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This symbol is on the tarmac at Ramona, CA airport. I've seen it at other small GA airports from Google Earth but I don't know what it is. Can someone please explain?

Ramona, CA airport

Federico
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PJNoes
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1 Answers1

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That is a Compass Rose, painted on a Compass Calibration Pad. It's used to mark a location on the airport surface that is suitable for calibrating the compass of an aircraft.

Here's one in a slightly different style:
Compass pad photo

and a more basic one from an FAA diagram:
Compass pad diagram

More information on the requirements for the compass rose / compass pad can be found in AC 150/5300-13, in Appendix 6.

voretaq7
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    Fun bonus fact: The compass rose in your photo was painted by The Ninety-Nines - they volunteer to do compass rose paintings at a lot of GA airports, and you can recognize their work by the 99s logo in the center of the compass rose. – voretaq7 Feb 08 '16 at 20:08
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    Related: Marking the way. – mins Feb 08 '16 at 20:16
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    @voretaq7 nice trivia. The 99s logo confused me because the runway is 9-27 and I thought it might be related to the runway heading. – PJNoes Feb 08 '16 at 20:23
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    Magnetic north drifts around fairly significantly - are these repainted on a regular basis? – davidA Feb 09 '16 at 03:36
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    @meowsqueak Per the advisory circular: Magnetic surveys of existing compass calibration pads must be performed at regular intervals of 5 years or less. … Pads not resurveyed after 5 years or after nearby construction should not be used. - Whether this is actually done in practice varies, so it is prudent to check with the airport to determine the last time the compass pad was properly surveyed. – voretaq7 Feb 09 '16 at 05:22
  • @voretaq7 It seems odd that the compass rose is aligned to magnetic north instead of true North. Mag north does have to be re-calibrated which seems like a lot of work if the rose would have to be re-painted. I realize the variation changes slowly but if it was aligned to true north it wouldn't have to be re-calibrated, except maybe every 50,000 years or so. – PJNoes Nov 23 '16 at 16:50
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    @PJNoes Remember we're calibrating a magnetic compass: If the compass rose were aligned to True North they would have to paint or other wise mark (with non-magnetic materials) the magnetic variation with the same level of precision - that means they still have to do the periodic surveys, even without regular repaints. They also need to accurately point the aircraft's nose (and its magnetic compass) at the appropriate angles accounting for that variation, which isn't easy without painted markings - at that point they may as well use a calibrated master sight compass rather than a compass rose. – voretaq7 Nov 24 '16 at 05:41