Section 4. ATC Clearances and Aircraft Separation
a. A clearance issued by ATC is predicated on
known traffic and known physical airport conditions.
An ATC clearance means an authorization by ATC,
for the purpose of preventing collision between
known aircraft, for an aircraft to proceed under
specified conditions within controlled airspace. IT IS
NOT AUTHORIZATION FOR A PILOT TO
DEVIATE FROM ANY RULE, REGULATION, OR
MINIMUM ALTITUDE NOR TO CONDUCT
UNSAFE OPERATION OF THE AIRCRAFT.
b. 14 CFR Section 91.3(a) states: “The pilot-in-command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.” If ATC issues a clearance that would cause a pilot to deviate from a rule or regulation, or in the pilot's opinion, would place the aircraft in jeopardy, IT IS THE PILOT'S RESPONSIBILITY TO REQUEST AN AMENDED CLEARANCE. Similarly, if a pilot prefers to follow a different course of action, such as make a 360 degree turn for spacing to follow traffic when established in a landing or approach sequence, land on a different runway, takeoff from a different intersection, takeoff from the threshold instead of an intersection, or delay operation, THE PILOT IS EXPECTED TO INFORM ATC ACCORDINGLY. When the pilot requests a different course of action, however, the pilot is expected to cooperate so as to preclude disruption of traffic flow or creation of conflicting patterns. The pilot is also expected to use the appropriate aircraft call sign to acknowledge all ATC clearances, frequency changes, or advisory information.
c. Each pilot who deviates from an ATC clearance
in response to a Traffic Alert and Collision Avoidance
System resolution advisory must notify ATC of that
deviation as soon as possible.
Pilot/Controller Glossary Term- Traffic Alert and Collision Avoidance
d. When weather conditions permit, during the
time an IFR flight is operating, it is the direct
responsibility of the pilot to avoid other aircraft since
VFR flights may be operating in the same area
without the knowledge of ATC. Traffic clearances
provide standard separation only between IFR
4-4-2. Clearance Prefix
A clearance, control information, or a response to a
request for information originated by an ATC facility
and relayed to the pilot through an air-to-ground
communication station will be prefixed by “ATC
clears,” “ATC advises,” or “ATC requests.”
4-4-3. Clearance Items
ATC clearances normally contain the following:
a. Clearance Limit. The traffic clearance issued
prior to departure will normally authorize flight to the
airport of intended landing. Many airports and
associated NAVAIDs are collocated with the same
name and/or identifier, so care should be exercised to
ensure a clear understanding of the clearance limit.
When the clearance limit is the airport of intended
landing, the clearance should contain the airport
name followed by the word “airport.” Under certain
conditions, a clearance limit may be a NAVAID or
other fix. When the clearance limit is a NAVAID,
intersection, or waypoint and the type is known, the
clearance should contain type. Under certain
conditions, at some locations a short-range clearance
procedure is utilized whereby a clearance is issued to
a fix within or just outside of the terminal area and
pilots are advised of the frequency on which they will
receive the long-range clearance direct from the
b. Departure Procedure. Headings to fly and
altitude restrictions may be issued to separate a
departure from other air traffic in the terminal area.
Where the volume of traffic warrants, DPs have been
AIM, Abbreviated IFR Departure Clearance (Cleared. . .as Filed)
Procedures, Paragraph 5-2-5.
AIM, Instrument Departure Procedures (DP) - Obstacle Departure
Procedures (ODP) and Standard Instrument Departures (SID),
c. Route of Flight.
1. Clearances are normally issued for the
altitude or flight level and route filed by the pilot.
However, due to traffic conditions, it is frequently
necessary for ATC to specify an altitude or flight level
or route different from that requested by the pilot. In
addition, flow patterns have been established in
certain congested areas or between congested areas
whereby traffic capacity is increased by routing all
traffic on preferred routes. Information on these flow
patterns is available in offices where preflight
briefing is furnished or where flight plans are
2. When required, air traffic clearances include
data to assist pilots in identifying radio reporting
points. It is the responsibility of pilots to notify ATC
immediately if their radio equipment cannot receive
the type of signals they must utilize to comply with
d. Altitude Data.
1. The altitude or flight level instructions in an
ATC clearance normally require that a pilot
“MAINTAIN” the altitude or flight level at which the
flight will operate when in controlled airspace.
Altitude or flight level changes while en route should
be requested prior to the time the change is desired.
2. When possible, if the altitude assigned is
different from the altitude requested by the pilot, ATC
will inform the pilot when to expect climb or descent
clearance or to request altitude change from another
facility. If this has not been received prior to crossing
the boundary of the ATC facility's area and
assignment at a different altitude is still desired, the
pilot should reinitiate the request with the next
3. The term “cruise” may be used instead of
“MAINTAIN” to assign a block of airspace to a pilot
from the minimum IFR altitude up to and including
the altitude specified in the cruise clearance. The pilot
may level off at any intermediate altitude within this
block of airspace. Climb/descent within the block is
to be made at the discretion of the pilot. However,
once the pilot starts descent and verbally reports
leaving an altitude in the block, the pilot may not
return to that altitude without additional ATC
Pilot/Controller Glossary Term- Cruise.
e. Holding Instructions.
