Arcing - P-8710057

T-6A INSTRUMENT NAVIGATION

CHAPTER FOUR

4. Not flying the drift corrected heading to stay on course while switching to the secondary

station.

Not selecting the proper source for the CDI.

Not using a courtesy call prior to giving a position report.

Not leading the turn if required.

411. ARCING

Arcing is defined as flying at a constant distance from a TACAN or VOR/DME station by

reference to DME. Arcing around a station may be required to comply with an ATC clearance

and is an integral part of certain TACAN or VOR/DME approaches and DPs.

TACAN and VOR/DME arcs are used during all phases of flight. An arc may be intercepted at

any angle, but is normally intercepted from a radial. An arc may be intercepted when proceeding

inbound or outbound on a radial. A radial may be intercepted either inbound or outbound from

an arc. The angles of intercept (arc to radial) are approximately 90. Because of these large

intercept angles, the use of accurate lead points during the interception will aid in preventing

excessive under or overshoots (Figure 4-6.)

ARC INTERCEPTION FROM A RADIAL

Tune and identify the station.

Tune the proper frequency.

Identify the station with Morse Code.

Monitor as required.

Confirm the correct source for the bearing pointer and CDI.

Twist the proper course into the CDI.

Determine the direction of turn.

3. Lead Point. Determine a lead point that will result in positioning the aircraft on or near the

arc at the completion of the initial turn. By using turn radius, you can calculate a good lead

point. Turn radius is the distance the aircraft travels around a point when making a 90 standard

rate turn (SRT). To determine the turn radius, take 1/2 of 1% of your GS. For a SRT at 150

KIAS, the turn radius is 0.75 NM (rounded to 0.8). At 120 KIAS, the turn radius is 0.6 NM.

Strong winds may require adjusting the lead point.

INSTRUMENT NAVIGATION

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