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change accurately and quickly. Six methods are presented in the following paragraphs. These are not the
only accepted methods but are some of the easier methods to use. As with most time corrections, these
methods are based on flight planned GS.
17.13.1. Proportional Method. The proportional method can be used either high or low-level. Begin by
determining the number of seconds early or late. Next, increase or decrease flight planned GS by that
increment (20 seconds = 20 knots). Hold this correction for the following length of time: flight planned
GS/60 minutes (360 knots/60 = 6 minutes).
AFPAM11-216 1 MARCH 2001 353
EXAMPLE: You are 30 seconds late and your flight planned GS is 420 knots. Increase flight planned
GS (420 knots) by 30 knots (450 knots) and hold it for 7 minutes.
17.13.2. Total Time and/or Total Distance. This method is normally used at high-level but also applies
to low-level. Check the distance to your next checkpoint and compare current Zulu time with desired
Zulu time at the next checkpoint. This will give you a time and distance to go. Set up a ratio on the MB-
4 computer by putting the desired time to go over the distance to go and look above the rate index for
the required GS.
EXAMPLE: Current Zulu time is 1100:00 and distance to go is 140 NM. Desired ETA at the next
checkpoint is 1120:00. You must fly 140 NM in 20 minutes or 420 knots GS (140 NM/20 minutes = 420
knots GS/rate index).
17.13.3. Turn Point Method. During mission planning, a correction factor can be calculated for each
low-level leg. This is done by multiplying each low-level leg time by the appropriate coefficient (Figure
17.3). The correction factor calculated for each leg equals the number of seconds gained or lost for each
10 knots of speed change from flight planned GS over the entire leg.
EXAMPLE: Leg time is 7 minutes, 42 seconds. Flight planned GS is 420 knots. Coefficient extracted
from Figure 17.3 is 1.5. Multiply leg time by coefficient factor (7:42 x 1.5) to equal approximate
correction factor of 12. You are 36 seconds late at your last turn point (based on Zulu time). You will
gain 12 seconds over the length of the low-level leg for each 10 knots increase in flight planned GS.
Therefore, an increase in flight planned GS of 30 knots to 450 knots will gain 36 seconds if 450 knots is
held for the entire leg.
Figure 17.3. Coefficient Table.
17.13.4. Six Minutes Out Method. To use this method, determine the distance remaining to a
checkpoint 6 minutes prior to the time required over the turn point. Multiply this distance by 10 to get
required GS to fly to turn point, starting 6 minutes out.
EXAMPLE: Required time at checkpoint is 1413:27. Six minutes before (1407:27) you are 38.5 NM
from the turn point. A GS of 385 knots at 1407:27 will put you at the checkpoint on time.
17.13.5. Ten Percent Method. Determine the amount of time to gain or lose. Adjust your GS to 10
percent above (if late) or below (if early) of the flight-planned GS (10% x 300 knots = 30 knots). The
rule states that holding the 10 percent increase or decrease of flight-planned GS for 10 minutes will gain
354 AFPAM11-216 1 MARCH 2001
or lose 1 minute. This also means that one can gain or lose 6 seconds for every minute the adjustment is
maintained. To apply this method, determine the 10-percent factor during mission planning.
EXAMPLE: In flight, you determine you are 35 seconds late. Your flight-planned GS is 300 knots. You
should increase your GS by 30 knots (to 330 knots) and hold it for 6 minutes. This will make up 36
seconds.
17.13.6. Incremental Method. To determine the increment, you must find your miles per minute (300
knots = 5 miles per minute). Multiply that by 10 to obtain the increment (5 X 10 = 50 knots). Determine
time ahead or behind in seconds. Divide this time by 10 to obtain the number of minutes to hold the
correction. The rule of thumb states that if the increment is held for 1 minute, you will gain or lose 10
seconds.
EXAMPLE: You are 90 seconds late and your flight-planned GS is 300 knots. The increment is 50
knots. Increase flight-planned GS (300 knots) by 50 knots (350 knots) and hold it for 9 minutes.
NOTE: Remember that most methods are based on flight-planned GS. Apply the correction to the flightplanned
GS, not the current GS.
17.14. Summary. The most important phase of the low-level mission is flight planning. If the mission is
planned well and there is good crew coordination, mission success is greatly enhanced. Consequently,
you should (1) know what aids will be available, (2) be familiar with all phases of the particular mission
and study them until a clear mental picture of the flight emerges and finally, (3) maintain good, reliable
in-flight DR procedures. If you do all this, the low-level mission will be greatly simplified. If not, the
　
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