3/21/24 

AIM 

(3) 

When an approach has been loaded in the navigation system, GPS receivers will give an “arm” 

annunciation 30 NM straight line distance from the airport/heliport reference point. Pilots should arm the 

approach mode at this time if not already armed (some receivers arm automatically).  Without arming, the 

receiver will not change from en route CDI and RAIM sensitivity of 

±

5 NM either side of centerline to 

±

1 NM 

terminal sensitivity.  Where the IAWP is inside this 30 mile point, a CDI sensitivity change will occur once the 

approach mode is armed and the aircraft is inside 30 NM.  Where the IAWP is beyond 30 NM from the 

airport/heliport reference point and the approach is armed, the CDI sensitivity will not change until the aircraft 

is within 30 miles of the airport/heliport reference point.  Feeder route obstacle clearance is predicated on the 

receiver being in terminal (

±

1 NM) CDI sensitivity and RAIM within 30 NM of the  airport/heliport reference 

point;  therefore, the receiver should always be armed (if required) not later than the 30 NM annunciation. 

(4) 

The pilot must be aware of what bank angle/turn rate the particular receiver uses to compute turn 

anticipation, and whether wind and airspeed are included in the receiver’s calculations. This information should 

be in the receiver operating manual. Over or under banking the turn onto the final approach course may 

significantly delay getting on course and may result in high descent rates to achieve the next segment altitude. 

(5) 

When within 2 NM of the Final Approach Waypoint (FAWP) with the approach mode armed, the 

approach mode will switch to active, which results in RAIM and CDI changing to approach sensitivity. 

Beginning 2 NM prior to the FAWP, the full scale CDI sensitivity will smoothly change from 

±

1 NM to 

±

0.3 

NM at the FAWP. As sensitivity changes from 

±

1 NM to 

±

0.3 NM approaching the FAWP, with the CDI not 

centered, the corresponding increase in CDI displacement may give the impression that the aircraft is moving 

further away from the intended course even though it is on an acceptable intercept heading. Referencing the 

digital track displacement information (cross track error), if it is available in the approach mode, may help the 

pilot remain position oriented in this situation. Being established on the final approach course prior to the 

beginning of the sensitivity change at 2 NM will help prevent problems in interpreting the CDI display during 

ramp down. Therefore, requesting or accepting vectors which will cause the aircraft to intercept the final 

approach course within 2 NM of the FAWP is not recommended. 

(6) 

When receiving vectors to final, most receiver operating manuals suggest placing the receiver in 

the non

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sequencing mode on the FAWP and manually setting the course.  This provides an extended final 

approach course in cases where the aircraft is vectored onto the final approach course outside of any existing 

segment which is aligned with the runway. Assigned altitudes must be maintained until established on a 

published segment of the approach. Required altitudes at waypoints outside the FAWP or stepdown fixes must 

be considered. Calculating the distance to the FAWP may be required in order to descend at the proper location. 

(7) 

Overriding an automatically selected sensitivity during an approach will cancel the approach mode 

annunciation. If the approach mode is not armed by 2 NM prior to the FAWP, the approach mode will not become 

active at 2 NM prior to the FAWP, and the equipment will flag. In these conditions, the RAIM and CDI sensitivity 

will not ramp down, and the pilot should not descend to MDA, but fly to the MAWP and execute a missed 

approach. The approach active annunciator and/or the receiver should be checked to ensure the approach mode 

is active prior to the FAWP. 

(8) 

Do not attempt to fly an approach unless the procedure in the onboard database is current and 

identified as “GPS” on the approach chart. The navigation database may contain information about 

non

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overlay approach procedures that enhances position orientation generally by providing a map, 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 Supplement 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

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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 

Navigation Aids 

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