Arcing - P-8210076

CHAPTER THREE

RADIO INSTRUMENTS

Proceed southeast on J24:

Maintain the outbound radial (124).

2. Tune and Identify. One to two minutes prior to the intersection or fix, tune and identify the

new station (ROD, Channel 122).

3. Set the new course in the course selector window of the course indicator (055). Note the

appropriate indication in the TO-FROM indicator (TO).

4. Lead the turn. Lead the turn into the intersection to adhere as closely as possible to the

airway being flown.

Intercept and track the new radial.

ARCING

During TACAN arcing, the aircraft heading should be controlled so that the TACAN needle will

remain on or near the 90 benchmark, and the DME at the desired range. The number and extent

of heading changes will vary with distance from the station and wind conditions. As a general

rule, if the aircraft is allowed to drift inside or outside the arc, a correction of about 5 of heading

per 1/2NM error should be applied (for example, if the aircraft is 1 NM outside of the arc the

nose of the aircraft should be pointed 10 degrees toward the station, (i.e. head of the TACAN

needle should be 10 ahead of the 90 benchmark). In Radio Instrument events in the 2F101, the

student will provide headings to navigate throughout each arc. In the T-2C, once established on

an arc, the IP may be asked to "maintain the arc".

GROUNDSPEED CHECK

A Groundspeed Check can be conducted while maintaining a course, which is oriented generally

to or from a TACAN Station. However, for best accuracy, Groundspeed Checks should be

performed only when tracking on a radial and the DME exceeds the aircraft altitude above the

TACAN divided by 1000. For example, if the aircraft is at FL210 over a TACAN, which is at an

elevation of 1000 MSL, groundspeed checks should be performed when beyond 20 DME.

"Thirty-six second" groundspeed checks conducted with digital DME can be fairly accurate.

However, at jet speeds, especially using the odometer-style DME in a T-2C, 36-second checks

are of questionable value. A, one minute, check is considered the shortest for acceptable

accuracy. Three and six minute checks are proportionately more accurate. As learned during the

primary and intermediate phases of training, groundspeed will be computed by dividing the

distance flown by the elapsed time in minutes and then multiplying by 60:

GROUNDSPEED = Distance Flown / Elapsed time in minutes

Begin timing. Punch the clock when the range indicator shows a whole number and time for at

least one minute.

3-24

RADIO INSTRUMENTS