Take a GS check

INSTRUMENTS FLIGHT PLANNING

CHAPTER FIVE

In order to accurately revise ETAs and EFRs, the following method is suggested:

Take a GS check.

Sometime after completion of the GS check, "freeze" the following items in your cockpit (done

simultaneously):

DME

Fuel on board

Fuel flow

Actual clock time

Armed with these figures you can accurately revise your ETAs and EFRs.

Here is a practice example:

DME = MAI 272/35

Fuel on board = 670 lbs

Fuel flow = 240 PPH or 4 lbs/Min

GS = 210

Time: 50+00

At 50+00 we are 35 NM from MAI. With a GS of 210 kts, we are at MAI in 10 minutes

(00+00). To calculate EFR at the IAF we add our ETE to MAI (10 min) to our ETE from MAI

to the IAF (16 min) for a total of 26 min remaining to the IAF. Since our fuel flow is 4 PPM, we

burn an additional 105 lbs to the IAF. Our on-board fuel is 670 lbs 105 lbs = 565 lbs EFR at

the IAF.

This example is an oversimplified case of using the freeze technique. In a real world situation,

your numbers are not likely to be as round as these were, so you must learn to work quickly with

these calculations, since you must simultaneously navigate and communicate.

The procedure described above in which preflight ETEs are combined with actual fuel flow to

predict future fuel states is considered the most practical method for such calculations here in the

training environment. It is assumed that your preflight ETEs are accurate.

If your route of flight (Figure 5-4) was from Pensacola through Crestview, Montgomery,

Meridian, New Orleans, Semmes to the Navy Pensacola IAF, you can see that a GS check

obtained between Crestview and Montgomery would not hold true for the rest of the flight. If

your flight is in a relatively straight line, it is correct to apply GS checks to future legs of flight to

recalculate your ETEs. Whenever possible, the latter technique is employed.

IN-FLIGHT FUEL AND TIME ANALYSIS

5-5