intermittent or constant
signals are received.
During periods of maintenance VHF ranges may radiate a T-E-S-T code (- D DDD -).
DO NOT attempt to fly a procedure that is NOTAMed out of service even if the
identification is present. In certain cases, the identification may be
transmitted for short periods as part of the testing.
1-1-13. NAVAIDs with
a. Voice equipped
en route radio navigational aids are under the operational control of either a
Flight Service Station (FSS) or an approach control facility. The voice
communication is available on some facilities. Hazardous Inflight Weather
Advisory Service (HIWAS) broadcast capability is available on selected VOR sites
throughout the conterminous U.S. and does not provide two‐way voice
communication. The availability of two‐way voice communication and HIWAS is
indicated in the A/FD and aeronautical charts.
otherwise noted on the chart, all radio navigation aids operate continuously
except during shutdowns for maintenance. Hours of operation of facilities not
operating continuously are annotated on charts and in the A/FD.
1-1-14. User Reports Requested on
NAVAID or Global Navigation Satellite System (GNSS) Performance or Interference
of the National Airspace System (NAS) can render valuable assistance in the
early correction of NAVAID malfunctions or GNSS problems and are encouraged to
report their observations of undesirable performance. Although NAVAIDs are
monitored by electronic detectors, adverse effects of electronic interference,
new obstructions or changes in terrain near the NAVAID can exist without
detection by the ground monitors. Some of the characteristics of malfunction or
deteriorating performance which should be reported are: erratic course or
bearing indications; intermittent, or full, flag alarm; garbled, missing or
obviously improper coded identification; poor quality communications reception;
or, in the case of frequency interference, an audible hum or tone accompanying
radio communications or NAVAID identification. GNSS problems are often
characterized by navigation degradation or service loss indications.
should identify the NAVAID (for example, VOR) malfunction or GNSS problem,
location of the aircraft (i.e., latitude, longitude or bearing/distance from a
NAVAID), magnetic heading, altitude, date and time of the observation, type of
aircraft (make/model/call sign), and description of the condition observed, and
the type of receivers in use (i.e., make/model/software revision). For GNSS
problems, if possible, please note the number of satellites being tracked at the
time of the anomaly. Reports can be made in any of the following ways:
by radio communication to the controlling Air Route Traffic Control Center
(ARTCC), Control Tower, or FSS.
telephone to the nearest FAA facility.
GNSS problems, by internet via the GPS Anomaly Reporting Form at
aircraft that have more than one receiver, there are many combinations of
possible interference between units. This can cause either erroneous navigation
indications or, complete or partial blanking out of the communications. Pilots
should be familiar enough with the radio installation of the particular
airplanes they fly to recognize this type of interference.
In accordance with the 2010 DHS Appropriations Act, the U.S. Coast Guard (USCG)
terminated the transmission of all U.S. LORAN-C signals on 08 Feb 2010. The USCG
also terminated the transmission of the Russian American signals on 01 Aug 2010,
and the Canadian LORAN-C signals on 03 Aug 2010. For more information, visit
http://www.navcen.uscg.gov. Operators should also note that TSO-C60b,
AIRBORNE AREA NAVIGATION EQUIPMENT USING LORAN-C INPUTS, has been canceled by
Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading
Reference System (AHRS)
a. IRUs are
self-contained systems comprised of gyros and accelerometers that provide
aircraft attitude (pitch, roll, and heading), position, and velocity information
in response to signals resulting from inertial effects on system components.
Once aligned with a known position, IRUs continuously calculate position and
velocity. IRU position accuracy decays with time. This degradation is known as
b. INSs combine
the components of an IRU with an internal navigation computer. By programming a
series of waypoints, these systems will navigate along a predetermined track.
c. AHRSs are
electronic devices that provide attitude information to aircraft systems such as
weather radar and autopilot, but do not directly compute position information.
1-1-17. Doppler Radar
Doppler Radar is a
semiautomatic self-contained dead reckoning navigation system (radar sensor plus
computer) which is not continuously dependent on information derived from ground
based or external aids. The system employs radar signals to detect and measure
ground speed and drift angle, using the aircraft compass system as its
directional reference. Doppler is less accurate than INS, however, and the use
of an external reference is required for periodic updates if acceptable position
accuracy is to be achieved on long range flights.
1-1-18. Global Positioning System (GPS)
a. System Overview
The Global Positioning System is a
spacebased radio navigation system used to determine precise position anywhere
in the world. The 24 satellite constellation is designed to ensure at least five
satellites are always visible to a user worldwide. A minimum of four satellites
is necessary for receivers to establish an accurate three-dimensional position.
The receiver uses data from satellites above the mask angle (the lowest
angle above the horizon at which a receiver can use a satellite). The Department
of Defense (DOD) is responsible for operating the GPS satellite constellation
and monitors the GPS satellites to ensure proper operation. Each satellite's
orbital parameters (ephemeris data) are sent to each satellite for broadcast as
part of the data message embedded in the GPS signal. The GPS coordinate system
is the Cartesian earth-centered, earth-fixed coordinates as specified in the
World Geodetic System 1984 (WGS-84).
2. System Availability and
(a) The status of GPS satellites is
broadcast as part of the data message transmitted by the GPS satellites. GPS
status information is also available by means of the U.S. Coast Guard navigation
information service: (703) 313-5907, Internet: http://www.navcen.uscg.gov/.
Additionally, satellite status is available through the Notice to Airmen (NOTAM)
(b) GNSS operational status depends on
the type of equipment being used. For GPS-only equipment TSO-C129 or TSOC196(),
the operational status of non-precision approach capability for flight planning
purposes is provided through a prediction program that is embedded in the
receiver or provided separately.
3. Receiver Autonomous Integrity
Monitoring (RAIM). RAIM is the capability of a GPS receiver to perform integrity
monitoring on itself by ensuring available satellite signals meet the integrity
requirements for a given phase of flight. Without RAIM, the pilot has no
assurance of the GPS position integrity. RAIM provides immediate feedback to the
pilot. This fault detection is critical for performancebased navigation
(PBN) (see Paragraph
1-2-1, Performance-Based Navigation (PBN) and Area Navigation (RNAV), for an
introduction to PBN), because delays of up to two hours can occur before an
erroneous satellite transmission is detected and corrected by the satellite
(a) In order for RAIM to determine if
a satellite is providing corrupted information, at least one satellite, in
addition to those required for navigation, must be in view for the receiver to
perform the RAIM function. RAIM requires a minimum of 5 satellites, or 4
satellites and barometric altimeter input (baro-aiding), to detect an integrity
anomaly. Baro-aiding is a method of augmenting the GPS integrity solution by
using a nonsatellite input source in lieu of the fifth satellite. Some GPS
receivers also have a RAIM capability, called fault detection and exclusion
(FDE), that excludes a failed satellite from the position solution; GPS
receivers capable of FDE require 6 satellites or 5 satellites with baro-aiding.
This allows the GPS receiver to isolate the corrupt satellite signal, remove it
from the position solution, and still provide an integrityassured position. To
ensure that baro-aiding is available, enter the current altimeter setting into
the receiver as described in the operating manual. Do not use the GPS derived
altitude due to the large GPS vertical errors that will make the integrity
monitoring function invalid.
(b) There are
generally two types of RAIM fault messages. The first type of message indicates
that there are not enough satellites available to provide RAIM integrity
monitoring. The GPS navigation solution may be acceptable, but the integrity of
the solution cannot be determined. The second type indicates that the RAIM
integrity monitor has detected a potential error and that there is an
inconsistency in the navigation solution for the given phase of flight. Without
RAIM capability, the pilot has no assurance of the accuracy of the GPS position.
4. Selective Availability. Selective
Availability (SA) is a method by which the accuracy of GPS is intentionally
degraded. This feature was designed to deny hostile use of precise GPS
positioning data. SA was discontinued on May 1, 2000, but many GPS receivers are
designed to assume that SA is still active. New receivers may take advantage of
the discontinuance of SA based on the performance values in ICAO Annex 10.
b. Operational Use of GPS.
operators may use approved GPS equipment in oceanic airspace, certain remote
areas, the National Airspace System and other States as authorized (please
consult the applicable Aeronautical Information Publication). Equipage other
than GPS may be required for the desired operation. GPS navigation is used for
both Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) operations.
1. VFR Operations
(a) GPS navigation has become an asset
to VFR pilots by providing increased navigational capabilities and enhanced
situational awareness. Although GPS has provided many benefits to the VFR pilot,
care must be exercised to ensure that system capabilities are not exceeded. VFR
pilots should integrate GPS navigation with electronic navigation (when
possible), as well as pilotage and dead reckoning.
(b) GPS receivers used for VFR
navigation vary from fully integrated IFR/VFR installation used to support VFR
operations to hand-held devices. Pilots must understand the limitations of the
receivers prior to using in flight to avoid misusing navigation information.
(See TBL 1-1-6.) Most receivers are not intuitive. The
pilot must learn the various keystrokes, knob functions, and displays that are
used in the operation of the receiver. Some manufacturers provide computer-based
tutorials or simulations of their receivers that pilots can use to become
familiar with operating the equipment.
