Procedure -Cont. - P-340

T-34C INSTRUMENTS

CHAPTER SIX

needle 15 below the 90 benchmark to return the aircraft back to the arc.

Approaching the arc, lead the turn onto the arc and resume Arcing Procedures.

If DME is greater than desired, you are outside the arc. To correct, turn to

ii.

place the head of the TACAN needle 15 above the 90 benchmark.

Once established on the arc in a nowind situation, remain on the arc by altering

aircraft heading and/or bank angle to maintain the head of the TACAN needle on or

near the 90 benchmark. Strive to stay within .2 DME.

NOTE

When altering aircraft heading, consider the position of the head of

the TACAN needle relative to the 90 benchmark. In a nowind

situation:

Head of the needle on the 90 benchmark

DME constant

Head of the needle below the 90 benchmark

DME increases

Head of the needle above the 90 benchmark

DME decreases

When arcing, crosswinds may cause the aircraft to drift off of the arc.

If drifting off the arc, Turn to place the head of the needle above or below

the 90 benchmark, as required. A correction of 10 to 30 degrees will normally

suffice. Once reestablished on the arc, continue Arcing Procedures, but

maintain a drift correction, just as you do when tracking a radial. If the drift

correction is insufficient, repeat the procedure and apply a more appropriate

drift correction.

NOTE

The rate of deviation from, or correction to, an arc will vary with

the size of the arc, distance from the NAVAID, TAS, wind

direction, and velocity.

EXAMPLE: Figure 635 illustrates a typical arcing situation. The aircraft is inbound

to the TACAN station at 150 knots groundspeed, flying a course of 90 (inbound on the

270 radial). You are instructed to arc north at 10 NM.

At Point "a" the aircraft is at the leadpoint. Start the turn to intercept the arc

ii.

now.

iii.

At Point "b" you have just intercepted the arc. The head of the TACAN needle

is on the 90 benchmark and the DME is showing 10.

RADIO INSTRUMENT FLIGHT PROCEDURES 6-59