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Navigation Aids

if the procedure turn is not flown). The pilot may have to sequence past one or more fly

overs of the same

waypoint in order to start GPS automatic sequencing at the proper place in the sequence of waypoints.


Incorrect inputs into the GPS receiver are especially critical during approaches. In some cases,

an incorrect entry can cause the receiver to leave the approach mode.


A fix on an overlay approach identified by a DME fix will not be in the waypoint sequence on the

GPS receiver unless there is a published name assigned to it. When a name is assigned, the along track distance
(ATD) to the waypoint may be zero rather than the DME stated on the approach chart. The pilot should be alert
for this on any overlay procedure where the original approach used DME.


If a visual descent point (VDP) is published, it will not be included in the sequence of waypoints.

Pilots are expected to use normal piloting techniques for beginning the visual descent, such as ATD.


Unnamed stepdown fixes in the final approach segment may or may not be coded in the waypoint

sequence of the aircraft’s navigation database and must be identified using ATD. Stepdown fixes in the final
approach segment of RNAV (GPS) approaches are being named, in addition to being identified by ATD.
However, GPS avionics may or may not accommodate waypoints between the FAF and MAP. Pilots must know
the capabilities of their GPS equipment and continue to identify stepdown fixes using ATD when necessary.

(f) Missed Approach


A GPS missed approach requires pilot action to sequence the receiver past the MAWP to the

missed approach portion of the procedure. The pilot must be thoroughly familiar with the activation procedure
for the particular GPS receiver installed in 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.


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 Monitoring (RAIM)


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.


Civilian pilots may obtain GPS RAIM availability information for nonprecision approach

procedures by using a manufacturer

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

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.


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.