(c) When using GPS for VFR operations,
RAIM capability, database currency, and antenna location are critical areas of
(1) RAIM Capability. VFR GPS panel
mount receivers and hand-held units have no RAIM alerting capability. This
prevents the pilot from being alerted to the loss of the required number of
satellites in view, or the detection of a position error. Pilots should use a
systematic cross-check with other navigation techniques to verify position. Be
suspicious of the GPS position if a disagreement exists between the two
(2) Database Currency. Check the
currency of the database. Databases must be updated for IFR operations and
should be updated for all other operations. However, there is no requirement for
databases to be updated for VFR navigation. It is not recommended to use a
moving map with an outdated database in and around critical airspace. Pilots
using an outdated database should verify waypoints using current aeronautical
products; for example, Airport/Facility Directory, Sectional Chart, or En Route
(3) Antenna Location. The antenna
location for GPS receivers used for IFR and VFR operations may differ. VFR
antennae are typically placed for convenience more than performance, while IFR
installations ensure a clear view is provided with the satellites. Antennae not
providing a clear view have a greater opportunity to lose the satellite
navigational signal. This is especially true in the case of hand-held GPS
receivers. Typically, suction cups are used to place the GPS antennas on the
inside of cockpit windows. While this method has great utility, the antenna
location is limited to the cockpit or cabin which rarely provides a clear view
of all available satellites. Consequently, signal losses may occur due to
aircraft structure blocking satellite signals, causing a loss of navigation
capability. These losses, coupled with a lack of RAIM capability, could present
erroneous position and navigation information with no warning to the pilot.
While the use of a hand-held GPS for VFR operations is not limited by
regulation, modification of the aircraft, such as installing a panel- or
yoke-mounted holder, is governed by 14 CFR Part 43. Consult with your mechanic
to ensure compliance with the regulation and safe installation.
(d) Do not solely
rely on GPS for VFR navigation. No design standard of accuracy or integrity is
used for a VFR GPS receiver. VFR GPS receivers should be used in conjunction
with other forms of navigation during VFR operations to ensure a correct route
of flight is maintained. Minimize head-down time in the aircraft by being
familiar with your GPS receiver's operation and by keeping eyes outside scanning
for traffic, terrain, and obstacles.
(e) VFR Waypoints
(1) VFR waypoints provide VFR pilots
with a supplementary tool to assist with position awareness while navigating
visually in aircraft equipped with area navigation receivers. VFR waypoints
should be used as a tool to supplement current navigation procedures. The uses
of VFR waypoints include providing navigational aids for pilots unfamiliar with
an area, waypoint definition of existing reporting points, enhanced navigation
in and around Class B and Class C airspace, and enhanced navigation around
Special Use Airspace. VFR pilots should rely on appropriate and current
aeronautical charts published specifically for visual navigation. If operating
in a terminal area, pilots should take advantage of the Terminal Area Chart
available for that area, if published. The use of VFR waypoints does not relieve
the pilot of any responsibility to comply with the operational requirements of
14 CFR Part 91.
(2) VFR waypoint names (for
computer-entry and flight plans) consist of five letters beginning with the
letters “VP” and are retrievable from navigation databases. The VFR waypoint
names are not intended to be pronounceable, and they are not for use in ATC
communications. On VFR charts, stand-alone VFR waypoints will be portrayed using
the same four-point star symbol used for IFR waypoints. VFR waypoints collocated
with visual check points on the chart will be identified by small magenta flag
symbols. VFR waypoints collocated with visual check points will be pronounceable
based on the name of the visual check point and may be used for ATC
communications. Each VFR waypoint name will appear in parentheses adjacent to
the geographic location on the chart. Latitude/longitude data for all
established VFR waypoints may be found in the appropriate regional
Airport/Facility Directory (A/FD).
(3) VFR waypoints may not be used on
IFR flight plans. VFR waypoints are not recognized by the IFR system and will be
rejected for IFR routing purposes.
(4) Pilots may use the five-letter
identifier as a waypoint in the route of flight section on a VFR flight plan.
Pilots may use the VFR waypoints only when operating under VFR conditions. The
point may represent an intended course change or describe the planned route of
flight. This VFR filing would be similar to how a VOR would be used in a route
(5) VFR waypoints intended for use
during flight should be loaded into the receiver while on the ground. Once
airborne, pilots should avoid programming routes or VFR waypoint chains into
(6) Pilots should be vigilant to see
and avoid other traffic when near VFR waypoints. With the increased use of GPS
navigation and accuracy, expect increased traffic near VFR waypoints. Regardless
of the class of airspace, monitor the available ATC frequency for traffic
information on other aircraft operating in the vicinity. See Paragraph
7-5-2, VFR in
Congested Areas, for more information.
2. IFR Use of GPS
(a) General Requirements.
Authorization to conduct any GPS operation under IFR requires:
(1) GPS navigation equipment used for
IFR operations must be approved in accordance with the requirements specified in
Technical Standard Order (TSO) TSO-C129(), TSO-C196(), TSO-C145(), or
TSO-C146(), and the installation must be done in accordance with Advisory
Circular AC 20-138(), Airworthiness Approval of Positioning and Navigation
Systems. Equipment approved in accordance with TSO-C115a does not meet the
requirements of TSO-C129. Visual flight rules (VFR) and hand-held GPS systems
are not authorized for IFR navigation, instrument approaches, or as a principal
instrument flight reference.
using unaugmented GPS (TSOC129() or TSOC196()) for navigation under IFR must
be equipped with an alternate approved and operational means of navigation
suitable for navigating the proposed route of flight. (Examples of alternate
navigation equipment include VOR or DME/DME/IRU capability). Active monitoring
of alternative navigation equipment is not required when RAIM is available for
integrity monitoring. Active monitoring of an alternate means of navigation is
required when the GPS RAIM capability is lost.
(3) Procedures must be established for
use in the event that the loss of RAIM capability is predicted to occur. In
situations where RAIM is predicted to be unavailable, the flight must rely on
other approved navigation equipment, reroute to where RAIM is available, delay
departure, or cancel the flight.
(4) The GPS operation must be
conducted in accordance with the FAA-approved aircraft flight manual (AFM) or
flight manual supplement. Flight crew members must be thoroughly familiar with
the particular GPS equipment installed in the aircraft, the receiver operation
manual, and the AFM or flight manual supplement. Operation, receiver
presentation and capabilities of GPS equipment vary. Due to these differences,
operation of GPS receivers of different brands, or even models of the same
brand, under IFR should not be attempted without thorough operational knowledge.
Most receivers have a built-in simulator mode, which allows the pilot to become
familiar with operation prior to attempting operation in the aircraft.
(5) Aircraft navigating by
IFR-approved GPS are considered to be performance-based navigation (PBN)
aircraft and have special equipment suffixes. File the appropriate equipment
suffix in accordance with
TBL 5-1-3 on the
ATC flight plan. If GPS avionics become inoperative, the pilot should advise ATC
and amend the equipment suffix.
(6) Prior to any GPS IFR operation,
the pilot must review appropriate NOTAMs and aeronautical information. (See GPS
(b) Database Requirements.
navigation data must be current and appropriate for the region of intended
operation and should include the navigation aids, waypoints, and relevant coded
terminal airspace procedures for the departure, arrival, and alternate
(1) Further database guidance for
terminal and en route requirements may be found in AC 90100(),
and En Route Area Navigation (RNAV) Operations.
(2) Further database guidance on
Required Navigation Performance (RNP) instrument approach operations, RNP
terminal, and RNP en route requirements may be found in AC 90105(),
Guidance for RNP Operations and Barometric Vertical Navigation in the U.S.
National Airspace System.
(3) All approach procedures to be
flown must be retrievable from the current airborne navigation database supplied
by the equipment manufacturer or other FAA-approved source. The system must be
able to retrieve the procedure by name from the aircraft navigation database,
not just as a manually entered series of waypoints. Manual entry of waypoints
using latitude/longitude or place/bearing is not permitted for approach
(4) Prior to using a procedure or
waypoint retrieved from the airborne navigation database, the pilot should
verify the validity of the database. This verification should include the
following preflight and inflight steps:
Determine the date of database
issuance, and verify that the date/time of proposed use is before the expiration
Verify that the database provider
has not published a notice limiting the use of the specific waypoint or
Determine that the waypoints and
transition names coincide with names found on the procedure chart. Do not use
waypoints which do not exactly match the spelling shown on published procedure
Determine that the waypoints are
logical in location, in the correct order, and their orientation to each other
is as found on the procedure chart, both laterally and vertically.
There is no specific requirement to check each waypoint latitude and longitude,
type of waypoint and/or altitude constraint, only the general relationship of
waypoints in the procedure, or the logic of an individual waypoint's location.
cursory check of procedure logic or individual waypoint location, specified in
[b] above, indicates a potential error, do not use the retrieved procedure or
waypoint until a verification of latitude and longitude, waypoint type, and
altitude constraints indicate full conformity with the published data.
