GPS Overlay Approaches - P-340

CHAPTER SEVEN

T-34C INSTRUMENTS

when flying along a flight planned routing or along a final approach course where auto-

sequencing of waypoints is required. An example of this is when given radar vectors to the FAF,

select OBS mode on the GPS, select the FAF as the active waypoint, and set the final approach

course in the CDI. Once established on the inbound course and prior to the FAF, reselect LEG

mode on the GPS.

GPS OVERLAY APPROACHES

Overlay approaches consist of GPS waypoints overlayed on conventional (VOR, VOR/DME

etc...) non-precision approaches (i.e., VOR or GPS-A at CEW pg 6-49). Though overlays have

the same minimums as the underlying approach, they offer the opportunity to fly an instrument

approach procedure using GPS. Because GPS approaches are designed as a TO-TO system

(meaning you navigate to one fix, cross it and proceed to the next fix), overlays are not a perfect

fit with the underlying procedure. Some conventional approaches, for example, have no FAFs, so

GPS would not be able to navigate to a fix, nor would it know when to switch the CDI sensitivity.

This problem is solved by inserting synthetic, GPS-specific "sensor final approach fixes" on

approach overlays when required. There are various GPS overlay approach fix naming standards

involving characters and numbers. It is not critical that the student memorize the naming

methods, however, it is important to recognize that the GPS database uses this protocol. Listed

below are examples of GPS overlay fixes the student may see as they scroll through the fix list:

D006J

A DME arc fix, with the "D" meaning DME, 006 the radial and "J" the

distance, 10 miles (J is the 10th letter of the alphabet)

ORW19

Alongtrack fix at DME 19

FF142

FAF on 142 course

MA142

MAF on 142 course

RW14

MAP, runway 14

CF151

Capture or course fix on the 151 radial

If any of the above listed fixes are an actual five-letter named fix, they will have a dash and a

small letter suffix at the end of the waypoint. These suffixes are intended to assist the pilot in

recognizing certain points during the approach, and are visible on the FPL 0, Super NAV 5 and

Super NAV 1 pages. The IAF is denoted by (-i), for example FREBY-i. The FAF is denoted by

(-f), for example ELMOO-f. The MAP is denoted by (-m), for example MA25B-m. The missed

approach holding point is denoted by (-h), for example FITON-h.

WARNINGS

GPS overlay approaches that contain final approach step-

down fixes may not have corresponding waypoints in the

associated GPS approach. It is the pilot's responsibility to

identify these points relative to charted GPS waypoints.

7-28 INSTRUMENT NAVIGATION