Turnpoint Analysis

CHAPTER FIVE

T-6A NAVIGATION

Example

The aircraft is currently on a course of 180 and on a base airspeed of 180 KIAS. The last

turnpoint placed the aircraft 1/2 NM right of track and 8 seconds late (10+20 planned, 10+28

actual). Total wind was determined to be 120/15 compensations are 4 left crab (compensated

heading 176 for 10 knot crosswind), and a compensated airspeed of 185 (base airspeed 180 with

5 knots of headwind compensation). A standard course correction was performed. No time

corrections were done because mission remained with +12 sec of preflight.

2 Minute Prior Call. The subsequent leg is course 180 (same as current leg). Therefore at the

2 minute prior call outbound heading was given as 176 and airspeed remains at 185 knots

(Remember total wind is thought to be 120/15). Altitude and turnpoint description/hazards

are given as well.

The next turnpoint shows the aircraft 1 NM left of course. The point is abeam at 18+20;

preflight was 17+50, updated to a time of 17+58. Therefore the mark-on-top call is "Heading

176, Time is 18 + 20, Airspeed remains 185, Clear turn." From this information, the aircraft is

30 seconds off of preflight and is an additional 22 seconds late after about 8 minutes of flight.

Wings Level Call

Heading, airspeed, altitude, and fuel are a reiteration of the 2 min prior call and a cross-check

against what the aircraft is actually doing. In this case, the plane should be heading 176, airspeed

of 185 knots, and altitude correspondent with leg requirements. Fuel is read from the gauges and

mission is recommended to "continue" (situation dependent).

Turnpoint Analysis. We were 1 NM left of course and since there was no heading change, the

geometry of the turn leaves us at 1 NM off. A course correction should now be initiated. 20 Rt

for one minute is one acceptable correction. Therefore "Turn right heading 196, time in 19 + 00

time out 20 + 00."

Time Analysis. Aircraft is 30 seconds off preflight timing so a correction must be initiated.

That correction is to "Increase compensated airspeed (of 185 knots) by 20 knots to 205 knots.

Time in 19 + 30, time out 24 + 30." Total correction of 5 + 00 was calculated because 6 seconds

are made up for every minute of increased speed, (10% of 180 knots is ~20 knots, and 10% of

1 min is 6 sec). Therefore to make up 30 sec, divide by 6 and add a zero to the remainder. (i.e.,

30 6 = 5 so 5 + 00 is the result).

Update ETA to the next point should remain at preflight as long as the speed correction is out

prior to the point.

Wind Consideration. Wind is as preflighted IF error can be attributed to something else.

However, for the purpose of discussion let us calculate what the wind magnitude and direction is

and how it will affect us in the future.

5-32

FLIGHT PROCEDURES