*4E Airplane Systems - Magnetic Compass

Question 0

1. How does the magnetic compass work?

FAA-H-8083-25

Answer 0

Magnetized needles fastened to a float assembly, around which is mounted a compass card, align themselves parallel to the earth’s lines of magnetic force. The float assembly is housed in a bowl filled with acid-free white kerosene.

Question 1

2. What limitations does the magnetic compass have?

FAA-H-8083-15

Answer 1

The jewel-and-pivot type mounting allows the float freedom to rotate and tilt up to approximately 18° angle of bank. At steeper bank angles, the compass indications are erratic and unpredictable.

Question 2

3. What are the various compass errors?

FAA-H-8083-15

Answer 2

Oscillation error—Erratic movement of the compass card caused by turbulence or rough control technique.
Deviation error—Due to electrical and magnetic disturbances in the aircraft.
Variation error—Angular difference between true and magnetic north; reference isogonic lines of variation.
Dip errors:
Acceleration error—On east or west headings, while accelerating, the magnetic compass shows a turn to the north, and when decelerating, it shows a turn to the south.
Remember: ANDS
A ccelerate
N orth
D ecelerate
S outh
Northerly turning error—The compass leads in the south half of a turn, and lags in the north half of a turn.
Remember: UNOS
U ndershoot
N orth
O vershoot
S outh