T-6A INSTRUMENT NAVIGATION
1. Only one approach may be entered into FPL 0. Non-
precision approaches are automatically deleted from the FPL 0
page (active flight plan) in non-volatile memory 5 minutes after the
GPS is turned off. Desired approaches must be loaded again to be
2. There are non-precision approaches which are not suited to
the GPS operational characteristics and which are not included in
the database. Verify the database contains desired approaches for
desired airports prior to flight.
GENERAL PROCEDURE FOR GPS NON-PRECISION APPROACHES
In order to conduct an approach, one must be loaded into the active flight plan. Approaches can
only be entered in FPL 0, the active flight plan, and must be loaded prior to the FAF. As the
aircraft flies towards the airfield, the "approach arm" mode is activated automatically at 30 NM.
At that time, the CDI scale factor smoothly changes from the enroute mode of + 5.0 NM (not
degrees) to the terminal mode of + 1.0 NM over a 30-second transition period. If the GPS APR
switch is pressed when the aircraft is more than 30 NM from the airport, the approach arm mode
is activated but the CDI scale remains + 5 NM until the aircraft is within 30 NM of the airport.
When the approach arm mode is activated, the GPS will cue the pilot to press ALT to update the
The most significant point to understand when using the GPS for non precision approaches is the
use of the OBS mode. When the GPS is in OBS mode, rotating the OBS knob will rotate the
course select line on the GPS, but will not change course select line when in LEG mode. When
given radar vectors to the FAF, select OBS mode on the GPS, select the FAF as the active
waypoint, and set the FAC in the CDI. This will display the FAC through the FAF so you can
intercept it when being vectored to final. Once established on the inbound course and prior to
the FAF, reselect LEG mode on the GPS. This will provide the automatic waypoint sequencing
required for the approach mode to activate.
The "approach active" mode can only be activated by the GPS itself and occurs automatically
when they aircraft is approximately 2 NM from the FAF with an approach loaded into the active
flight plan. At this point, the GPS indicators will change colors from blue to green.
The pilot must select LEG mode.
Adequate integrity monitoring must be available to complete the approach.
RAIM must be available at the FAF and MAP.
8-8 GLOBAL POSITIONING SYSTEM