Flight Procedures

Instrument Flight

Adjustments to the position of the head of the bearing pointer relative to the 90 degree benchmark will

have to be made to compensate for the position of the wind relative to the aircraft on the aircraft as it

moves around the arc.

When intercepting a radial from an arc, you must determine which way you have to turn to intercept and

fly the radial in the correct direction (Figure 24). Since you will most often be performing an arc as part of

an approach or departure procedure, you can obtain this information from the appropriate approach plate

or SID. To turn from an arc to a radial, your main consideration is to determine the proper lead in radials.

Radials diverge as you get further from a station and are 1 nm apart at 60 DME. Take this divergence into

account when calculating your lead point for the turn. To calculate the lead point for intercepting a radial

from an arc, first you must calculate or estimate the ground speed. Then apply the following formula:

Divide the arc DME into 60 then multiply the quotient by 1 percent of the ground speed.

For example, if you are on a 15 DME arc at 250 knots ground speed, your lead point will be 10 radials

(60 divided by 15 equals 4, 1 percent of 250 is 2.5, and 2.5 multiplied by 4 equals 10).

When making your intercept turn, you can also use the movement of the bearing pointer and CDI as a

guide to determine when to initiate the turn. When you are flying close to the station, the CDI will move

too quickly to follow at 30 degrees AOB. Therefore, the turn must be initiated at the calculated lead point.

To intercept a radial from an

arc, first set the desired

course in the course select

window. Next, determine

your lead and then turn

R270

using a 1/2 SRT when you

reach the lead point.

Finally, vary your AOB in

R264

the turn with the movement

of the CDI so that it is

R258

centered when the turn is

complete. Do not exceed

10 DME ARC

30 degrees AOB.

R252

18 Radial Lead

The above formula assumes

300 KGS

a 90 degree turn. However,

1/2 SRT

inbound radial intercepts will

60 X 1% GS = Lead Radial

require a greater lead than

DME

outbound because the

aircraft turns through more

than 90 degrees.

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(12-00) Original

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