1. Whenever an aircraft has been cleared to a fix
other than the destination airport and delay is
expected, it is the responsibility of the ATC controller
to issue complete holding instructions (unless the
pattern is charted), an EFC time, and a best estimate
of any additional en route/terminal delay.
2. If the holding pattern is charted and the
controller doesn't issue complete holding instructions, the pilot is expected to hold as depicted on the
appropriate chart. When the pattern is charted, the
controller may omit all holding instructions except
the charted holding direction and the statement
AS PUBLISHED, e.g., “HOLD EAST AS
PUBLISHED.” Controllers must always issue
complete holding instructions when pilots request
Only those holding patterns depicted on U.S. government
or commercially produced charts which meet FAA
requirements should be used.
3. If no holding pattern is charted and holding
instructions have not been issued, the pilot should ask
ATC for holding instructions prior to reaching the fix.
This procedure will eliminate the possibility of an
aircraft entering a holding pattern other than that
desired by ATC. If unable to obtain holding
instructions prior to reaching the fix (due to
frequency congestion, stuck microphone, etc.), hold
in a standard pattern on the course on which you
approached the fix and request further clearance as
soon as possible. In this event, the altitude/flight level
of the aircraft at the clearance limit will be protected
so that separation will be provided as required.
4. When an aircraft is 3 minutes or less from a
clearance limit and a clearance beyond the fix has not
been received, the pilot is expected to start a speed
reduction so that the aircraft will cross the fix,
initially, at or below the maximum holding airspeed.
5. When no delay is expected, the controller
should issue a clearance beyond the fix as soon as
possible and, whenever possible, at least 5 minutes
before the aircraft reaches the clearance limit.
6. Pilots should report to ATC the time and
altitude/flight level at which the aircraft reaches the
clearance limit and report leaving the clearance limit.
In the event of two-way communications failure, pilots are
required to comply with 14 CFR Section 91.185.
4-4-4. Amended Clearances
a. Amendments to the initial clearance will be
issued at any time an air traffic controller deems such
action necessary to avoid possible confliction
between aircraft. Clearances will require that a flight
“hold” or change altitude prior to reaching the point
where standard separation from other IFR traffic
would no longer exist.
Some pilots have questioned this action and requested
“traffic information” and were at a loss when the reply
indicated “no traffic report.” In such cases the controller
has taken action to prevent a traffic confliction which
would have occurred at a distant point.
b. A pilot may wish an explanation of the handling
of the flight at the time of occurrence; however,
controllers are not able to take time from their
immediate control duties nor can they afford to
overload the ATC communications channels to
furnish explanations. Pilots may obtain an explanation by directing a letter or telephone call to the chief
controller of the facility involved.
c. Pilots have the privilege of requesting a
different clearance from that which has been issued
by ATC if they feel that they have information which
would make another course of action more
practicable or if aircraft equipment limitations or
company procedures forbid compliance with the
4-4-5. Coded Departure Route (CDR)
a. CDRs provide air traffic control a rapid means
to reroute departing aircraft when the filed route is
constrained by either weather or congestion.
b. CDRs consist of an eight-character designator
that represents a route of flight. The first three
alphanumeric characters represent the departure
airport, characters four through six represent the
arrival airport, and the last two characters are chosen
by the overlying ARTCC. For example, PITORDN1
is an alternate route from Pittsburgh to Chicago.
Participating aircrews may then be re-cleared by air
traffic control via the CDR abbreviated clearance,
c. CDRs are updated on the 56 day charting cycle.
Participating aircrews must ensure that their CDR is
d. Traditionally, CDRs have been used by air
transport companies that have signed a Memorandum
of Agreement with the local air traffic control facility.
General aviation customers who wish to participate in
the program may now enter “CDR Capable” in the
remarks section of their flight plan.
e. When “CDR Capable” is entered into the
remarks section of the flight plan the general aviation
customer communicates to ATC the ability to decode
the current CDR into a flight plan route and the
willingness to fly a different route than that which
4-4-6. Special VFR Clearances
a. An ATC clearance must be obtained prior to
operating within a Class B, Class C, Class D, or
Class E surface area when the weather is less than that
required for VFR flight. A VFR pilot may request and
be given a clearance to enter, leave, or operate within
most ClassD and Class E surface areas and some
Class B and Class C surface areas in special VFR
conditions, traffic permitting, and providing such
flight will not delay IFR operations. All special VFR
flights must remain clear of clouds. The visibility
requirements for special VFR aircraft (other than
1. At least 1 statute mile flight visibility for
operations within Class B, Class C, Class D, and
Class E surface areas.