(5) Air carrier and commercial
operators must meet the appropriate provisions of their approved operations
[a] During domestic operations for
commerce or for hire, operators must have a second navigation system capable of
reversion or contingency operations.
[b] Operators must have two
independent navigation systems appropriate to the route to be flown, or one
system that is suitable and a second, independent backup capability that allows
the operator to proceed safely and land at a different airport, and the aircraft
must have sufficient fuel (reference 14 CFR 121.349, 125.203, 129.17, and
135.165). These rules ensure the safety of the operation by preventing a single
point of failure.
An aircraft approved for multisensor navigation and equipped with a single
navigation system must maintain an ability to navigate or proceed safely in the
event that any one component of the navigation system fails, including the
flight management system (FMS). Retaining a FMSindependent VOR capability would
satisfy this requirement.
[c] The requirements for a second
system apply to the entire set of equipment needed to achieve the navigation
capability, not just the individual components of the system such as the radio
navigation receiver. For example, to use two RNAV systems (e.g., GPS and
DME/DME/IRU) to comply with the requirements, the aircraft must be equipped with
two independent radio navigation receivers and two independent navigation
computers (e.g., flight management systems (FMS)). Alternatively, to comply with
the requirements using a single RNAV system with an installed and operable VOR
capability, the VOR capability must be independent of the FMS.
[d] To satisfy the requirement for two
independent navigation systems, if the primary navigation system is GPS-based,
the second system must be independent of GPS (for example, VOR or DME/DME/IRU).
This allows continued navigation in case of failure of the GPS or WAAS services.
Recognizing that GPS interference and test events resulting in the loss of GPS
services have become more common, the FAA requires operators conducting IFR
operations under 14 CFR 121.349, 125.203, 129.17 and 135.65 to retain a nonGPS
navigation capability consisting of either DME/DME, IRU, or VOR for en route and
terminal operations, and VOR and ILS for final approach. Since this system is to
be used as a reversionary capability, single equipage is sufficient.
3. Oceanic, Domestic, En Route, and
Terminal Area Operations
(a) Conduct GPS IFR operations in
oceanic areas only when approved avionics systems are installed. TSO-C196()
users and TSO-C129() GPS users authorized for Class A1, A2, B1, B2, C1, or C2
operations may use GPS in place of another approved means of long-range
navigation, such as dual INS. (See TBL 1-1-5 and
TBL 1-1-6.) Aircraft with a single installation GPS,
meeting the above specifications, are authorized to operate on short oceanic
routes requiring one means of long-range navigation (reference AC 20138(),
(b) Conduct GPS domestic, en route,
and terminal IFR operations only when approved avionics systems are installed.
Pilots may use GPS via TSO-C129() authorized for Class A1, B1, B3, C1, or C3
operations GPS via TSOC196(); or GPS/WAAS with either TSOC145() or TSOC146().
When using TSOC129() or TSOC196() receivers, the avionics necessary to receive
all of the ground-based facilities appropriate for the route to the destination
airport and any required alternate airport must be installed and operational.
Ground-based facilities necessary for these routes must be operational.
(1) GPS en route IFR operations may be
conducted in Alaska outside the operational service volume of ground-based
navigation aids when a TSO-C145() or TSO-C146() GPS/wide area augmentation
system (WAAS) system is installed and operating. WAAS is the U.S. version of a
satellitebased augmentation system (SBAS).
[a] In Alaska,
aircraft may operate on GNSS Qroutes with GPS (TSOC129 () or TSOC196 ())
equipment while the aircraft remains in Air Traffic Control (ATC) radar
surveillance or with GPS/WAAS (TSOC145 () or TSOC146 ()) which does not
require ATC radar surveillance.
[b] In Alaska, aircraft may only
operate on GNSS Troutes with GPS/WAAS (TSOC145 () or TSOC146 ()) equipment.
(2) Ground-based navigation equipment
is not required to be installed and operating for en route IFR operations when
using GPS/WAAS navigation systems. All operators should ensure that an alternate
means of navigation is available in the unlikely event the GPS/WAAS navigation
system becomes inoperative.
(3) Q-routes and T-routes outside
Alaska. Qroutes require system performance currently met by GPS, GPS/WAAS, or
DME/DME/IRU RNAV systems that satisfy the criteria discussed in AC 90-100(),
U.S. Terminal and En Route Area Navigation (RNAV) Operations. Troutes
require GPS or GPS/WAAS equipment.
AIM Paragraph 5-3-4,
Airways and Route Systems
(c) GPS IFR approach/departure
operations can be conducted when approved avionics systems are installed and the
following requirements are met:
(1) The aircraft is TSO-C145() or
TSO-C146() or TSO-C196() or TSO-C129() in Class A1, B1, B3, C1, or C3; and
(2) The approach/departure must be
retrievable from the current airborne navigation database in the navigation
computer. The system must be able to retrieve the procedure by name from the
aircraft navigation database. Manual entry of waypoints using latitude/longitude
or place/bearing is not permitted for approach procedures.
(3) The authorization to fly
instrument approaches/departures with GPS is limited to U.S. airspace.
(4) The use of GPS in any other
airspace must be expressly authorized by the FAA Administrator.
(5) GPS instrument approach/departure
operations outside the U.S. must be authorized by the appropriate sovereign
4. Departures and Instrument Departure
The GPS receiver must be set to terminal (±1
NM) CDI sensitivity and the navigation routes contained in the database in order
to fly published IFR charted departures and DPs. Terminal RAIM should be
automatically provided by the receiver. (Terminal RAIM for departure may not be
available unless the waypoints are part of the active flight plan rather than
proceeding direct to the first destination.) Certain segments of a DP may
require some manual intervention by the pilot, especially when radar vectored to
a course or required to intercept a specific course to a waypoint. The database
may not contain all of the transitions or departures from all runways and some
GPS receivers do not contain DPs in the database. It is necessary that
helicopter procedures be flown at 70 knots or less since helicopter departure
procedures and missed approaches use a 20:1 obstacle clearance surface (OCS),
which is double the fixed-wing OCS, and turning areas are based on this speed as
5. GPS Instrument Approach Procedures
(a) GPS overlay approaches are
designated non-precision instrument approach procedures that pilots are
authorized to fly using GPS avionics. Localizer (LOC), localizer type
directional aid (LDA), and simplified directional facility (SDF) procedures are
not authorized. Overlay procedures are identified by the “name of the procedure”
and “or GPS” (e.g., VOR/DME or GPS RWY 15) in the title. Authorized procedures
must be retrievable from a current onboard navigation database. The navigation
database may also enhance position orientation by displaying a map containing
information on conventional NAVAID approaches. This approach information should
not be confused with a GPS overlay approach (see the receiver operating manual,
AFM, or AFM Supplement for details on how to identify these approaches in the
Overlay approaches do not adhere to the design criteria described in Paragraph
5-4-5m, Area Navigation (RNAV) Instrument Approach Charts, for stand-alone GPS
approaches. Overlay approach criteria is based on the design criteria used for
ground-based NAVAID approaches.
(b) Stand-alone approach procedures
specifically designed for GPS systems have replaced many of the original overlay
approaches. All approaches that contain “GPS” in the title (e.g., “VOR or GPS
RWY 24,” “GPS RWY 24,” or “RNAV (GPS) RWY 24”) can be flown using GPS.
GPS-equipped aircraft do not need underlying ground-based NAVAIDs or associated
aircraft avionics to fly the approach. Monitoring the underlying approach with
ground-based NAVAIDs is suggested when able. Existing overlay approaches may be
requested using the GPS title; for example, the VOR or GPS RWY 24 may be
requested as “GPS RWY 24.” Some GPS procedures have a Terminal Arrival Area
(TAA) with an underlining RNAV approach.
(c) For flight
planning purposes, TSOC129() and TSOC196()-equipped users (GPS users) whose
navigation systems have fault detection and exclusion (FDE) capability, who
perform a preflight RAIM prediction for the approach integrity at the airport
where the RNAV (GPS) approach will be flown, and have proper knowledge and any
required training and/or approval to conduct a GPSbased IAP, may file based on
a GPS-based IAP at either the destination or the alternate airport, but not at
both locations. At the alternate airport, pilots may plan for:
(1) Lateral navigation (LNAV) or
circling minimum descent altitude (MDA);
(2) LNAV/vertical navigation
(LNAV/VNAV) DA, if equipped with and using approved barometric vertical
navigation (baroVNAV) equipment;
(3) RNP 0.3 DA on an RNAV (RNP) IAP,
if they are specifically authorized users using approved baroVNAV equipment and
the pilot has verified required navigation performance (RNP) availability
through an approved prediction program.
(d) If the above conditions cannot be
met, any required alternate airport must have an approved instrument approach
procedure other than GPS-based that is anticipated to be operational and
available at the estimated time of arrival, and which the aircraft is equipped
(e) Procedures for Accomplishing GPS
(1) An RNAV (GPS) procedure may be
associated with a Terminal Arrival Area (TAA). The basic design of the RNAV
procedure is the “T” design or a modification of the “T” (See Paragraph
Terminal Arrival Area (TAA), for complete information).
