NOTE1To 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.
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 situational awareness.
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 require approval.
3. The GPS Approach Overlay Program is an
authorization for pilots to use GPS avionics under
IFR for flying designated nonprecision instrument
approach procedures, except LOC, LDA, and
simplified directional facility (SDF) procedures.
These procedures are now identified by the name of
the procedure and “or GPS” (e.g., VOR/DME or GPS
RWY_15). Other previous types of overlays have
either been converted to this format or replaced with
stand-alone procedures. Only approaches contained
in the current onboard navigation database are
authorized. The navigation database may contain
information about nonoverlay approach procedures
that is intended to be used to enhance 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 Supple-
ment for details on how to identify these approaches
in the navigation database).
NOTE-
Overlay approaches are predicated upon the design
criteria of the ground-based NAVAID used as the basis of
the approach. As such, they do not adhere to the design
criteria described in paragraph 5-4-5k, Area Navigation
(RNAV) Instrument Approach Charts, for stand-alone
GPS approaches.
4. GPS IFR approach operations can be
conducted as soon as proper avionics systems are
installed and the following requirements are met:
(a) The authorization to use GPS to fly
instrument approaches is limited to U.S. airspace.
(b) The use of GPS in any other airspace must
be expressly authorized by the FAA Administrator.
(c) GPS instrument approach operations
outside the U.S. must be authorized by the
appropriate sovereign authority.
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1-1-31
Navigation Aids
f. Equipment and Database Requirements
1. Authorization to fly approaches under IFR
using GPS avionics systems requires that:
(a) A pilot use GPS avionics with TSO-
C129, or equivalent, authorization in class A1, B1,
B3, C1, or C3; and
(b) All approach procedures to be flown must
be retrievable from the current airborne navigation
database supplied by the TSO-C129 equipment
manufacturer or other FAA approved source.
(c) 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 in-flight steps:
(1) Preflight:
Determine the date of database
issuance, and verify that the date/time of proposed
use is before the expiration date/time.
Verify that the database provider has
not published a notice limiting the use of the specific
waypoint or procedure.
(2) Inflight:
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 charts.
Determine that the waypoints are
generally logical in location, in the correct order, and
that their orientation to each other is as found on the
procedure chart, both laterally and vertically.
NOTE-
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.
If the cursory check of procedure
logic or individual waypoint location, specified in
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.
g. GPS Approach Procedures
As the production of stand-alone GPS approaches
has progressed, many of the original overlay
approaches have been replaced with stand-alone
procedures specifically designed for use by GPS
systems. The title of the remaining GPS overlay
procedures has been revised on the approach chart to
“or GPS” (e.g., VOR or GPS RWY 24). Therefore, all
the approaches that can be used by GPS now contain
“GPS” in the title (e.g., “VOR or GPS RWY 24,”
“GPS RWY 24,” or “RNAV (GPS) RWY 24”).
During these GPS approaches, underlying groundbased NAVAIDs are not required to be operational
and associated aircraft avionics need not be installed,
operational, turned on or monitored (monitoring of
the underlying approach is suggested when equip-
ment is available and functional). Existing overlay
approaches may be requested using the GPS title,
such as “GPS RWY 24” for the VOR or GPS
RWY_24.
NOTE-
Any required alternate airport 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.
h. 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 term UNRELIABLE is used in conjunc-
tion with GPS NOTAMs. The term UNRELIABLE
is an advisory to pilots indicating the expected level
of service may not be available. GPS operation may
be NOTAMed UNRELIABLE due to testing or
anomalies. Air Traffic Control will advise pilots
requesting a GPS or RNAV (GPS) approach of GPS
UNRELIABLE for:
(a) NOTAMs not contained in the ATIS
broadcast.
(b) Pilot reports of GPS anomalies received
within the preceding 15 minutes.
3. Civilian pilots may obtain GPS RAIM
availability information for nonprecision approach
procedures by specifically requesting GPS
AIM 2/14/08
1-1-32 Navigation Aids
aeronautical information from an Automated Flight
Service Station during preflight briefings. GPS
RAIM aeronautical information can be obtained for
a period of 3 hours (ETA hour and 1 hour before to 1
hour after the ETA hour) or a 24 hour time frame at
a particular airport. FAA briefers will provide RAIM
information for a period of 1 hour before to 1 hour
after the ETA, unless a specific time frame 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 nonprecision approach proce-
dures 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.
5. Receiver 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 electronic
database.
i. Receiver Autonomous Integrity Monitoring
(RAIM)
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, another type of
navigation and approach system must be used,
another destination selected, or the trip delayed 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 early indications 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 may no longer provide the required
accuracy. The receiver performs a RAIM prediction
by 2 NM prior to the FAWP to ensure that RAIM is
available at the FAWP as a condition for entering the
approach mode. The pilot should ensure that 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 completing the approach.
4. If the receiver does not sequence into the
approach mode or a RAIM failure/status annunci-
ation occurs prior to the FAWP, the pilot should not
descend to Minimum Descent Altitude (MDA), but
should proceed to the missed approach way-
point_(MAWP) via the FAWP, perform a missed
approach, and contact ATC as soon as practical. Refer
to the receiver operating manual for specific
indications and instructions associated with loss of
RAIM prior to the FAF.