2. At least 1 statute mile ground visibility if
taking off or landing. If ground visibility is not
reported at that airport, the flight visibility must be at
least 1 statute mile.
3. The restrictions in subparagraphs 1 and 2 do
not apply to helicopters. Helicopters must remain
clear of clouds and may operate in Class B, Class C,
Class D, and Class E surface areas with less than
1 statute mile visibility.
b. When a control tower is located within the
Class B, Class C, or Class D surface area, requests for
clearances should be to the tower. In a Class E surface
area, a clearance may be obtained from the nearest
tower, FSS, or center.
c. It is not necessary to file a complete flight plan
with the request for clearance, but pilots should state
their intentions in sufficient detail to permit ATC to
fit their flight into the traffic flow. The clearance will
not contain a specific altitude as the pilot must remain
clear of clouds. The controller may require the pilot
to fly at or below a certain altitude due to other traffic,
but the altitude specified will permit flight at or above
the minimum safe altitude. In addition, at radar
locations, flights may be vectored if necessary for
control purposes or on pilot request.
The pilot is responsible for obstacle or terrain clearance.
14 CFR Section 91.119, Minimum safe altitudes: General.
d. Special VFR clearances are effective within
Class B, Class C, Class D, and Class E surface areas
only. ATC does not provide separation after an
aircraft leaves the Class B, Class C, Class D, or
Class E surface area on a special VFR clearance.
e. Special VFR operations by fixed-wing aircraft
are prohibited in some Class B and Class C surface
areas due to the volume of IFR traffic. A list of these
Class B and Class C surface areas is contained in
14 CFR Part 91, Appendix D, Section 3. They are
also depicted on sectional aeronautical charts.
f. ATC provides separation between Special VFR
flights and between these flights and other IFR
g. Special VFR operations by fixed-wing aircraft
are prohibited between sunset and sunrise unless the
pilot is instrument rated and the aircraft is equipped
for IFR flight.
h. Pilots arriving or departing an uncontrolled
airport that has automated weather broadcast
capability (ASOS/AWSS/AWOS) should monitor
the broadcast frequency, advise the controller that
they have the “one-minute weather” and state
intentions prior to operating within the Class B, Class
C, Class D, or Class E surface areas.
Pilot/Controller Glossary Term- One-minute Weather.
4-4-7. Pilot Responsibility upon Clearance
a. Record ATC clearance. When conducting an
IFR operation, make a written record of your
clearance. The specified conditions which are a part
of your air traffic clearance may be somewhat
different from those included in your flight plan.
Additionally, ATC may find it necessary to ADD
conditions, such as particular departure route. The
very fact that ATC specifies different or additional
conditions means that other aircraft are involved in
the traffic situation.
b. ATC Clearance/Instruction Readback.
Pilots of airborne aircraft should read back
those parts of ATC clearances and instructions
containing altitude assignments, vectors, or runway
assignments as a means of mutual verification. The
read back of the “numbers" serves as a double check
between pilots and controllers and reduces the kinds
of communications errors that occur when a number
is either “misheard" or is incorrect.
1. Include the aircraft identification in all
readbacks and acknowledgments. This aids controllers in determining that the correct aircraft received
the clearance or instruction. The requirement to
include aircraft identification in all readbacks and
acknowledgements becomes more important as
frequency congestion increases and when aircraft
with similar call signs are on the same frequency.
“Climbing to Flight Level three three zero, United Twelve"
or “November Five Charlie Tango, roger, cleared to land
runway nine left."
2. Read back altitudes, altitude restrictions, and
vectors in the same sequence as they are given in the
clearance or instruction.
3. Altitudes contained in charted procedures,
such as DPs, instrument approaches, etc., should not
be read back unless they are specifically stated by the
4. Initial read back of a taxi, departure or landing
clearance should include the runway assignment,
including left, right, center, etc. if applicable.
c. It is the responsibility of the pilot to accept or
refuse the clearance issued.
4-4-8. IFR Clearance VFR-on-top
a. A pilot on an IFR flight plan operating in VFR
weather conditions, may request VFR-on-top in lieu
of an assigned altitude. This permits a pilot to select
an altitude or flight level of their choice (subject to
any ATC restrictions.)
b. Pilots desiring to climb through a cloud, haze,
smoke, or other meteorological formation and then
either cancel their IFR flight plan or operate
VFR-on-top may request a climb to VFR-on-top. The ATC authorization must contain either a top report or
a statement that no top report is available, and a
request to report reaching VFR-on-top. Additionally,
the ATC authorization may contain a clearance limit,
routing and an alternative clearance if VFR-on-top is
not reached by a specified altitude.
c. A pilot on an IFR flight plan, operating in VFR
conditions, may request to climb/descend in VFR
d. ATC may not authorize VFR-on-top/VFR
conditions operations unless the pilot requests the
VFR operation or a clearance to operate in VFR
conditions will result in noise abatement benefits
where part of the IFR departure route does not
conform to an FAA approved noise abatement route
e. When operating in VFR conditions with an ATC
authorization to “maintain VFR-on-top/maintain
VFR conditions” pilots on IFR flight plans must:
1. Fly at the appropriate VFR altitude as
prescribed in 14 CFR Section 91.159.
