What is the difference between a "compass swing" and a "check swing" procedure?
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2 Answers
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Based upon the terminology I have heard over the years, a compass swing is the alignment of the compass, normally using a compass rose painted on a surface. The compass is adjusted and a deviation card is created for cardinal points on the compass.
A check swing, as I have heard it referred to, is the checking of the compass, and done with the aircraft running, and electrical loads on, similar to a compass swing, but without the adjustment. The deviation card is verified, but there is no intent of adjusting anything. This was typically done before we ferried aircraft over the ocean, where there would be extended dead-reckoning (before GPS and LORAN), and where flights were close to the polar regions, and compass operation needed to be verified prior to the flight.
Not that a compass is worth much near the poles (grin).
My guess is that check swing is merely a slang term, whereas compass swing is well understood and extensively documented.
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$\begingroup$ In the US maintenance by pilots is governed by FAR Part 43 Appendix A, Paragraph (c). Compass swings are not included in the list of preventive maintenance pilots can do, so must be done by a certified A&P. Compass checks involve no maintenance, so are perfectly fine. $\endgroup$– JScarryApr 17, 2019 at 15:40
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$\begingroup$ @JScarry, you are correct. I did a double check. I also found that when I swung the compass the mechanic put an entry in the log, along with a copy of the deviation card I created. So I guess that is mechanic supervised maintenance. Thanks for pointing out. I removed my addendum, which had that error. $\endgroup$– mongoApr 17, 2019 at 19:19
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$\begingroup$ I happened to notice a bunch of logbook entries with the deviations in the books I was reviewing over the weekend. It seems they often did a compass swing after installing new avionics, which makes sense since the magnetic fields generated by the avionics might change. $\endgroup$– JScarryApr 17, 2019 at 20:30
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$\begingroup$ If a HF radio was added, like for oceanic crossing, we would strap the radio in place, and swing the compass. two degrees off makes a big difference crossing the pond. Topping things off, most of the planes did not have working AP. So it was about 28 hours of stick time for some of them. $\endgroup$– mongoApr 18, 2019 at 0:43
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A compass swing involves adjustment by a qualified person. A check swing can be done by anyone to verify the serviceability of the compass without adjustment. Check swing can be done anytime the compass is suspect or, if required for, annual check. if no adjustment is required no certification by a compass qualified person is required.
