T-39 FLIGHT PREPARATION
d. Course control
Theoretically, you should always roll out on the radial after leading turns; however, this
is not always the case. As soon as the aircraft position can be determined after a turn, a
correction should be made to the proper radial.
Prior to any course change a wind-adjusted heading should be determined in order to
maintain course on the next leg. Knowledge of the winds (either preflight or computed)
allows a quick determination of crab; only minor heading adjustments should be needed for
the leg. If the winds are unknown, observe the drift after having been on course, then
return to course and adjust the heading to compensate for the drift. The CDI can be a very
effective tool in managing drift.
Any CDI needle deflection indicates you are off course. Remember the needle is a "fly
to" indication and deflects in the direction you must turn. A good rule of thumb is to turn
10º from wind corrected heading for every mile you are off course.
NOTE: The TACAN is the primary NAVAID enroute.
e. Estimated Time of Arrival
The ETA to the next point is given during the two-minute prior call. To determine
ETA to the next point, divide the leg distance by ground speed in miles per minute and add
to the ETA of the upcoming point.
NOTE: on a 90 o turn the crosswind component becomes headwind component.
1. 420 kts ground speed, leg distance 84 NM.
2. 84 NM / 7 NM per minute = 12 minutes.
After the initial estimate you may set up "gates" to further refine the time. A gate is a
distance equal to a whole number of minutes based on the current ground speed. A six-
minute gate would be 39.0 NM, given a 390 kts (6.5 NM/min) ground speed. Note that a
six-minute gate is the ground speed in knots divided by 10 (since six minutes is a tenth of
an hour), and a five-minute gate is the ground speed in miles per minute multiplied by 10
then divided by 2.
NOTE: Use Aircraft clock (time mode) for ETAs vice the flight time or elapsed time modes.
f. Estimated IAF fuels
Estimated fuel at the Initial Approach Fix (IAF) is given during the wings-level call and
after each ground speed check. Several techniques for fuel computation may be used. Four
will be explained in the following discussion and are summarized in Figure 2-1. The
following examples use the information below:
DISTANCE AND ETE1
Adjusted for preflight winds