Direct Routing - P-8210073

RADIO INSTRUMENTS

CHAPTER THREE

course is the reciprocal of the radial. To track on a radial, turn in the shortest direction and place

the head of the number two needle (inbound) or the tail of the number two needle (outbound)

under the heading index. Set the desired course in the course selector window of the course

indicator. Periodically check for drift due to wind, which will be indicated by the number two

needle moving away from the desired radial and by deflection of the CDI from the center.

If off course fly an intercept heading to get back on course (intercept headings are generally

more than 20 degrees, and drift correction headings are generally less than 20). When back on

course, turn to an estimated drift correction heading (Figure 3-1). If this estimated drift

correction heading is excessive, the aircraft will fly off course into the wind. If that is the case,

turn to a heading the same as the course, and allow the wind to drift the aircraft back on course,

then establish a drift correction angle half of the first. If the initial drift correction heading is

insufficient, the aircraft will drift off course downwind. In this case, turn to again intercept the

course, and then establish a new estimated drift correction heading with a greater drift correction

angle than the first. This process is "bracketing". When the correct drift correction angle is

found, the difference between the heading and the desired course will be the "drift correction

angle" ("crab angle"). Drift correction angles may be estimated. Note that the higher the TAS,

the shallower the drift correction angle required to maintain a desired track: the correction

necessary to maintain course at 300 KTAS is about 2 degrees for each 10 knots of direct

crosswind, at 200 KTAS 3 per 10 knots, at 360 KTAS, 1-1/2, etc.

Direct Routing

The definition of "Direct" in the Pilot/Controller Glossary (an appendix in the Aeronautical

Information Manual, the Air Traffic Control Handbook, etc.), is helpful in understanding the

correct procedure for flying a route which includes a "direct" leg:

Direct Straight line flight between two navigational aids, fixes, points, or any combination

thereof.

Cleared direct to:

ATC will occasionally clear an aircraft from their current location direct to a navigational aid.

For example, "Rocket 205, you are cleared from present position direct to the Semmes TACAN."

To proceed directly to a TACAN:

Tune and identify the station.

Turn in the shortest direction to the head of the number 2 needle.

3. Note heading and set this course in the course selector window of the course indicator.

To avoid reverse sensing in the CDI, confirm a "TO" indication in the TO-FROM indicator.

Track inbound on the radial.

RADIO INSTRUMENTS

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