Compass Swing Requirements

by JM
(Singapore)

What FAR requires a compass swing?


ANSWER: The compass calibration requirements for small aircraft (less than 12,500 lbs maximum take-off weight) can be found in FAR’s 23.1327 and 23.1547.

The compass calibration requirements for large aircraft (more than 12,500 lbs maximum take-off weight) can be found in FAR’s 25.1327 and 25.1547.

They are both similar in wording with the exception that a large aircraft cannot have more than 10 degrees variation.

FAR’s 27 and 29 have the same requirements for small and large helicopters.


Does it apply to all airplane regardless of size and weight?

ANSWER: Yes, it is required for both small and large aircraft. I have pasted the sections of FAR’s 23 and 25 below for your reference:

I have also included a link below to download an excerpt from AC 43.13-1B which provides further information about compass swings:

AC 43.13-1B, Section 3, Ground Operational Checks


FAR 23.1327

Magnetic direction indicator.

(a) Except as provided in paragraph (b) of this section--

(1) Each magnetic direction indicator must be installed so that its accuracy is not excessively affected by the airplane's vibration or magnetic fields; and

(2) The compensated installation may not have a deviation, in level flight, greater than ten degrees on any heading.

(b) A magnetic nonstabilized direction indicator may deviate more than ten degrees due to the operation of electrically powered systems such as electrically heated windshields if either a magnetic stabilized direction indicator, which does not have a deviation in level flight greater than ten degrees on any heading, or a gyroscopic direction indicator, is installed. Deviations of a magnetic nonstabilized direction indicator of more than 10 degrees must be placarded in accordance with Sec. 23.1547(e).

Amdt. 23-20 Eff. 09/01/77


FAR 23.1547
Magnetic direction indicator.

(a) A placard meeting the requirements of this section must be installed on or near the magnetic direction indicator.

(b) The placard must show the calibration of the instrument in level flight with the engines operating.

(c) The placard must state whether the calibration was made with radio receivers on or off.

(d) Each calibration reading must be in terms of magnetic headings in not more than 30° increments.

(e) If a magnetic nonstabilized direction indicator can have a deviation of more than 10 degrees caused by the operation of electrical equipment, the placard must state which electrical loads, or combination of loads, would cause a deviation of more than 10 degrees when turned on.]

Amdt. 23-20, Eff. 09/01/77

FAR 25.1327
Magnetic direction indicator.

(a) Each magnetic direction indicator must be installed so that its accuracy is not excessively affected by the airplane's vibration or magnetic fields.

(b) The compensated installation may not have a deviation, in level flight, greater than 10 degrees on any heading.

FAR 25.1547

Magnetic direction indicator.

(a) A placard meeting the requirements of this section must be installed on, or near, the magnetic direction indicator.

(b) The placard must show the calibration of the instrument in level flight with the engines operating.

(c) The placard must state whether the calibration was made with radio receivers on or off.

(d) Each calibration reading must be in terms of magnetic heading in not more than 45 degree increments.

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