(2) Pilots cleared by ATC for an RNAV
(GPS) approach should fly the full approach from an Initial Approach Waypoint
(IAWP) or feeder fix. Randomly joining an approach at an intermediate fix does
not assure terrain clearance.
(3) When an approach has been loaded
in the navigation system, GPS receivers will give an “arm” annunciation 30 NM
straight line distance from the airport/heliport reference point. Pilots should
arm the approach mode at this time if not already armed (some receivers arm
automatically). Without arming, the receiver will not change from en route CDI
and RAIM sensitivity of ±5 NM either side of centerline to ±1 NM terminal
sensitivity. Where the IAWP is inside this 30 mile point, a CDI sensitivity
change will occur once the approach mode is armed and the aircraft is inside 30
NM. Where the IAWP is beyond 30 NM from the airport/heliport reference point and
the approach is armed, the CDI sensitivity will not change until the aircraft is
within 30 miles of the airport/heliport reference point. Feeder route obstacle
clearance is predicated on the receiver being in terminal (±1 NM) CDI
sensitivity and RAIM within 30 NM of the airport/heliport reference point;
therefore, the receiver should always be armed (if required) not later than the
30 NM annunciation.
(4) The pilot must be aware of what
bank angle/turn rate the particular receiver uses to compute turn anticipation,
and whether wind and airspeed are included in the receiver's calculations. This
information should be in the receiver operating manual. Over or under banking
the turn onto the final approach course may significantly delay getting on
course and may result in high descent rates to achieve the next segment
(5) When within 2 NM of the Final
Approach Waypoint (FAWP) with the approach mode armed, the approach mode will
switch to active, which results in RAIM and CDI changing to approach
sensitivity. Beginning 2 NM prior to the FAWP, the full scale CDI sensitivity
will smoothly change from ±1 NM to ±0.3 NM at the FAWP. As sensitivity changes
from ±1 NM to ±0.3 NM approaching the FAWP, with the CDI not centered, the
corresponding increase in CDI displacement may give the impression that the
aircraft is moving further away from the intended course even though it is on an
acceptable intercept heading. Referencing the digital track displacement
information (cross track error), if it is available in the approach mode, may
help the pilot remain position oriented in this situation. Being established on
the final approach course prior to the beginning of the sensitivity change at 2
NM will help prevent problems in interpreting the CDI display during ramp down.
Therefore, requesting or accepting vectors which will cause the aircraft to
intercept the final approach course within 2 NM of the FAWP is not recommended.
receiving vectors to final, most receiver operating manuals suggest placing the
receiver in the non-sequencing mode on the FAWP and manually setting the course.
This provides an extended final approach course in cases where the aircraft is
vectored onto the final approach course outside of any existing segment which is
aligned with the runway. Assigned altitudes must be maintained until established
on a published segment of the approach. Required altitudes at waypoints outside
the FAWP or stepdown fixes must be considered. Calculating the distance to the
FAWP may be required in order to descend at the proper location.
(7) Overriding an automatically
selected sensitivity during an approach will cancel the approach mode
annunciation. If the approach mode is not armed by 2 NM prior to the FAWP, the
approach mode will not become active at 2 NM prior to the FAWP, and the
equipment will flag. In these conditions, the RAIM and CDI sensitivity will not
ramp down, and the pilot should not descend to MDA, but fly to the MAWP and
execute a missed approach. The approach active annunciator and/or the receiver
should be checked to ensure the approach mode is active prior to the FAWP.
(8) Do not attempt to fly an approach
unless the procedure in the onboard database is current and identified as “GPS”
on the approach chart. The navigation database may contain information about
non-overlay approach procedures that enhances position orientation generally by
providing a map, while flying these approaches using conventional NAVAIDs. This
approach information should not be confused with a GPS overlay approach (see the
receiver operating manual, AFM, or AFM Supplement for details on how to identify
these procedures in the navigation database). Flying point to point on the
approach does not assure compliance with the published approach procedure. The
proper RAIM sensitivity will not be available and the CDI sensitivity will not
automatically change to ±0.3 NM. Manually setting CDI sensitivity does not
automatically change the RAIM sensitivity on some receivers. Some existing
non-precision approach procedures cannot be coded for use with GPS and will not
be available as overlays.
(9) Pilots should pay particular
attention to the exact operation of their GPS receivers for performing holding
patterns and in the case of overlay approaches, operations such as procedure
turns. These procedures may require manual intervention by the pilot to stop the
sequencing of waypoints by the receiver and to resume automatic GPS navigation
sequencing once the maneuver is complete. The same waypoint may appear in the
route of flight more than once consecutively (for example, IAWP, FAWP, MAHWP on
a procedure turn). Care must be exercised to ensure that the receiver is
sequenced to the appropriate waypoint for the segment of the procedure being
flown, especially if one or more fly-overs are skipped (for example, FAWP rather
than IAWP if the procedure turn is not flown). The pilot may have to sequence
past one or more fly-overs of the same waypoint in order to start GPS automatic
sequencing at the proper place in the sequence of waypoints.
(10) Incorrect inputs into the GPS
receiver are especially critical during approaches. In some cases, an incorrect
entry can cause the receiver to leave the approach mode.
(11) A fix on an overlay approach
identified by a DME fix will not be in the waypoint sequence on the GPS receiver
unless there is a published name assigned to it. When a name is assigned, the
along track distance (ATD) to the waypoint may be zero rather than the DME
stated on the approach chart. The pilot should be alert for this on any overlay
procedure where the original approach used DME.
(12) If a visual descent point (VDP)
is published, it will not be included in the sequence of waypoints. Pilots are
expected to use normal piloting techniques for beginning the visual descent,
such as ATD.
stepdown fixes in the final approach segment may or may not be coded in the
waypoint sequence of the aircraft's navigation database and must be identified
using ATD. Stepdown fixes in the final approach segment of RNAV (GPS) approaches
are being named, in addition to being identified by ATD. However, GPS avionics
may or may not accommodate waypoints between the FAF and MAP. Pilots must know
the capabilities of their GPS equipment and continue to identify stepdown fixes
using ATD when necessary.
(f) Missed Approach
(1) A GPS missed approach requires
pilot action to sequence the receiver past the MAWP to the missed approach
portion of the procedure. The pilot must be thoroughly familiar with the
activation procedure for the particular GPS receiver installed in the aircraft
and must initiate appropriate action after the MAWP. Activating the missed
approach prior to the MAWP will cause CDI sensitivity to immediately change to
terminal (±1NM) sensitivity and the receiver will continue to navigate to the
MAWP. The receiver will not sequence past the MAWP. Turns should not begin prior
to the MAWP. If the missed approach is not activated, the GPS receiver will
display an extension of the inbound final approach course and the ATD will
increase from the MAWP until it is manually sequenced after crossing the MAWP.
(2) Missed approach routings in which
the first track is via a course rather than direct to the next waypoint require
additional action by the pilot
to set the course. Being familiar with all
of the inputs required is especially critical during this phase of flight.
(g) GPS NOTAMs/Aeronautical Information
(1) GPS satellite outages are issued
as GPS NOTAMs both domestically and internationally. However, the effect of an
outage on the intended operation cannot be determined unless the pilot has a
RAIM availability prediction program which allows excluding a satellite which is
predicted to be out of service based on the NOTAM information.
(2) The terms UNRELIABLE and MAY NOT
BE AVAILABLE are used in conjunction with GPS NOTAMs. Both UNRELIABLE and MAY
NOT BE AVAILABLE are advisories to pilots indicating the expected level of
service may not be available. UNRELIABLE does not mean there is a problem with
GPS signal integrity. If GPS service is available, pilots may continue
operations. If the LNAV or LNAV/VNAV service is available, pilots may use the
displayed level of service to fly the approach. GPS operation may be NOTAMed
UNRELIABLE or MAY NOT BE AVAILABLE due to testing or anomalies. (Pilots are
encouraged to report GPS anomalies, including degraded operation and/or loss of
service, as soon as possible, reference paragraph
1-1-14.) When GPS testing NOTAMS are published and testing is actually
occurring, Air Traffic Control will advise pilots requesting or cleared for a
GPS or RNAV (GPS) approach that GPS may not be available and request intentions.
If pilots have reported GPS anomalies, Air Traffic Control will request the
pilot's intentions and/or clear the pilot for an alternate approach, if
available and operational.
The following is an example of a GPS testing NOTAM:
!GPS 06/001 ZAB NAV GPS (INCLUDING WAAS, GBAS, AND ADSB) MAY NOT BE
AVAILABLE WITHIN A 468NM RADIUS CENTERED AT 330702N1062540W (TCS 093044)
FL400UNL DECREASING IN AREA WITH A DECREASE IN ALTITUDE DEFINED AS: 425NM
RADIUS AT FL250, 360NM RADIUS AT 10000FT, 354NM RADIUS AT 4000FT AGL, 327NM
RADIUS AT 50FT AGL. 14060703001406071200.
