FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 12. Aircraft Avionics Systems | 3. Ground Operational Checks for Avionics Equipment (Non-Electrical) | 12-37. Compass Check Swing
AC 43.13-1B CHG 1
9/27/01
compass. Once aligned on the heading, the
person in the cockpit runs the engine(s) to ap
proximately 1,700 rpm to duplicate the air
craft’s magnetic field and then the person reads
the compass.
NOTE: (1) For conventional gear air-
craft, the mechanic will have to posi-
tion the magnetic compass in the
straight and level position or mount
the tail of the aircraft on a moveable
dolly to simulate a straight and level
cruise configuration. (2) Remember
the hairline sight compass is only in-
tended to be used as a general piece of
test equipment.
(2) If the aircraft compass is not in
alignment with the magnetic North of the
master compass, correct the error by making
small adjustments to the North-South brass
adjustment screw with a nonmetallic screw
driver (made out of brass stock, or stainless
steel welding rod). Adjust the N-S compen
sator screw until the compass reads North (0°).
Turn the aircraft until it is aligned with the
East-West, pointing East. Adjust the E-W
compensator screw until it reads 90°. Con
tinue by turning the aircraft South 180° and
adjust the N-S screw to remove one-half of the
South’s heading error. This will throw the
North off, but the total North-South should be
divided equally between the two headings.
Turn the aircraft until it is heading West 270°,
and adjust the E-W screw on the compensator
to remove one-half of the West error. This
should divide equally the total E-W error. The
engine(s) should be running.
pass reading every 30°. There should be not
more than a plus or minus 10° difference be
tween any of the compass’ heading and the
magnetic heading of the aircraft.
(4) If the compass cannot be adjusted to
meet the requirements, install another one.
NOTE: A common error that affects
the compass’ accuracy is the mounting
of a compass or instruments on or in
the instrument panel using steel ma-
chine screws/nuts rather than brass
hardware, magnetized control yoke,
structural tubing, and improperly
routed electrical wiring, which can
cause unreasonable compass error.
(5) If the aircraft has an electrical sys
tem, two complete compass checks should be
performed, one with minimum electrical
equipment operating and the other with all
electrical accessories on (e.g. radios, naviga
tion, radar, and lights). If the compass read
ings are not identical, the mechanic should
make up two separate compass correction
cards, one with all the equipment on and one
with the equipment off.
(6) When the compass is satisfactorily
swung, fill out the calibration card properly
and put it in the holder in full view for the pi
lot’s reference.
d. Standby (wet) Compass. Adjustment
and compensation of the Standby Compass
may also be accomplished by using the “com
pass swing” method.
(3) With the aircraft heading West, start
your calibration card here and record the mag
netic heading of 270° and the compass reading
with the avionics/electrical systems on then
off. Turn the aircraft to align with each of the
lines on the compass rose and record the com
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