2. Comply with the VFR visibility and distance
from cloud criteria in 14 CFR Section 91.155 (Basic
VFR Weather Minimums).
3. Comply with instrument flight rules that are
applicable to this flight; i.e., minimum IFR altitudes,
position reporting, radio communications, course to
be flown, adherence to ATC clearance, etc.
Pilots should advise ATC prior to any altitude change to
ensure the exchange of accurate traffic information.
f. ATC authorization to “maintain VFR-on-top” is
not intended to restrict pilots so that they must operate
only above an obscuring meteorological formation
(layer). Instead, it permits operation above, below,
between layers, or in areas where there is no
meteorological obscuration. It is imperative, however, that pilots understand that clearance to operate
“VFR-on-top/VFR conditions” does not imply
cancellation of the IFR flight plan.
g. Pilots operating VFR-on-top/VFR conditions
may receive traffic information from ATC on other
pertinent IFR or VFR aircraft. However, aircraft
operating in Class B airspace/TRSAs must be
separated as required by FAA Order JO 7110.65,
Air Traffic Control.
When operating in VFR weather conditions, it is the pilot's
responsibility to be vigilant so as to see-and-avoid other
h. ATC will not authorize VFR or VFR-on-top
operations in Class A airspace.
AIM, Class A Airspace, Paragraph 3-2-2.
4-4-9. VFR/IFR Flights
A pilot departing VFR, either intending to or needing
to obtain an IFR clearance en route, must be aware of
the position of the aircraft and the relative
terrain/obstructions. When accepting a clearance
below the MEA/MIA/MVA/OROCA, pilots are
responsible for their own terrain/obstruction clearance until reaching the MEA/MIA/MVA/OROCA. If
pilots are unable to maintain terrain/obstruction
clearance, the controller should be advised and pilots
should state their intentions.
OROCA is an off-route altitude which provides obstruction clearance with a 1,000 foot buffer in nonmountainous
terrain areas and a 2,000 foot buffer in designated
mountainous areas within the U.S. This altitude may not
provide signal coverage from ground-based navigational
aids, air traffic control radar, or communications
4-4-10. Adherence to Clearance
a. When air traffic clearance has been obtained
under either visual or instrument flight rules, the
pilot-in-command of the aircraft must not deviate
from the provisions thereof unless an amended
clearance is obtained. When ATC issues a clearance
or instruction, pilots are expected to execute its
provisions upon receipt. ATC, in certain situations,
will include the word “IMMEDIATELY” in a
clearance or instruction to impress urgency of an
imminent situation and expeditious compliance by
the pilot is expected and necessary for safety. The
addition of a VFR or other restriction; i.e., climb or
descent point or time, crossing altitude, etc., does not
authorize a pilot to deviate from the route of flight or
any other provision of the ATC clearance.
b. When a heading is assigned or a turn is
requested by ATC, pilots are expected to promptly
initiate the turn, to complete the turn, and maintain the
new heading unless issued additional instructions.
c. The term “AT PILOT'S DISCRETION”
included in the altitude information of an ATC
clearance means that ATC has offered the pilot the
option to start climb or descent when the pilot wishes,
is authorized to conduct the climb or descent at any
rate, and to temporarily level off at any intermediate
altitude as desired. However, once the aircraft has
vacated an altitude, it may not return to that altitude.
d. When ATC has not used the term “AT PILOT'S
DISCRETION” nor imposed any climb or descent
restrictions, pilots should initiate climb or descent
promptly on acknowledgement of the clearance.
Descend or climb at an optimum rate consistent with
the operating characteristics of the aircraft to
1,000 feet above or below the assigned altitude, and
then attempt to descend or climb at a rate of between
500 and 1,500 fpm until the assigned altitude is
reached. If at anytime the pilot is unable to climb or
descend at a rate of at least 500 feet a minute, advise
ATC. If it is necessary to level off at an intermediate
altitude during climb or descent, advise ATC, except
when leveling off at 10,000 feet MSL on descent, or
2,500 feet above airport elevation (prior to entering a
Class C or Class D surface area), when required for
14 CFR Section 91.117.
Leveling off at 10,000 feet MSL on descent or 2,500 feet
above airport elevation (prior to entering a Class C or
Class D surface area) to comply with 14 CFR
Section 91.117 airspeed restrictions is commonplace.
Controllers anticipate this action and plan accordingly.