(3) Civilian pilots may obtain GPS
RAIM availability information for non-precision approach procedures by: using a
manufacturersupplied RAIM prediction tool; or using the generic tool at
www.raimprediction.net. The FAA is developing a replacement prediction tool at
www.sapt.faa.gov scheduled for transition in 2014. Pilots can also request GPS
RAIM aeronautical information from a flight service station during preflight
briefings. GPS RAIM aeronautical information can be obtained for a period of 3
hours (for example, if you are scheduled to arrive at 1215 hours, then the GPS
RAIM information is available from 1100 to 1400 hours) or a 24-hour timeframe at
a particular airport. FAA briefers will provide RAIM information for a period of
1 hour before to 1 hour after the ETA hour, unless a specific timeframe is
requested by the pilot. If flying a published GPS departure, a RAIM prediction
should also be requested for the departure airport.
(4) The military provides airfield
specific GPS RAIM NOTAMs for non-precision approach procedures at military
airfields. The RAIM outages are issued as M-series NOTAMs and may be obtained
for up to 24 hours from the time of request.
manufacturers and/or database suppliers may supply “NOTAM” type information
concerning database errors. Pilots should check these sources, when available,
to ensure that they have the most current information concerning their
(h) Receiver Autonomous Integrity
(1) RAIM outages may occur due to an
insufficient number of satellites or due to unsuitable satellite geometry which
causes the error in the position solution to become too large. Loss of satellite
reception and RAIM warnings may occur due to aircraft dynamics (changes in pitch
or bank angle). Antenna location on the aircraft, satellite position relative to
the horizon, and aircraft attitude may affect reception of one or more
satellites. Since the relative positions of the satellites are constantly
changing, prior experience with the airport does not guarantee reception at all
times, and RAIM availability should always be checked.
(2) If RAIM is not available, use
another type of navigation and approach system, select another route or
destination, or delay the trip until RAIM is predicted to be available on
arrival. On longer flights, pilots should consider rechecking the RAIM
prediction for the destination during the flight. This may provide an early
indication that an unscheduled satellite outage has occurred since takeoff.
(3) If a RAIM failure/status
annunciation occurs prior to the final approach waypoint (FAWP), the approach
should not be completed since GPS no longer provides the required integrity. The
receiver performs a RAIM prediction by 2 NM prior to the FAWP to ensure that
RAIM is available as a condition for entering the approach mode. The pilot
should ensure the receiver has sequenced from “Armed” to “Approach” prior to the
FAWP (normally occurs 2 NM prior). Failure to sequence may be an indication of
the detection of a satellite anomaly, failure to arm the receiver (if required),
or other problems which preclude flying the approach.
(4) If the receiver does not sequence
into the approach mode or a RAIM failure/status annunciation occurs prior to the
FAWP, the pilot must not initiate the approach or descend, but instead proceed
to the missed approach waypoint ( MAWP) via the FAWP, perform a missed approach,
and contact ATC as soon as practical. The GPS receiver may continue to operate
after a RAIM flag/status annunciation appears, but the navigation information
should be considered advisory only. Refer to the receiver operating manual for
specific indications and instructions associated with loss of RAIM prior to the
(5) If the RAIM flag/status
annunciation appears after the FAWP, the pilot should initiate a climb and
execute the missed approach. The GPS receiver may continue to operate after a
RAIM flag/status annunciation appears, but the navigation information should be
considered advisory only. Refer to the receiver operating manual for operating
mode information during a RAIM annunciation.
(1) GPS receivers navigate from one
defined point to another retrieved from the aircraft's onboard navigational
database. These points are waypoints (5letter pronounceable name), existing VHF
intersections, DME fixes with 5-letter pronounceable names and 3letter NAVAID
IDs. Each waypoint is a geographical location defined by a latitude/longitude
geographic coordinate. These 5-letter waypoints, VHF intersections, 5-letter
pronounceable DME fixes and 3-letter NAVAID IDs are published on various FAA
aeronautical navigation products (IFR Enroute Charts, VFR Charts, Terminal
Procedures Publications, etc.).
(2) A Computer Navigation Fix (CNF) is
also a point defined by a latitude/longitude coordinate and is required to
support Performance-Based Navigation (PBN) operations. The GPS receiver uses
CNFs in conjunction with waypoints to navigate from point to point. However,
CNFs are not recognized by ATC. ATC does not maintain CNFs in their database and
they do not use CNFs for any air traffic control purpose. CNFs may or may not be
charted on FAA aeronautical navigation products, are listed in the chart
legends, and are for advisory purposes only. Pilots are not to use CNFs for
point to point navigation (proceed direct), filing a flight plan, or in
aircraft/ATC communications. CNFs that do appear on aeronautical charts allow
pilots increased situational awareness by identifying points in the aircraft
database route of flight with points on the aeronautical chart. CNFs are random
fiveletter identifiers, not pronounceable like waypoints and placed in
parenthesis. Eventually, all CNFs will begin with the letters “CF” followed by
three consonants (for example, CFWBG). This fiveletter identifier will be found
next to an “x” on enroute charts and possibly on an approach chart. On
instrument approach procedures (charts) in the terminal procedures publication,
CNFs may represent unnamed DME fixes, beginning and ending points of DME arcs,
and sensor (groundbased signal i.e., VOR, NDB, ILS) final approach fixes on GPS
overlay approaches. These CNFs provide the GPS with points on the procedure that
allow the overlay approach to mirror the groundbased sensor approach. These
points should only be used by the GPS system for navigation and should not be
used by pilots for any other purpose on the approach. The CNF concept has not
been adopted or recognized by the International Civil Aviation Organization
approaches use fly-over and fly-by waypoints to join route segments on an
approach. Fly-by waypoints connect the two segments by allowing the aircraft to
turn prior to the current waypoint in order to roll out on course to the next
waypoint. This is known as turn anticipation and is compensated for in the
airspace and terrain clearances. The MAWP and the missed approach holding
waypoint (MAHWP) are normally the only two waypoints on the approach that are
not fly-by waypoints. Fly-over waypoints are used when the aircraft must overfly
the waypoint prior to starting a turn to the new course. The symbol for a
flyover waypoint is a circled waypoint. Some waypoints may have dual use; for
example, as a fly-by waypoint when used as an IF for a NoPT route and as a
flyover waypoint when the same waypoint is also used as an IAF/IF holdinlieu
of PT. When this occurs, the less restrictive (flyby) symbology will be
charted. Overlay approach charts and some early stand-alone GPS approach charts
may not reflect this convention.
(4) Unnamed waypoints for each airport
will be uniquely identified in the database. Although the identifier may be used
at different airports (for example, RW36 will be the identifier at each airport
with a runway 36), the actual point, at each airport, is defined by a specific
(5) The runway threshold waypoint,
normally the MAWP, may have a five-letter identifier (for example, SNEEZ) or be
coded as RW## (for example, RW36, RW36L). MAWPs located at the runway threshold
are being changed to the RW## identifier, while MAWPs not located at the
threshold will have a five-letter identifier. This may cause the approach chart
to differ from the aircraft database until all changes are complete. The runway
threshold waypoint is also used as the center of the Minimum Safe Altitude (MSA)
on most GPS approaches.
(j) Position Orientation.
Pilots should pay particular attention to
position orientation while using GPS. Distance and track information are
provided to the next active waypoint, not to a fixed navigation aid. Receivers
may sequence when the pilot is not flying along an active route, such as when
being vectored or deviating for weather, due to the proximity to another
waypoint in the route. This can be prevented by placing the receiver in the
nonsequencing mode. When the receiver is in the nonsequencing mode, bearing
and distance are provided to the selected waypoint and the receiver will not
sequence to the next waypoint in the route until placed back in the auto
sequence mode or the pilot selects a different waypoint. The pilot may have to
compute the ATD to stepdown fixes and other points on overlay approaches, due to
the receiver showing ATD to the next waypoint rather than DME to the VOR or ILS
(k) Impact of Magnetic Variation on PBN
(1) Differences may exist between PBN
systems and the charted magnetic courses on ground-based NAVAID instrument
flight procedures (IFP), enroute charts, approach charts, and Standard
Instrument Departure/Standard Terminal Arrival (SID/STAR) charts. These
differences are due to the magnetic variance used to calculate the magnetic
course. Every leg of an instrument procedure is first computed along a desired
ground track with reference to true north. A magnetic variation correction is
then applied to the true course in order to calculate a magnetic course for
publication. The type of procedure will determine what magnetic variation value
is added to the true course. A ground-based NAVAID IFP applies the facility
magnetic variation of record to the true course to get the charted magnetic
course. Magnetic courses on PBN procedures are calculated two different ways.
