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AIM

10/12/17

1

−1−24

Navigation Aids

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 procedures
in the navigation database). Flying point to point on
the approach does not assure compliance with the
published approach procedure. The proper RAIM
sensitivity will not be available and the CDI
sensitivity  will not automatically change to ±0.3
NM.  Manually setting CDI sensitivity does not
automatically change the RAIM sensitivity on some
receivers. Some existing non

−precision approach

procedures cannot be coded for use with GPS and will
not be available as overlays.

(9)

Pilots should pay particular attention

to the exact operation of their GPS receivers for
performing holding patterns and in the case of
overlay approaches, operations such as procedure
turns. These procedures may require manual
intervention by the pilot to stop the sequencing of
waypoints by the receiver and to resume automatic
GPS navigation sequencing once the maneuver is
complete. The same waypoint may appear in the route
of flight more than once consecutively (for example,
IAWP, FAWP, MAHWP on a procedure turn). Care
must be exercised to ensure that the receiver is
sequenced to the appropriate waypoint for the
segment of the procedure being flown, especially if
one or more fly

−overs are skipped (for example,

FAWP rather than IAWP 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.

(10)

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.

(11)

A fix on an overlay approach identi-

fied 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.

(12)

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.

(13)

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

(1)

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.

(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) GPS NOTAMs/Aeronautical Informa-

tion

(1)

GPS satellite outages are issued as

GPS NOTAMs both domestically and internation-
ally. 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.