this post was submitted on 23 Nov 2023
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The GPS chips have internal limits on how fast they think they can move. If they determine that they are moving faster than 300m/s they will stop outputting any results for a period of time. This limit is, IIRC, put in at the silicon level, so only military chips can bypass it.
If you try to use mapping apps on a plane you sometimes run into this issue.
It is trivial to make your GPS receiver firmware ignore these limits. There are even open-source receivers (SwiftNav piksi, for example). Modifying a binary is much harder, but not impossible for a motivated state like Iran or Russia. It's best to think of the COCOM limits as suggestions.
But even the fastest airliners at the moment (A330 neo) moves slower than 300m/s. Wikipedia claims that COCOM limits are even higher so I don't think that they are the reason for the inaccurate tracking on planes.
There's also a height limit
Turns out it's 1000 knots (~600m/s), or 18,000 feet. So it's the altitude in this case. But a slow-moving drone at <18,000ft is fine.
Maybe a misapplication then. I've run into it with model rocketry before (for good reason)
Oh, neat. I was not aware of that. I have seen that before but thought it was due to the phone not being able to lock on to the signal from inside a big metal tube.