SID/STAR procedures use the airport magnetic variation of record, while IFR
enroute charts use magnetic reference bearing. PBN systems make a correction to
true north by adding a magnetic variation calculated with an algorithm based on
aircraft position, or by adding the magnetic variation coded in their
navigational database. This may result in the PBN system and the procedure
designer using a different magnetic variation, which causes the magnetic course
by the PBN system and the magnetic course
on the IFP plate to be different. It is important to understand, however,
that PBN systems, (with the exception of VOR/DME RNAV equipment) navigate by
reference to true north and display magnetic course only for pilot reference. As
such, a properly functioning
PBN system, containing a
current and accurate navigational database, should fly the correct
ground track for any loaded instrument procedure, despite differences in
displayed magnetic course that may be attributed to magnetic variation
application. Should significant differences between the approach chart and the
PBN system avionics' application of the navigation database arise, the published
approach chart, supplemented by NOTAMs, holds precedence.
(2) The course
into a waypoint may not always be 180 degrees different from the course leaving
the previous waypoint, due to the PBN system avionics' computation of geodesic
paths, distance between waypoints, and differences in magnetic variation
application. Variations in distances may also occur since PBN system
distance-to-waypoint values are ATDs computed to the next waypoint and the DME
values published on underlying procedures are slant-range distances measured to
the station. This difference increases with aircraft altitude and proximity to
(l) GPS Familiarization
Pilots should practice GPS approaches in
visual meteorological conditions (VMC) until thoroughly proficient with all
aspects of their equipment (receiver and installation) prior to attempting
flight in instrument meteorological conditions (IMC). Pilots should be
proficient in the following areas:
(1) Using the receiver autonomous
integrity monitoring (RAIM) prediction function;
(2) Inserting a DP into the flight
plan, including setting terminal CDI sensitivity, if required, and the
conditions under which terminal RAIM is available for departure;
(3) Programming the destination
(4) Programming and flying the
approaches (especially procedure turns and arcs);
(5) Changing to another approach after
selecting an approach;
(6) Programming and flying “direct”
(7) Programming and flying “routed”
(8) Entering, flying, and exiting
holding patterns, particularly on approaches with a second waypoint
in the holding pattern;
(9) Programming and flying a “route”
from a holding pattern;
(10) Programming and flying an
approach with radar vectors to the intermediate segment;
(11) Indication of the actions
required for RAIM failure both before and after the FAWP; and
(12) Programming a radial and distance
from a VOR (often used in departure instructions).
GPS IFR Equipment Classes/Categories
Nav. Sys. to Prov. RAIM Equiv.
Nonprecision Approach Capable
- GPS sensor and navigation capability.
- GPS sensor data to an integrated navigation system (i.e., FMS, multi-sensor
navigation system, etc.).
- GPS sensor data to an integrated navigation system (as in Class B) which
provides enhanced guidance to an autopilot, or flight director, to reduce flight
tech. errors. Limited to 14 CFR Part 121 or equivalent criteria.
GPS Approval Required/Authorized Use
Installation Approval Required
Operational Approval Required
In Lieu of ADF and/or DME3
Route and Terminal
Route, Terminal, and Approach
1To determine equipment approvals and
limitations, refer to the AFM, AFM supplements, or pilot guides.
2Requires verification of data for
correctness if database is expired.
3Requires current database or
verification that the procedure has not been amended since the expiration of the
4VFR and hand-held GPS systems are not
authorized for IFR navigation, instrument approaches, or as a primary instrument
flight reference. During IFR operations they may be considered only an aid to
5Hand-held receivers require no
approval. However, any aircraft modification to support the hand-held receiver;
i.e., installation of an external antenna or a permanent mounting bracket, does
1-1-19. Wide Area Augmentation
FAA developed the WAAS to improve the accuracy, integrity and
availability of GPS signals. WAAS will allow GPS to be used, as the aviation
navigation system, from takeoff through approach when it is complete. WAAS is a
critical component of the FAA's strategic objective for a seamless satellite
navigation system for civil aviation, improving capacity and safety.
2. The International Civil Aviation
Organization (ICAO) has defined Standards and Recommended Practices (SARPs) for
satellite-based augmentation systems (SBAS) such as WAAS. Japan, India, and
Europe are building similar systems: EGNOS, the European Geostationary
Navigation Overlay System; India's GPS and GeoAugmented Navigation (GAGAN)
system; and Japan's Multifunctional Transport Satellite (MTSAT)based Satellite
Augmentation System (MSAS). The merging of these systems will create an
expansive navigation capability similar to GPS, but with greater accuracy,
availability, and integrity.
3. Unlike traditional ground-based
navigation aids, WAAS will cover a more extensive service area. Precisely
surveyed wide-area reference stations (WRS) are linked to form the U.S. WAAS
network. Signals from the GPS satellites are monitored by these WRSs to
determine satellite clock and ephemeris corrections and to model the propagation
effects of the ionosphere. Each station in the network relays the data to a
wide-area master station (WMS) where the correction information is computed. A
correction message is prepared and uplinked to a geostationary earth orbit
satellite (GEO) via a GEO uplink subsystem (GUS) which is located at the ground
earth station (GES). The message is then broadcast on the same frequency as GPS
(L1, 1575.42 MHz) to WAAS receivers within the broadcast coverage area of the
4. In addition to providing the
correction signal, the WAAS GEO provides an additional pseudorange measurement
to the aircraft receiver, improving the availability of GPS by providing, in
effect, an additional GPS satellite in view. The integrity of GPS is improved
through real-time monitoring, and the accuracy is improved by providing
differential corrections to reduce errors. The performance improvement is
sufficient to enable approach procedures with GPS/WAAS glide paths (vertical
5. The FAA has completed installation
of 3 GEO satellite links, 38 WRSs, 3 WMSs, 6 GES, and the required terrestrial
communications to support the WAAS network including 2 operational control
centers. Prior to the commissioning of the WAAS for public use, the FAA
conducted a series of test and validation activities. Future dual frequency
operations are planned.
6. GNSS navigation, including GPS and
WAAS, is referenced to the WGS-84 coordinate system. It should only be used
where the Aeronautical Information Publications (including electronic data and
aeronautical charts) conform to WGS-84 or equivalent. Other countries' civil
aviation authorities may impose additional limitations on the use of their SBAS
b. Instrument Approach Capabilities
1. A class of approach procedures
which provide vertical guidance, but which do not meet the ICAO Annex 10
requirements for precision approaches has been developed to support satellite
navigation use for aviation applications worldwide. These procedures are not
precision and are referred to as Approach with Vertical Guidance (APV), are
defined in ICAO Annex 6, and include approaches such as the LNAV/VNAV and
localizer performance with vertical guidance (LPV). These approaches provide
vertical guidance, but do not meet the more stringent standards of a precision
approach. Properly certified WAAS receivers will be able to fly to LPV minima and LNAV/VNAV minima, using a WAAS electronic glide path,
which eliminates the errors that can be introduced by using Barometric
2. LPV minima takes advantage of the
high accuracy guidance and increased integrity provided by WAAS. This WAAS
generated angular guidance allows the use of the same TERPS approach criteria
used for ILS approaches. LPV minima may have a decision altitude as low as 200
feet height above touchdown with visibility minimums as low as 1/2
mile, when the terrain and airport infrastructure support the lowest minima. LPV
minima is published on the RNAV (GPS) approach charts (see Paragraph
Approach Procedure Charts).
3. A different
WAASbased line of minima, called Localizer Performance (LP) is being added in
locations where the terrain or obstructions do not allow publication of
vertically guided LPV minima. LP takes advantage of the angular lateral guidance
and smaller position errors provided by WAAS to provide a lateral only procedure
similar to an ILS Localizer. LP procedures may provide lower minima than a LNAV
procedure due to the narrower obstacle clearance surface.
WAAS receivers certified prior to TSO-C145b and TSO-C146b, even if they have LPV
capability, do not contain LP capability unless the receiver has been upgraded.
Receivers capable of flying LP procedures must contain a statement in the
Aircraft Flight Manual (AFM), AFM Supplement, or Approved Supplemental Flight
Manual stating that the receiver has LP capability, as well as the capability
for the other WAAS and GPS approach procedure types.
4. WAAS provides a level of service
that supports all phases of flight, including RNAV (GPS) approaches to LNAV, LP,
LNAV/VNAV, and LPV lines of minima, within system coverage. Some locations close
to the edge of the coverage may have a lower availability of vertical guidance.
c. General Requirements
1. WAAS avionics must be certified in
accordance with Technical Standard Order (TSO) TSO-C145(), Airborne Navigation
Sensors Using the (GPS) Augmented by the Wide Area Augmentation System (WAAS);
or TSO-C146(), Stand-Alone Airborne Navigation Equipment Using the Global
Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS),
and installed in accordance with Advisory Circular (AC) 20-138(),
Airworthiness Approval of Positioning and Navigation Systems.
2. GPS/WAAS operation must be
conducted in accordance with the FAA-approved aircraft flight manual (AFM) and
flight manual supplements. Flight manual supplements will state the level of
approach procedure that the receiver supports. IFR approved WAAS receivers
support all GPS only operations as long as lateral capability at the appropriate
level is functional. WAAS monitors both GPS and WAAS satellites and provides
3. GPS/WAAS equipment is inherently
capable of supporting oceanic and remote operations if the operator obtains a
fault detection and exclusion (FDE) prediction program.
