BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

AFMAN 11-217V1 3 JANUARY 2005 121
determined when the bearing pointer passes 90 degrees to the inbound course.
7.6.2. TACAN. Station passage is determined when the range indicator stops
decreasing.
7.6.3. ADF. Station passage is determined when the bearing pointer passes 90° to the
inbound course.
7.6.3.1. NOTE: When established in an NDB holding pattern, subsequent station
passage may be determined by using the first definite move by the bearing pointer
through 45° index on the RMI.
7.7. Time and Distance Check. To compute time and distance from a station, first turn the
aircraft to place the bearing pointer on the nearest 90° index. Note the time and maintain
heading. When the bearing pointer has moved 10°, note the elapsed time in seconds and
apply the following formulas to determine time and distance:
7.7.1. Divide the elapsed time in seconds by the degrees of bearing change to obtain
minutes from the station: 120 divided by 10 = 12 minutes from the station.
7.7.2. Multiply your groundspeed in nautical miles per minute by the minutes from the
station.
7.7.2.1. NOTE: The accuracy of time and distance checks is governed by the existing
wind, the degree of bearing change, and the accuracy of timing. The number of
variables involved causes the result to be an approximation. However, by flying an
accurate heading and checking the time and bearing closely, you can get a reasonable
estimate of time and distance from the station.
7.8. Groundspeed Check. Groundspeed checks are done to aid in calculating ETAs to
fixes, which are useful for position reports, fuel computations and other mission timing
problems.
7.8.1. Conditions. A groundspeed check can be made while maintaining a course to or
from a TACAN/VORTAC station. As a guide, however, groundspeed checks should be
performed only when the aircraft slant range distance is more than the aircraft altitude
divided by 1,000. For example, if the aircraft is at FL 200, groundspeed checks should be
performed when beyond 20 nautical miles. Checks made below 5,000 feet are accurate at
any distance.
7.8.2. Begin Timing. To perform the groundspeed check, begin timing when the range
indicator shows a whole number. After the predetermined time has elapsed, check the
range indicator and note the distance flown. Apply the following formula to determine
groundspeed: Multiply the distance flown times 60 and then divide the product by the
elapsed time in minutes. For example, if you fly 12 NM in 2 minutes, then your
groundspeed is 360 knots. ((12 NM x 60)/2 min = 360 knots)
7.8.2.1. NOTE: For precise computation, time for longer periods and solve the
problems on a computer. To simplify computations, use a 2-minute time check and
multiply the distance traveled by 30, a 3-minute time check, distance times 20; or a 6-
minute time check, distance times 10. A rapid groundspeed check can be
accomplished by timing the range indicator for 36 seconds and multiplying the
distance traveled by 100.