background image

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.