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“GPS” in the title (e.g., “VOR or GPS RWY 24,”
“GPS RWY 24,” or “RNAV (GPS) RWY 24”).
During these GPS approaches, underlying ground−
based 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 equipment
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.
2/19/04 AIM
Air Navigation Aids 1−1−35
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.
i. 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 conjunction
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 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 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.
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.
j. 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
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