Leveling off at any other time on climb or descent may
seriously affect air traffic handling by ATC. Consequently,
it is imperative that pilots make every effort to fulfill the
above expected actions to aid ATC in safely handling and
e. If the altitude information of an ATC
DESCENT clearance includes a provision to
“CROSS (fix) AT” or “AT OR ABOVE/BELOW
(altitude),” the manner in which the descent is
executed to comply with the crossing altitude is at the
pilot's discretion. This authorization to descend at
pilot's discretion is only applicable to that portion of
the flight to which the crossing altitude restriction
applies, and the pilot is expected to comply with the
crossing altitude as a provision of the clearance. Any
other clearance in which pilot execution is optional
will so state “AT PILOT'S DISCRETION.”
1. “United Four Seventeen, descend and maintain
1. The pilot is expected to commence descent upon receipt
of the clearance and to descend at the suggested rates until
reaching the assigned altitude of 6,000 feet.
2. “United Four Seventeen, descend at pilot's discretion,
maintain six thousand.”
2. The pilot is authorized to conduct descent within the
context of the term at pilot's discretion as described above.
3. “United Four Seventeen, cross Lakeview V-O-R at or
above Flight Level two zero zero, descend and maintain
3. The pilot is authorized to conduct descent at pilot's
discretion until reaching Lakeview VOR and must comply
with the clearance provision to cross the Lakeview VOR at
or above FL 200. After passing Lakeview VOR, the pilot is
expected to descend at the suggested rates until reaching
the assigned altitude of 6,000 feet.
4. “United Four Seventeen, cross Lakeview V-O-R at
six thousand, maintain six thousand.”
4. The pilot is authorized to conduct descent at pilot's
discretion, however, must comply with the clearance
provision to cross the Lakeview VOR at 6,000 feet.
5. “United Four Seventeen, descend now to Flight
Level two seven zero, cross Lakeview V-O-R at or below
one zero thousand, descend and maintain six thousand.”
5. The pilot is expected to promptly execute and complete
descent to FL 270 upon receipt of the clearance. After
reaching FL 270 the pilot is authorized to descend “at
pilot's discretion” until reaching Lakeview VOR. The pilot
must comply with the clearance provision to cross
Lakeview VOR at or below 10,000 feet. After Lakeview
VOR the pilot is expected to descend at the suggested rates
until reaching 6,000 feet.
6. “United Three Ten, descend now and maintain Flight
Level two four zero, pilot's discretion after reaching Flight
Level two eight zero.”
6. The pilot is expected to commence descent upon receipt
of the clearance and to descend at the suggested rates until
reaching FL 280. At that point, the pilot is authorized to
continue descent to FL 240 within the context of the term
“at pilot's discretion” as described above.
f. In case emergency authority is used to deviate
from provisions of an ATC clearance, the pilot-in-command must notify ATC as soon as possible and obtain an amended clearance. In an emergency situation which does not result in a deviation from the rules prescribed in 14 CFR Part 91 but which requires ATC to give priority to an aircraft, the pilot of such aircraft must, when requested by ATC, make a report within 48 hours of such emergency situation to the manager of that ATC facility.
g. The guiding principle is that the last ATC
clearance has precedence over the previous ATC
clearance. When the route or altitude in a previously
issued clearance is amended, the controller will
restate applicable altitude restrictions. If altitude to
maintain is changed or restated, whether prior to
departure or while airborne, and previously issued
altitude restrictions are omitted, those altitude
restrictions are canceled, including departure procedures and STAR altitude restrictions.
1. A departure flight receives a clearance to destination
airport to maintain FL 290. The clearance incorporates a
DP which has certain altitude crossing restrictions. Shortly
after takeoff, the flight receives a new clearance changing
the maintaining FL from 290 to 250. If the altitude
restrictions are still applicable, the controller restates
2. A departing aircraft is cleared to cross Fluky
Intersection at or above 3,000 feet, Gordonville VOR at or
above 12,000 feet, maintain FL 200. Shortly after
departure, the altitude to be maintained is changed to
FL 240. If the altitude restrictions are still applicable, the
controller issues an amended clearance as follows: “cross
Fluky Intersection at or above three thousand, cross
Gordonville V-O-R at or above one two thousand,
maintain Flight Level two four zero.”
3. An arriving aircraft is cleared to the destination airport
via V45 Delta VOR direct; the aircraft is cleared to cross
Delta VOR at 10,000 feet, and then to maintain 6,000 feet.
Prior to Delta VOR, the controller issues an amended
clearance as follows: “turn right heading one eight zero
for vector to runway three six I-L-S approach, maintain
Because the altitude restriction “cross Delta V-O-R at
10,000 feet” was omitted from the amended clearance, it is
no longer in effect.
h. Pilots of turbojet aircraft equipped with
afterburner engines should advise ATC prior to
takeoff if they intend to use afterburning during their
climb to the en route altitude. Often, the controller
may be able to plan traffic to accommodate a high
performance climb and allow the aircraft to climb to
the planned altitude without restriction.
i. If an “expedite” climb or descent clearance is
issued by ATC, and the altitude to maintain is
subsequently changed or restated without an expedite
instruction, the expedite instruction is canceled.