4. Air carrier and commercial
operators must meet the appropriate provisions of their approved operations
5. Prior to GPS/WAAS IFR operation,
the pilot must review appropriate Notices to Airmen (NOTAMs) and aeronautical
information. This information is available on request from a Flight Service
Station. The FAA will provide NOTAMs to advise pilots of the status of the WAAS
and level of service available.
(a) The term MAY NOT BE AVBL is used
in conjunction with WAAS NOTAMs and indicates that due to ionospheric
conditions, lateral guidance may still be available when vertical guidance is
unavailable. Under certain conditions, both lateral and vertical guidance may be
unavailable. This NOTAM language is an advisory to pilots indicating the
expected level of WAAS service (LNAV/VNAV, LPV, LP) may not be available.
!FDC FDC NAV WAAS VNAV/LPV/LP MINIMA MAY NOT BE AVBL 13061113301306141930EST
!FDC FDC NAV WAAS VNAV/LPV MINIMA NOT AVBL, WAAS LP MINIMA MAY NOT BE AVBL
WAAS MAY NOT BE AVBL NOTAMs are predictive in
nature and published for flight planning purposes. Upon commencing an approach
at locations NOTAMed WAAS MAY NOT BE AVBL, if the WAAS avionics indicate
LNAV/VNAV or LPV service is available, then vertical guidance may be used to
complete the approach using the displayed level of service. Should an outage
occur during the approach, reversion to LNAV minima or an alternate instrument
approach procedure may be required. When GPS testing NOTAMS are published and
testing is actually occurring, Air Traffic Control will advise pilots requesting
or cleared for a GPS or RNAV (GPS) approach that GPS may not be available and
request intentions. If pilots have reported GPS anomalies, Air Traffic Control
will request the pilot's intentions and/or clear the pilot for an alternate
approach, if available and operational.
(b) WAAS areawide NOTAMs are
originated when WAAS assets are out of service and impact the service area.
Area-wide WAAS NOT AVAILABLE (AVBL) NOTAMs indicate loss or malfunction of the
WAAS system. In flight, Air Traffic Control will advise pilots requesting a GPS
or RNAV (GPS) approach of WAAS NOT AVBL NOTAMs if not contained in the ATIS
For unscheduled loss of signal or service, an example NOTAM is: !FDC FDC NAV
WAAS NOT AVBL 1311160600- 1311191200EST.
For scheduled loss of signal or service, an example NOTAM is: !FDC FDC NAV WAAS
NOT AVBL 1312041015 1312082000EST.
(c) Site-specific WAAS MAY NOT BE AVBL
NOTAMs indicate an expected level of service; for example, LNAV/VNAV, LP, or LPV
may not be available. Pilots must request site-specific WAAS NOTAMs during
flight planning. In flight, Air Traffic Control will not advise pilots of WAAS
MAY NOT BE AVBL NOTAMs.
Though currently unavailable, the FAA is updating its prediction tool software
to provide this siteservice in the future.
(d) Most of North America has
redundant coverage by two or more geostationary satellites. One exception is the
northern slope of Alaska. If there is a problem with the satellite providing
coverage to this area, a NOTAM similar to the following example will be issued:
!FDC 4/3406 (PAZA A0173/14) ZAN NAV WAAS SIGNAL MAY NOT BE AVBL NORTH OF
LINE FROM 7000N150000W TO 6400N16400W. RMK WAAS USERS SHOULD CONFIRM RAIM
AVAILABILITY FOR IFR OPERATIONS IN THIS AREA. TROUTES IN THIS SECTOR NOT AVBL.
ANY REQUIRED ALTERNATE AIRPORT IN THIS AREA MUST HAVE AN APPROVED INSTRUMENT
APPROACH PROCEDURE OTHER THAN GPS THAT IS ANTICIPATED TO BE OPERATIONAL AND
AVAILABLE AT THE ESTIMATED TIME OF ARRIVAL AND WHICH THE AIRCRAFT IS EQUIPPED TO
FLY. 14060308121406050812EST .
6. When GPS-testing NOTAMS are
published and testing is actually occurring, Air Traffic Control will advise
pilots requesting or cleared for a GPS or RNAV (GPS) approach that GPS may not
be available and request intentions. If pilots have reported GPS anomalies, Air
Traffic Control will request the pilot's intentions and/or clear the pilot for
an alternate approach, if available and operational.
Here is an example of a GPS testing NOTAM:
!GPS 06/001 ZAB NAV GPS (INCLUDING WAAS, GBAS, AND ADSB) MAY NOT BE
AVAILABLE WITHIN A 468NM RADIUS CENTERED AT 330702N1062540W (TCS 093044)
FL400UNL DECREASING IN AREA WITH A DECREASE IN ALTITUDE DEFINED AS: 425NM
RADIUS AT FL250, 360NM RADIUS AT 10000FT, 354NM RADIUS AT 4000FT AGL, 327NM
RADIUS AT 50FT AGL. 14060703001406071200.
7. When the approach chart is
annotated with the
symbol, site-specific WAAS MAY NOT BE AVBL NOTAMs or Air Traffic advisories are
not provided for outages in WAAS LNAV/VNAV and LPV vertical service. Vertical
outages may occur daily at these locations due to being close to the edge of
WAAS system coverage. Use LNAV or circling minima for flight planning at these
locations, whether as a destination or alternate. For flight operations at these
locations, when the WAAS avionics indicate that LNAV/VNAV or LPV service is
available, then the vertical guidance may be used to complete the approach using
the displayed level of service. Should an outage occur during the procedure,
reversion to LNAV minima may be required.
Area-wide WAAS NOT AVBL NOTAMs apply to all airports in the WAAS NOT AVBL area
designated in the NOTAM, including approaches at airports where an approach
chart is annotated with the
8. GPS/WAAS was developed to be used
within GEO coverage over North America without the need for other radio
navigation equipment appropriate to the route of flight to be flown. Outside the
WAAS coverage or in the event of a WAAS failure, GPS/WAAS equipment reverts to
GPS-only operation and satisfies the requirements for basic GPS equipment. (See
paragraph 1-1-18 for these requirements).
9. Unlike TSO-C129 avionics, which
were certified as a supplement to other means of navigation, WAAS avionics are
evaluated without reliance on other navigation systems. As such, installation of
WAAS avionics does not require the aircraft to have other equipment appropriate
to the route to be flown. (See paragraph 1-1-18 d
for more information on equipment requirements.)
(a) Pilots with WAAS receivers may
flight plan to use any instrument approach procedure authorized for use with
their WAAS avionics as the planned approach at a required alternate, with
the following restrictions. When using WAAS at an alternate airport, flight
planning must be based on flying the RNAV (GPS) LNAV or circling minima line,
or minima on a GPS approach procedure, or conventional approach procedure with
“or GPS” in the title. Code of Federal Regulation (CFR) Part 91 non-precision
weather requirements must be used for planning. Upon arrival at an alternate,
when the WAAS navigation system indicates that LNAV/VNAV or LPV service is
available, then vertical guidance may be used to complete the approach using the
displayed level of service. The FAA has begun removing the
NA (Alternate Minimums Not Authorized) symbol from select RNAV (GPS) and
GPS approach procedures so they may be used by approach approved WAAS receivers
at alternate airports. Some approach procedures will still require the
NA for other reasons, such as no weather reporting, so it cannot be
removed from all procedures. Since every procedure must be individually
evaluated, removal of the
from RNAV (GPS) and GPS procedures will take some time.
Properly trained and approved, as required, TSOC145() and TSOC146() equipped
users (WAAS users) with and using approved baroVNAV equipment may plan for
LNAV/VNAV DA at an alternate airport. Specifically authorized WAAS users with
and using approved baroVNAV equipment may also plan for RNP 0.3 DA at the
alternate airport as long as the pilot has verified RNP availability through an
approved prediction program.
d. Flying Procedures with WAAS
1. WAAS receivers support all basic
GPS approach functions and provide additional capabilities. One of the major
improvements is the ability to generate glide path guidance, independent of
ground equipment or barometric aiding. This eliminates several problems such as
hot and cold temperature effects, incorrect altimeter setting, or lack of a
local altimeter source. It also allows approach procedures to be built without
the cost of installing ground stations at each airport or runway. Some approach
certified receivers may only generate a glide path with performance similar to
Baro-VNAV and are only approved to fly the LNAV/VNAV line of minima on the RNAV
(GPS) approach charts. Receivers with additional capability (including faster
update rates and smaller integrity limits) are approved to fly the LPV line of
minima. The lateral integrity changes dramatically from the 0.3 NM (556 meter)
limit for GPS, LNAV, and LNAV/VNAV approach mode, to 40 meters for LPV. It also
provides vertical integrity monitoring, which bounds the vertical error to 50
meters for LNAV/VNAV and LPVs with minima of 250' or above, and bounds the
vertical error to 35 meters for LPVs with minima below 250'.
