It is not very hard to implement the subj. with a ring (maybe even 4-6 would be enough) of photodiodes mounted on the top of a copter.
Position of the sun can be calculated from GPS data and time. It could even work in moonlit nights too.

This would probably not work in the noon in tropics, or under really heavy cloudiness, but in 99% of real situations it would greatly reduce the chances of crash when magnetic compass went nuts - no matter the reason.

It is not very hard to implement the subj. with a ring (maybe even 4-6 would be enough) of photodiodes mounted on the top of a copter.
Position of the sun can be calculated from GPS data and time. It could even work in moonlit nights too.

This would probably not work in the noon in tropics, or under really heavy cloudiness, but in 99% of real situations it would greatly reduce the chances of crash when magnetic compass went nuts - no matter the reason.