56-101-01200 Revision G
Page 9
CHAPTER 3: OPERATION
WARNING:
Before performing the procedures indicated in this chapter, remove all personal items
which might contain ferrous material, such as keys, pocketknives, watches, cell phones,
radios, pocket calculators, metal pens and pencils, etc. Beware of metal frame eyeglasses,
sunshades, metal shirt or jacket buttons, and steel belt buckles. All these items may be
magnetic, thus affecting the functioning of the Sight Compass.
1. ESTABLISHING A PERMANENT REFERENCE POINT
When the Sight Compass is first received, it is suggested that a permanent reference check point
be established. If, at any time, there is reason to suspect the readings obtained during the Aircraft
Compass testing, the Sight Compass can be rechecked using these reference points. To determine
one or more appropriate reference procedures:
A. Select an unobstructed view of at least 100 feet away from any buildings, machinery, fences,
power lines, etc. which could affect the magnetic environment. Beware of concrete runways with
embedded steel mesh or of any underground cables or pipelines. Also, the area selected should
be where future construction is unlikely. Battery Installation and Verification.
B. From the selected area, locate a prominent object at least 1 mile distant from the sighting
location. Again, try to anticipate an area where future construction is unlikely.
C. Remove all magnetic personal items that could affect the Compass. Clear the designated
location of any magnetic sources, induced electromagnetic field, or source of ferromagnetic
materials that could affect the Earth’s magnetic field. These items may include, but are not
limited to tools, cellphones, watches, jewelry and metal pens. These items must be removed
from the test set area, at least 5 feet away, to avoid adversely affecting the Compass reading.
Articles that must be worn, such as eyeglasses, should be checked and demagnetized
accordingly.
D. Carefully align the Compass sight on the chosen distant object or objects. Note and record the
Sight Compass readings.
E. Mark the observation point with some non-ferrous item for future reference.
F. Make a permanent record of the observation point, the referenced distant object or objects and
the Sight Compass readings.
2. TESTING SIGHT SUITABILITY
Before attempting to check and calibrate an Aircraft Compass, the area to be used should be
tested. It is recommended that the area be as far as possible from any magnetic disturbance.
Suggested distances are 50 feet from the aircraft being swung and 100 feet from any buildings,
large items of machinery, power lines, fences, etc. However, the area could appear to meet all of
these requirements but be unusable because of the steel mesh in the ramp or underground cables
or pipelines. To ascertain if the chosen area is satisfactory, proceed as follows:
A. Ensure that the area is at least 100 feet in diameter or adequate to accommodate the
dimensions of the aircraft being tested.