Expedite climb/descent normally indicates to the
pilot that the approximate best rate of climb/descent
should be used without requiring an exceptional
change in aircraft handling characteristics. Normally
controllers will inform pilots of the reason for an
instruction to expedite.
4-4-11. IFR Separation Standards
a. ATC effects separation of aircraft vertically by
assigning different altitudes; longitudinally by
providing an interval expressed in time or distance
between aircraft on the same, converging, or crossing
courses, and laterally by assigning different flight
b. Separation will be provided between all aircraft
operating on IFR flight plans except during that part
of the flight (outside Class B airspace or a TRSA)
being conducted on a VFR-on-top/VFR conditions
clearance. Under these conditions, ATC may issue
traffic advisories, but it is the sole responsibility of the
pilot to be vigilant so as to see and avoid other aircraft.
c. When radar is employed in the separation of
aircraft at the same altitude, a minimum of 3 miles
separation is provided between aircraft operating
within 40 miles of the radar antenna site, and 5 miles
between aircraft operating beyond 40 miles from the
antenna site. These minima may be increased or
decreased in certain specific situations.
Certain separation standards are increased in the terminal
environment when CENRAP is being utilized.
4-4-12. Speed Adjustments
will issue speed adjustments to pilots of radar-controlled aircraft to achieve
or maintain required or desire spacing.
will express all speed adjustments in terms of knots based on indicated airspeed
(IAS) in 10 knot increments except that at or above FL 240 speeds may be
expressed in terms of Mach numbers in 0.01 increments. The use of Mach numbers
is restricted to turbojet aircraft with Mach meters.
complying with speed adjustments are expected to maintain a speed within plus or
minus 10 knots or 0.02 Mach number of the specified speed.
ATC assigns speed adjustments, it will be in accordance with the following
aircraft operating between FL 280 and 10,000 feet, a speed not less than 250
knots or the equivalent Mach number.
1. On a standard
day the Mach numbers equivalent to 250 knots CAS (subject to minor variations)
an operational advantage will be realized, speeds lower than the recommended
minima may be applied.
arriving turbojet aircraft operating below 10,000 feet:
speed not less than 210 knots, except;
20 flying miles of the airport of intended landing, a speed not less than 170
arriving reciprocating engine or turboprop aircraft within 20 flying miles of
the runway threshold of the airport of intended landing, a speed not less than
aircraft, a speed not less than 230 knots.
engine aircraft, a speed not less than 150 knots.
ATC combines a speed adjustment with a descent clearance, the sequence of
delivery, with the word “then” between, indicates the expected order of
1. Descend and
maintain (altitude); then, reduce speed to (speed).
speed to (speed); then, descend and maintain (altitude).
The maximum speeds below 10,000 feet as established in 14 CFR Section 91.117
still apply. If there is any doubt concerning the manner in which such a
clearance is to be executed, request clarification from ATC.
ATC determines (before an approach clearance is issued) that it is no longer
necessary to apply speed adjustment procedures, they will:
the pilot to “resume normal speed.” Normal speed is used to terminate ATC
assigned speed adjustments on segments where no published speed restrictions
apply. It does not cancel published restrictions on upcoming procedures. This
does not relieve the pilot of those speed restrictions which are applicable to
14 CFR Section 91.117.
(An aircraft is flying a SID with no published speed restrictions. ATC issues a
speed adjustment and instructs the aircraft where the adjustment ends):
“Maintain two two zero knots until BALTR then resume normal speed.”
The ATC assigned speed assignment of two two zero knots would apply until BALTR.
The aircraft would then resume a normal operating speed while remaining in
compliance with 14 CFR Section 91.117.
pilots to “comply with speed restrictions” when the aircraft is joining or
resuming a charted procedure or route with published speed restrictions.
(ATC vectors an aircraft off of a SID to rejoin the procedure at a subsequent
waypoint. When instructing the aircraft to resume the procedure, ATC also wants
the aircraft to comply with the published procedure speed restrictions): “Resume
the SALTY ONE departure. Comply with speed restrictions.”
The phraseology “comply with restrictions” requires compliance with all altitude
and/or speed restrictions depicted on the procedure.
the pilot to “resume published speed.” Resume published speed is issued to
terminate a speed adjustment where speed restrictions are published on a charted
When instructed to “comply with speed restrictions” or to “resume published
speed,” ATC anticipates pilots will begin adjusting speed the minimum distance
necessary prior to a published speed restriction so as to cross the waypoint/fix
at the published speed. Once at the published speed, ATC expects pilots will
maintain the published speed until additional adjustment is required to comply
with further published or ATC assigned speed restrictions or as required to
ensure compliance with 14 CFR Section 91.117.
(An aircraft is flying a SID/STAR with published speed restrictions. ATC issues
a speed adjustment and instructs the aircraft where the adjustment ends):
“Maintain two two zero knots until BALTR then resume published speed.”
The ATC assigned speed assignment of two two zero knots would apply until BALTR.
