aim-98

AIM

11/3/22

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) Receiver Autonomous Integrity Moni-

toring (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)

Civilian pilots may obtain GPS RAIM

availability information for nonprecision approach
procedures by using a manufacturer

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supplied RAIM

prediction tool, or using the Service Availability
Prediction Tool (SAPT) on the FAA en route and
terminal RAIM prediction website. 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

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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.

(3)

The military provides airfield specific

GPS RAIM NOTAMs for nonprecision approach
procedures at military airfields. The RAIM outages
are issued as M

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series NOTAMs and may be

obtained for up to 24 hours from the time of request.

(4)

Receiver manufacturers and/or data-

base 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.

(5)

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.

(6)

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.

(7)

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 nor 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 FAF.

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Navigation Aids