FAA certified GPS for use over the ocean yet interference has been
experienced precluding the use of GPS. Why is such a system certified?
"GPS avionics used
for primary means of oceanic operations have built in Receiver
Autonomous Integrity Monitoring (RAIM) functions to provide integrity
of navigation. Integrity is the notification of Hazardously Misleading
Information (HMI). In the remote circumstance of a loss of the
integrity function, flight crews can use backup procedures to
insure safe navigation until the RAIM function is restored."
How much will it cost to design approach paths for ILS, MLS, and
GPS? Will it be more expensive or more difficult with one system
A. It should
cost about the same to develop and test approach procedures regardless
of the type of navigation aid used for the approach; roughly $20K
per approach path. Even though the approach path design costs
are basically the same for GPS and ILS/MLS, the real cost benefits
of using GPS lie in the associated user equipment costs and the
expected cost benefits from reduced flight times and fuel consumption
possible with the use of GPS/WAAS. In addition, operations and
maintenance costs of ground-based systems will be significantly
reduced or eliminated when GPS approaches are approved for use
in the NAS.
Given that many NAS users have direct routing capability needed
for Free Flight, to what extent are direct routing benefits being
allocated to WAAS?
A. WAAS implementation and WAAS equipage
will allow the NAS routes to be restructured, resulting in shorter
flight times, saving aircraft operating time and passenger time.
In a study commissioned by the FAA's Air Traffic Organization
and sponsored by the GPS Product Team titled, New England GPS
Alternate Route Study, the average reduction in flight time for
the routes analyzed was one (1) minute. Savings due to universal
WAAS equipage were further analyzed through an Air Traffic study,
The Southern Region Multi-Center Study. This one-minute value
was used to calculate benefits attributed to WAAS as a result
of restructuring NAS routes. For the lower bound of the benefits
to cost ratio the assumption was made that only 30% of all flights
would recognize this benefit. This figure was used because it
is recognized that some aircraft already have direct route capability.
The benefit calculations for savings from reduced flight times
begin in 2006, when it is anticipated overall equipage is great
enough to begin flying the new routes. The benefits for reduced
flight times are only those that will be attributed to future
restructured NAS routes.
How does the FAA plan to use GPS in the future? What are the key
decision factors? When will decisions be made?
A. GPS is an essential element of
the future navigation architecture. Existing ground-based navigation
aids have limited coverage due to terrain, and the majority of
instrument approaches do not have vertical guidance due to the
cost of siting and operating an Instrument Landing System (ILS).
A satellite-based navigation system is needed that can provide
global coverage, regardless of user altitude, and support precision
approach operations at every runway without the need for costly
ground infrastructure. Note that providing vertical guidance on
an approach reduces the risk of controlled flight into terrain
(CFIT) significantly. This satellite-based navigation system must
also be global, so that the level of safety can be raised not
only within the U.S. but also in the rest of the world.
Without augmentation, GPS is already used as a supplemental
means of navigation, in addition to conventional ground-based
navigation. Augmented by the Wide Area Augmentation System (WAAS),
satellite navigation will provide en route, terminal area, and
approach services, down to GLS precision approach. Augmented by
the Ground Based Augmentation System (GBAS), satellite navigation
will serve all categories of precision approach.
A second civil frequency is the next logical step
in modernization of the navigation architecture and providing
improved satellite navigation services. Within the U.S., it will
improve the reliability of satellite navigation, particularly
against the potential threats of interference and ionosphere.
Outside of the U.S., it will make precision approaches possible
with even less infrastructure than is achievable with WAAS alone.
In addition, additional operational benefits will be defined as
the service is defined and applications for that service are developed.
How does WAAS and GBAS fit into the FAA's future NAS architecture?
A. When the final WAAS architecture
is in place, users in the NAS will be able to use GPS/WAAS as
a stand-alone navigation aid for en route through GLS precision
approach operations. Like WAAS, GBAS relies on GPS for basic navigation
signals. GBAS will operate independently from WAAS, while at the
same time complementing WAAS by providing additional GPS augmentation
to support airport requirements for CAT-II/III precision approach
operations. GBAS will also provide a GLS capability at locations
where WAAS cannot, as well as provide a signal, which could be
used, for surface navigation in the terminal area.
What is the difference between an IFR and VFR GPS receiver?
The main difference is that Visual
Flight Rules (VFR) receivers do not have a FAA-approved method
for detecting satellite failures. Instrument Flight Rules (IFR)
receivers have a feature known as Receiver Autonomous Integrity
Monitoring (RAIM) which can detect bad satellite signals and remove
them from the position calculations. IFR receivers usually cost
more than VFR receivers due to this advanced capability.
Why do I have to get FAA approval to install my VFR-only GPS?
Even in VFR conditions, some GPS
receivers can produce hazardously misleading information. The
approval process ensures that the receiver in question will detect
such problems and prevent a user from believing they are somewhere
they are not.
How much does it cost to equip an aircraft with GPS for use in the
National Airspace System (NAS)?
A. The cost to equip an aircraft
with a GPS TSO C129A receiver varies depending on the type of
the receiver, the degree of difficulty of the installation, the
sophistication of the aircraft and existing avionics, and the
level of services desired. Also, the cost of equipping will vary
depending on whether GPS is used as a stand-alone system or as
part of a Flight Management System (FMS).
Most dealers provide a package price when they
sell a receiver. This package includes installation and airworthiness
inspection, as well as the actual equipment. These packages can
range anywhere from approximately $3,000 (US) for a basic general
aviation IFR GPS receiver installation/certification, to $10,000
(US) for a more sophisticated GPS receiver installation/certification
on a commercial aircraft. When comparing prices of GPS avionics
versus existing ground-based avionics, one must consider that
one GPS receiver will eventually replace all avionics associated
with these other ground navigation aids (VOR/DME, NDB, Category
What is the role of current ground-based navigation aids (ILS, VOR/DME,
NDB, LORAN, etc.) in the future successful implementation of GPS
A. The NAS currently
provides several systems to support enroute and terminal area
navigation, including non-precision approach. These include VOR
with associated DME, TACAN, NDB, Loran-C, and GPS.
The operational benefits of GPS/WAAS, especially
increased routing flexibility and many more precision approaches,
will motivate most operators of aircraft used extensively for
IFR operations to equip with GPS/WAAS in the five to six year
period following the availability of services. At that point,
the current ground based systems - VOR, DME, and ILS - will become
back-up systems for these operators. Since most aircraft will
be navigating using GPS/WAAS, substantial reductions can then
be made in the number of VOR/DME and ILS ground facilities. Maintaining
the current VOR/DME system is expensive, thus, there is a considerable
financial incentive to reduce the number of VOR/DME. As soon as
GPS/WAAS avionics are available, operators are anticipated to
begin equipping with it to achieve the associated operational
benefits and convenience.
Are certified GPS avionics available?
Certified GPS receivers have been
available since 1993 for use of the basic GPS system. The FAA
is working with industry and user groups through the RTCA to insure
that WAAS and GBAS avionics are being developed that are both
cost effective and user friendly.