The aircraft would then comply with the published speed restrictions.
the pilot to “delete speed restrictions” when either ATC assigned or published
speed restrictions on a charted procedure are no longer required.
(An aircraft is flying a SID with published speed restrictions designed to
prevent aircraft overtake on departure. ATC determines there is no conflicting
traffic and deletes the speed restriction): “Delete speed restrictions.”
When deleting published restrictions, ATC must ensure obstacle clearance until
aircraft are established on a route where no published restrictions apply. This
does not relieve the pilot of those speed restrictions which are applicable to
14 CFR Section 91.117.
clearances supersede any prior speed adjustment assignments, and pilots are
expected to make their own speed adjustments as necessary to complete the
approach. However, under certain circumstances, it may be necessary for ATC to
issue further speed adjustments after approach clearance is issued to maintain
separation between successive arrivals. Under such circumstances, previously
issued speed adjustments will be restated if that speed is to be maintained or
additional speed adjustments are requested. Speed adjustments should not be
assigned inside the final approach fix on final or a point 5 miles from the
runway, whichever is closer to the runway.
pilots retain the prerogative of rejecting the application of speed adjustment
by ATC if the minimum safe airspeed for any particular operation is greater than
the speed adjustment.
In such cases, pilots are expected to advise ATC of the speed that will be used.
are reminded that they are responsible for rejecting the application of speed
adjustment by ATC if, in their opinion, it will cause them to exceed the maximum
indicated airspeed prescribed by 14 CFR Section 91.117(a), (c) and (d).
IN SUCH CASES, THE PILOT IS EXPECTED TO SO INFORM ATC.
Pilots operating at or above 10,000 feet MSL who are
issued speed adjustments which exceed 250 knots IAS and are subsequently cleared
below 10,000 feet MSL are expected to comply with 14 CFR Section 91.117(a).
restrictions of 250 knots do not apply to U.S. registered aircraft operating
beyond 12 nautical miles from the coastline within the U.S. Flight Information
Region, in Class E airspace below 10,000 feet MSL. However, in airspace
underlying a Class B airspace area designated for an airport, or in a VFR
corridor designated through such as a Class B airspace area, pilots are expected
to comply with the 200 knot speed limit specified in 14 CFR Section 91.117(c).
operations in a Class C and Class D surface area, ATC is authorized to request
or approve a speed greater than the maximum indicated airspeeds prescribed for
operation within that airspace (14 CFR Section 91.117(b)).
Pilots are expected to comply with the maximum speed of 200 knots when operating
beneath Class B airspace or in a Class B VFR corridor (14 CFR Section 91.117(c)
in communications with the ARTCC or approach control facility, pilots should, as
a good operating practice, state any ATC assigned speed restriction on initial
radio contact associated with an ATC communications frequency change.
4-4-13. Runway Separation
Tower controllers establish the sequence of arriving
and departing aircraft by requiring them to adjust
flight or ground operation as necessary to achieve
proper spacing. They may “HOLD” an aircraft short
of the runway to achieve spacing between it and an
arriving aircraft; the controller may instruct a pilot to
“EXTEND DOWNWIND” in order to establish
spacing from an arriving or departing aircraft. At
times a clearance may include the word “IMMEDIATE.” For example: “CLEARED FOR
IMMEDIATE TAKEOFF.” In such cases “IMMEDIATE” is used for purposes of air traffic separation. It
is up to the pilot to refuse the clearance if, in the pilot's
opinion, compliance would adversely affect the
AIM, Gate Holding due to Departure Delays, Paragraph
4-4-14. Visual Separation
a. Visual separation is a means employed by ATC
to separate aircraft in terminal areas and en route
airspace in the NAS. There are two methods
employed to effect this separation:
1. The tower controller sees the aircraft
involved and issues instructions, as necessary, to
ensure that the aircraft avoid each other.
2. A pilot sees the other aircraft involved and
upon instructions from the controller provides
separation by maneuvering the aircraft to avoid it.
When pilots accept responsibility to maintain visual
separation, they must maintain constant visual
surveillance and not pass the other aircraft until it is
no longer a factor.
Traffic is no longer a factor when during approach phase
the other aircraft is in the landing phase of flight or
executes a missed approach; and during departure or
en route, when the other aircraft turns away or is on a
b. A pilot's acceptance of instructions to follow
another aircraft or provide visual separation from it is
an acknowledgment that the pilot will maneuver the
aircraft as necessary to avoid the other aircraft or to
maintain in-trail separation. In operations conducted
behind heavy jet aircraft, it is also an acknowledgment that the pilot accepts the responsibility for wake
When a pilot has been told to follow another aircraft or to
provide visual separation from it, the pilot should promptly
notify the controller if visual contact with the other aircraft
is lost or cannot be maintained or if the pilot cannot accept
the responsibility for the separation for any reason.
c. Scanning the sky for other aircraft is a key factor
in collision avoidance. Pilots and copilots (or the right
seat passenger) should continuously scan to cover all
areas of the sky visible from the cockpit. Pilots must
develop an effective scanning technique which
maximizes one's visual capabilities. Spotting a
potential collision threat increases directly as more
time is spent looking outside the aircraft. One must
use timesharing techniques to effectively scan the
surrounding airspace while monitoring instruments
d. Since the eye can focus only on a narrow
viewing area, effective scanning is accomplished
with a series of short, regularly spaced eye
movements that bring successive areas of the sky into
the central visual field. Each movement should not
exceed ten degrees, and each area should be observed
for at least one second to enable collision detection.