5. If a RAIM failure occurs after the FAWP, the
receiver is allowed to continue operating without an
annunciation for up to 5 minutes to allow completion
of the approach (see receiver operating manual). If
the RAIM flag/status annunciation appears after
the FAWP, the missed approach should be
executed immediately.
j. Waypoints
1. GPS approaches make use of both fly-over
and fly-by waypoints. Fly-by waypoints are used
when an aircraft should begin a turn to the next course
prior to reaching the waypoint separating the two
route segments. This is known as turn anticipation
and is compensated for in the airspace and terrain
clearances. Approach waypoints, except for the
MAWP and the missed approach holding waypoint
(MAHWP), are normally fly-by waypoints. Flyover waypoints are used when the aircraft must fly
over the point prior to starting a turn. New approach
charts depict fly-over waypoints as a circled
waypoint symbol. Overlay approach charts and some
early stand alone GPS approach charts may not
reflect this convention.
2. Since GPS receivers are basically “To-To”
navigators, they must always be navigating to a
defined point. On overlay approaches, if no
pronounceable five-character name is published for
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1-1-33
Navigation Aids
an approach waypoint or fix, it was given a database
identifier consisting of letters and numbers. These
points will appear in the list of waypoints in the
approach procedure database, but may not appear on
the approach chart. A point used for the purpose of
defining the navigation track for an airborne
computer system (i.e., GPS or FMS) is called a
Computer Navigation Fix (CNF). CNFs include
unnamed DME fixes, beginning and ending points of
DME arcs and sensor final approach fixes (FAFs) on
some GPS overlay approaches. To aid in the approach
chart/database correlation process, the FAA has
begun a program to assign five-letter names to CNFs
and to chart CNFs on various National Oceanic
Service aeronautical products. These CNFs are not to
be used for any air traffic control (ATC) application,
such as holding for which the fix has not already been
assessed. CNFs will be charted to distinguish them
from conventional reporting points, fixes, intersec-
tions, and waypoints. The CNF name will be enclosed
in parenthesis, e.g., (MABEE), and the name will be
placed next to the CNF it defines. If the CNF is not at
an existing point defined by means such as crossing
radials or radial/DME, the point will be indicated by
an “X.” The CNF name will not be used in filing a
flight plan or in aircraft/ATC communications. Use
current phraseology, e.g., facility name, radial,
distance, to describe these fixes.
3. Unnamed waypoints in the database will be
uniquely identified for each airport but may be
repeated for another airport (e.g., RW36 will be used
at each airport with a runway 36 but will be at the
same location for all approaches at a given airport).
4. The runway threshold waypoint, which is
normally the MAWP, may have a five letter identifier
(e.g., SNEEZ) or be coded as RW## (e.g., RW36,
RW36L). Those thresholds which are coded as five
letter identifiers are being changed to the RW##
designation. This may cause the approach chart and
database to differ 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. MAWPs not located at the threshold will
have a five letter identifier.
k. Position Orientation
As with most RNAV systems, 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. On overlay
approaches, the pilot may have to compute the
along-track distance to stepdown fixes and other
points due to the receiver showing along-track
distance to the next waypoint rather than DME to the
VOR or ILS ground station.
l. Conventional Versus GPS Navigation Data
There may be slight differences between the course
information portrayed on navigational charts and a
GPS navigation display when flying authorized GPS
instrument procedures or along an airway. All
magnetic tracks defined by any conventional
navigation aids are determined by the application of
the station magnetic variation. In contrast, GPS
RNAV systems may use an algorithm, which applies
the local magnetic variation and may produce small
differences in the displayed course. However, both
methods of navigation should produce the same
desired ground track when using approved, IFR
navigation system. Should significant differences
between the approach chart and the GPS avionics'
application of the navigation database arise, the
published approach chart, supplemented by
NOTAMs, holds precedence.
Due to the GPS avionics' computation of great circle
courses, and the variations in magnetic variation, the
bearing to the next waypoint and the course from the
last waypoint (if available) may not be exactly 180_
apart when long distances are involved. Variations in
distances will occur since GPS distance-to-waypoint
values are along-track distances (ATD) 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 the NAVAID.
AIM 2/14/08
1-1-34 Navigation Aids
m. Departures and Instrument Departure
Procedures (DPs)
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_ob-
stacle clearance surface (OCS), which is double the
fixed-wing OCS, and turning areas are based on this
speed as well.
n. Flying GPS Approaches
1. Determining which area of the TAA the
aircraft will enter when flying a “T” with a TAA must
be accomplished using the bearing and distance to the
IF(IAF). This is most critical when entering the TAA
in the vicinity of the extended runway centerline and
determining whether you will be entering the right or
left base area. Once inside the TAA, all sectors and
stepdowns are based on the bearing and distance to
the IAF for that area, which the aircraft should be
proceeding direct to at that time, unless on vectors.
(See FIG 5-4-3 and FIG 5-4-4.)
2. Pilots should fly the full approach from an
Initial Approach Waypoint (IAWP) or feeder fix
unless specifically cleared otherwise. Randomly
joining an approach at an intermediate fix does not
assure terrain clearance.
3. When an approach has been loaded in the
flight plan, 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 it has not already been
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, CDI sensitivity will not change until the
aircraft is within 30 miles of the airport/heliport
reference point even if the approach is armed earlier.
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 informa-
tion 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 altitude.
5. When within 2 NM of the FAWP with the
approach mode armed, the approach mode will
switch to active, which results in RAIM changing to
approach sensitivity and a change in CDI 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.
