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AIM 

6/17/21 

RWY 24.” Some GPS procedures have a Terminal 
Arrival Area (TAA) with an underlining RNAV 
approach. 

(c) 

For flight planning purposes, 

TSO-C129() and TSO-C196()

equipped users 

(GPS users) whose navigation systems have fault 
detection and exclusion (FDE) capability, who 
perform a preflight RAIM prediction for the 
approach integrity at the airport where the RNAV 
(GPS) approach will be flown, and have proper 
knowledge and any required training and/or 
approval to conduct a GPS-based IAP, may file 
based on a GPS

based IAP at either the destination 

or the alternate airport, but not at both locations. At 
the alternate airport, pilots may plan for: 

(1) 

Lateral navigation (LNAV) or circling 

minimum descent altitude (MDA); 

(2) 

LNAV/vertical navigation (LNAV/ 

VNAV) DA, if equipped with and using approved 
barometric vertical navigation (baro-VNAV) equip-
ment; 

(3) 

RNP 0.3 DA on an RNAV (RNP) IAP, 

if they are specifically authorized users using 
approved baro-VNAV equipment and the pilot has 
verified required navigation performance (RNP) 
availability through an approved prediction program. 

(d) 

If the above conditions cannot be met, any 

required alternate airport must have an approved 
instrument approach procedure other than GPS

 

based that is anticipated to be operational and 
available at the estimated time of arrival, and which 
the aircraft is equipped to fly. 

(e)  Procedures for Accomplishing GPS 

Approaches 

(1) 

An RNAV (GPS) procedure may be 

associated with a Terminal Arrival Area (TAA). The 
basic design of the RNAV procedure is the “T” design 
or a modification of the “T” (See Paragraph 5-4-5d, 
Terminal Arrival Area (TAA), for complete informa-
tion). 

(2) 

Pilots cleared by ATC for an RNAV 

(GPS) approach should fly the full approach from an 
Initial Approach Waypoint (IAWP) or feeder fix. 
Randomly joining an approach at an intermediate fix 
does not assure terrain clearance. 

(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 informa-
tion 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, request-
ing or accepting vectors which will cause the aircraft 

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Navigation Aids