Although many pilots seem to prefer the method of
horizontal back-and-forth scanning every pilot
should develop a scanning pattern that is not only
comfortable but assures optimum effectiveness.
Pilots should remember, however, that they have a
regulatory responsibility (14 CFR Section 91.113(a))
to see and avoid other aircraft when weather
4-4-15. Use of Visual Clearing Procedures
a. Before Takeoff. Prior to taxiing onto a runway
or landing area in preparation for takeoff, pilots
should scan the approach areas for possible landing
traffic and execute the appropriate clearing maneuvers to provide them a clear view of the approach
b. Climbs and Descents. During climbs and
descents in flight conditions which permit visual
detection of other traffic, pilots should execute gentle
banks, left and right at a frequency which permits
continuous visual scanning of the airspace about
c. Straight and Level. Sustained periods of
straight and level flight in conditions which permit
visual detection of other traffic should be broken at
intervals with appropriate clearing procedures to
provide effective visual scanning.
d. Traffic Pattern. Entries into traffic patterns
while descending create specific collision hazards
and should be avoided.
e. Traffic at VOR Sites. All operators should
emphasize the need for sustained vigilance in the
vicinity of VORs and airway intersections due to the
convergence of traffic.
f. Training Operations. Operators of pilot training programs are urged to adopt the following
1. Pilots undergoing flight instruction at all
levels should be requested to verbalize clearing
procedures (call out “clear” left, right, above, or
below) to instill and sustain the habit of vigilance
2. High-wing airplane. Momentarily raise the
wing in the direction of the intended turn and look.
3. Low-wing airplane. Momentarily lower the
wing in the direction of the intended turn and look.
4. Appropriate clearing procedures should
precede the execution of all turns including
chandelles, lazy eights, stalls, slow flight, climbs,
straight and level, spins, and other combination
4-4-16. Traffic Alert and Collision
Avoidance System (TCAS I & II)
a. TCAS I provides proximity warning only, to
assist the pilot in the visual acquisition of intruder
aircraft. No recommended avoidance maneuvers are
provided nor authorized as a direct result of a TCAS I
warning. It is intended for use by smaller commuter
aircraft holding 10 to 30 passenger seats, and general
b. TCAS II provides traffic advisories (TAs) and
resolution advisories (RAs). Resolution advisories
provide recommended maneuvers in a vertical
direction (climb or descend only) to avoid conflicting
traffic. Airline aircraft, and larger commuter and
business aircraft holding 31 passenger seats or more,
use TCAS II equipment.
1. Each pilot who deviates from an ATC
clearance in response to a TCAS II RA must notify
ATC of that deviation as soon as practicable and
expeditiously return to the current ATC clearance
when the traffic conflict is resolved.
2. Deviations from rules, policies, or clearances
should be kept to the minimum necessary to satisfy a
TCAS II RA.
3. The serving IFR air traffic facility is not
responsible to provide approved standard IFR
separation to an aircraft after a TCAS II RA maneuver
until one of the following conditions exists:
(a) The aircraft has returned to its assigned
altitude and course.
(b) Alternate ATC instructions have been
c. TCAS does not alter or diminish the pilot's basic
authority and responsibility to ensure safe flight.
Since TCAS does not respond to aircraft which are
not transponder equipped or aircraft with a
transponder failure, TCAS alone does not ensure safe
separation in every case.
d. At this time, no air traffic service nor handling
is predicated on the availability of TCAS equipment
in the aircraft.
4-4-17. Traffic Information Service (TIS)
a. TIS provides proximity warning only, to assist
the pilot in the visual acquisition of intruder aircraft.
No recommended avoidance maneuvers are provided
nor authorized as a direct result of a TIS intruder
display or TIS alert. It is intended for use by aircraft
in which TCAS is not required.
b. TIS does not alter or diminish the pilot's basic
authority and responsibility to ensure safe flight.
Since TIS does not respond to aircraft which are not
transponder equipped, aircraft with a transponder
failure, or aircraft out of radar coverage, TIS alone
does not ensure safe separation in every case.
c. At this time, no air traffic service nor handling
is predicated on the availability of TIS equipment in
d. Presently, no air traffic services or handling is
predicated on the availability of an ADS-B cockpit
display. A “traffic-in-sight” reply to ATC must be
based on seeing an aircraft out-the-window, NOT on
the cockpit display.