2. When an approach procedure is
selected and active, the receiver will notify the pilot of the most accurate
level of service supported by the combination of the WAAS signal, the receiver,
and the selected approach, using the naming conventions on the minima lines of
the selected approach procedure. For example, if an approach is published with
LPV minima and the receiver is only certified for LNAV/VNAV, the equipment would
indicate “LNAV/VNAV available,” even though the WAAS signal would support LPV.
If flying an existing LNAV/VNAV procedure with no LPV minima, the receiver will
notify the pilot “LNAV/VNAV available,” even if the receiver is certified for
LPV and the signal supports LPV. If the signal does not support vertical
guidance on procedures with LPV and/or LNAV/VNAV minima, the receiver
annunciation will read “LNAV available.” On lateral only procedures with LP and
LNAV minima the receiver will indicate “LP available” or “LNAV available” based
on the level of lateral service available. Once the level of service
notification has been given, the receiver will operate in this mode for the
duration of the approach procedure, unless that level of service becomes
unavailable. The receiver cannot change back to a more accurate level of service
until the next time an approach is activated.
Receivers do not “fail down” to lower levels of service once the approach has
been activated. If only the vertical off flag appears, the pilot may elect to
use the LNAV minima if the rules under which the flight is operating allow
changing the type of approach being flown after commencing the procedure. If the
lateral integrity limit is exceeded on an LP approach, a missed approach will be
necessary since there is no way to reset the lateral alarm limit while the
approach is active.
3. Another additional feature of WAAS
receivers is the ability to exclude a bad GPS signal and continue operating
normally. This is normally accomplished by the WAAS correction information.
Outside WAAS coverage or when WAAS is not available, it is accomplished through
a receiver algorithm called FDE. In most cases this operation will be invisible
to the pilot since the receiver will continue to operate with other available
satellites after excluding the “bad” signal. This capability increases the
reliability of navigation.
4. Both lateral
and vertical scaling for the LNAV/VNAV and LPV approach procedures are different
than the linear scaling of basic GPS. When the complete published procedure is
flown, ±1 NM linear scaling is provided until two (2) NM prior to the FAF, where
the sensitivity increases to be similar to the angular scaling of an ILS. There
are two differences in the WAAS scaling and ILS: 1) on long final approach
segments, the initial scaling will be ±0.3 NM to achieve equivalent performance
to GPS (and better than ILS, which is less sensitive far from the runway); 2)
close to the runway threshold, the scaling changes to linear instead of
continuing to become more sensitive. The width of the final approach course is
tailored so that the total width is usually 700 feet at the runway threshold.
Since the origin point of the lateral splay for the angular portion of the final
is not fixed due to antenna placement like localizer, the splay angle can remain
fixed, making a consistent width of final for aircraft being vectored onto the
final approach course on different length runways. When the complete published
procedure is not flown, and instead the aircraft needs to capture the extended
final approach course similar to ILS, the vector to final (VTF) mode is used.
Under VTF, the scaling is linear at ± NM until the point where the ILS angular
splay reaches a width of ±1 NM regardless of the distance from the FAWP.
5. The WAAS scaling is also different
than GPS TSO-C129() in the initial portion of the missed approach. Two
differences occur here. First, the scaling abruptly changes from the approach
scaling to the missed approach scaling, at approximately the departure end of
the runway or when the pilot selects missed approach guidance rather than
ramping as GPS does. Second, when the first leg of the missed approach is a
Track to Fix (TF) leg aligned within 3 degrees of the inbound course, the
receiver will change to 0.3 NM linear sensitivity until the turn initiation
point for the first waypoint in the missed approach procedure, at which time it
will abruptly change to terminal (±1 NM) sensitivity. This allows the
elimination of close in obstacles in the early part of the missed approach that
may otherwise cause the DA to be raised.
6. There are two ways to select the
final approach segment of an instrument approach. Most receivers use menus where
the pilot selects the airport, the runway, the specific approach procedure and
finally the IAF, there is also a channel number selection method. The pilot
enters a unique 5-digit number provided on the approach chart, and the receiver
recalls the matching final approach segment from the aircraft database. A list
of information including the available IAFs is displayed and the pilot selects
the appropriate IAF. The pilot should confirm that the correct final approach
segment was loaded by cross checking the Approach ID, which is also provided on
the approach chart.
7. The Along-Track Distance (ATD)
during the final approach segment of an LNAV procedure (with a minimum descent
altitude) will be to the MAWP. On LNAV/VNAV and LPV approaches to a decision
altitude, there is no missed approach waypoint so the along-track distance is
displayed to a point normally located at the runway threshold. In most cases,
the MAWP for the LNAV approach is located on the runway threshold at the
centerline, so these distances will be the same. This distance will always vary
slightly from any ILS DME that may be present, since the ILS DME is located
further down the runway. Initiation of the missed approach on the LNAV/VNAV and
LPV approaches is still based on reaching the decision altitude without any of
the items listed in 14 CFR Section 91.175 being visible, and must not be delayed
while waiting for the ATD to reach zero. The WAAS receiver, unlike a GPS
receiver, will automatically sequence past the MAWP if the missed approach
procedure has been designed for RNAV. The pilot may also select missed approach
prior to the MAWP; however, navigation will continue to the MAWP prior to
waypoint sequencing taking place.
1-1-20. Ground Based Augmentation System (GBAS) Landing
GLS provides precision navigation guidance for exact alignment and descent of
aircraft on approach to a runway. It provides differential augmentation to the
Global Navigation Satellite System (GNSS).
GBAS is the ICAO term for Local Area Augmentation System (LAAS).
was developed as an “ILS look-alike” system from the pilot perspective. LAAS is
based on GPS signals augmented by ground equipment and has been developed to
provide GLS precision approaches similar to ILS at airfields.
provides guidance similar to ILS approaches for the final approach segment;
portions of the GLS approach prior to and after the final approach segment will
be based on Area Navigation (RNAV) or Required Navigation Performance (RNP).
equipment consists of a GBAS Ground Facility (GGF), four reference stations, a
VHF Data Broadcast (VDB) uplink antenna, and an aircraft GBAS receiver.
will select the five digit GBAS channel number of the associated approach within
the Flight Management System (FMS) menu or manually select the five digits
(system dependent). Selection of the GBAS channel number also tunes the VDB.
procedure selection, confirmation that the correct LAAS procedure is loaded can
be accomplished by cross checking the charted Reference Path Indicator (RPI) or
approach ID with the cockpit displayed RPI or audio identification of the RPI
with Morse Code (for some systems).
pilot will fly the GLS approach using the same techniques as an ILS, once
selected and identified.
1-1-21. Precision Approach Systems other than ILS and GLS
Approval and use of precision approach systems
other than ILS and GLS require the issuance of special instrument approach
b. Special Instrument
instrument approach procedures must be issued to the aircraft operator if pilot
training, aircraft equipment, and/or aircraft performance is different than
published procedures. Special instrument approach procedures are not distributed
for general public use. These procedures are issued to an aircraft operator when
the conditions for operations approval are satisfied.
aviation operators requesting approval for special procedures should contact the
local Flight Standards District Office to obtain a letter of authorization. Air
carrier operators requesting approval for use of special procedures should
contact their Certificate Holding District Office for authorization through
their Operations Specification.
c. Transponder Landing
TLS is designed to provide approach guidance utilizing existing airborne ILS
localizer, glide slope, and transponder equipment.
equipment consists of a transponder interrogator, sensor arrays to detect
lateral and vertical position, and ILS frequency transmitters. The TLS detects
the aircraft's position by interrogating its transponder. It then broadcasts ILS
frequency signals to guide the aircraft along the desired approach path.
instrument approach procedures are designated Special Instrument Approach
Procedures. Special aircrew training is required. TLS ground equipment provides
approach guidance for only one aircraft at a time. Even though the TLS signal is
received using the ILS receiver, no fixed course or glidepath is generated. The
concept of operation is very similar to an air traffic controller providing
radar vectors, and just as with radar vectors, the guidance is valid only for
the intended aircraft. The TLS ground equipment tracks one aircraft, based on
its transponder code, and provides correction signals to course and glidepath
based on the position of the tracked aircraft. Flying the TLS corrections
computed for another aircraft will not provide guidance relative to the
approach; therefore, aircrews must not use the TLS signal for navigation unless
they have received approach clearance and completed the required coordination
with the TLS ground equipment operator. Navigation fixes based on conventional
NAVAIDs or GPS are provided in the special instrument approach procedure to
allow aircrews to verify the TLS guidance.
d. Special Category I Differential GPS (SCAT-I DGPS)
SCAT-I DGPS is designed to provide approach guidance by broadcasting
differential correction to GPS.
DGPS procedures require aircraft equipment and pilot training.
equipment consists of GPS receivers and a VHF digital radio transmitter. The
SCAT-I DGPS detects the position of GPS satellites relative to GPS receiver
equipment and broadcasts differential corrections over the VHF digital radio.
I Ground Based Augmentation System (GBAS) will displace SCAT-I DGPS as the
public use service.
Instrument Approach Procedures.