56-101-01200 Revision G
Page 6
2. SPECIFICATIONS
A.
Physical Data
Size (H, W, L)
3.34 in. (8.5 cm), 2.36 (6 cm), 2.75 in. (7 cm)
Weight
0.72 lbs. (0.325 kg)
Table 1
Physical Characteristics
B.
Scale
The Sight Compass is marked with letters representing the cardinal directions, North (N), East
(E), South (S), and West (W), and a number for each 30 degrees between these letters. For
example, 3 = 30°, 6 = 60°, and 33 = 330°.
There are long and short graduation marks between the letters and numbers, with each long
mark representing 10 degrees and each short mark representing 5 degrees.
C.
Accuracy
Accurate to within ±1 degrees.
3. BACKGROUND INFORMATION
A. A compass swing must be performed whenever any ferrous component of the system (i.e., flux
valve compensator, or Standby Compass) is installed, removed, repaired or a new compass is
installed. Additionally, a compass swing must be performed on the following occasions:
1. When the accuracy of the Compass is suspected.
2. After any cockpit modification or major replacement involving ferrous metals.
3. When the Compass has been subjected to shock from a hard landing or turbulence.
4. After aircraft has passed through a severe electrical storm.
5. After a lightning strike.
6. Whenever a change is made to the electrical system.
7. Whenever a change of cargo is likely to affect the Compass.
8. Whenever an aircraft operation is changed to a new geographic location with a major
change in magnetic deviation.
9. After aircraft has been parked on one heading for over a year.
10. When flux valves are replaced.
B.
Understanding Compass Errors
The error of any compass is the angular difference between true north and compass north. This
angle is the algebraic sum of the deviation and variation. These are two terms commonly used
in connection with compasses that should not be confused.
1. Compass deviation is the difference between the heading of the aircraft, as indicated by the
compass and the actual magnetic heading of the aircraft. The deviation is called plus or
minus (east or west respectively) to indicate how it must be applied to the compass heading
