Procedure - P-340

CHAPTER SIX

T-34C INSTRUMENTS

Procedure

Continue on the desired radial to the DME that identifies the lead point. When

turning onto an arc from a radial (using a StandardRate Turn), the amount of lead

(in nautical miles) should be 0.5% of the aircraft's groundspeed.

RADIUS OF TURN

When an aircraft commences a turn, it turns about an imaginary

point. The distance from the aircraft to this point is referred to as

radius of turn. Radius of turn is determined by turn rate and

airspeed. In Figure 6-36 (inset), an aircraft has been flying a 90

heading and turns to 360 (or a 90 turn onto an arc). Position "a"

represents the point where the turn was started and position "b" is

the point where 360 is reached. As you can see, some eastward

travel occurred between the start of the turn and rollout. For a 90

turn, this distance equals the radius of turn. For a StandardRate

Turn at 150 knots, this distance is .8 NM and at 120 knots it is .6

NM.

NOTES

.8 NM and .6 NM are actually approximations. The actual

value is .5% of your GROUNDSPEED. In most applications, the

amount of error introduced by using these approximations is

negligible. However, excessive headwinds or tailwinds may require

adjusting the leadpoint to turn onto the arc.

The values of .8 and .6 NM will be less accurate if you are

sloppy rolling into and out of turns or if you fail to maintain a

StandardRate Turn.

For example, if you are inbound to the station at 150 knots and are instructed to arc at 10

DME, you would begin the turn onto the arc at 10.8 DME. If you are outbound from the

station and desire to arc at 10 DME, your lead point would be 9.2 DME.

Determine the direction of turn at the leadpoint.

At the leadpoint, start a turn in the appropriate direction. Continue the turn until the

head of the TACAN needle is on the 90 benchmark.

Check your DME.

If DME is less than desired, you are inside the arc. To correct back to the arc,

simply maintain the heading. If you have flown excessively inside the arc, (.5

DME or more inside the arc), make a turn to place the head of the TACAN

6-58 RADIO INSTRUMENT FLIGHT PROCEDURES