4 ms·
To give you a bit of insight, around the same timeframe (late October/early November) I directly observed two high-accuracy RTK GPS receivers reporting high acc
by tonyarkles 11mo ago
To give you a bit of insight, around the same timeframe (late October/early November) I directly observed two high-accuracy RTK GPS receivers reporting high accuracy (2cm), full 3D DGPS lock with carrier phase, and positions wandering within about a 5m circle horizontally. The altitude was staying pretty consistent (within about 1m, which was outside of the reported accuracy but not bad) until there was a sudden 60m altitude shift. This was all while they were sitting static on the ground, verified both by the crew and the accelerometer, gyro, and RADAR data.
There wasn’t a software fix per se, but we were able to quickly add a check to verify that the Kalman Filter’s position variance estimate was on the same order of magnitude as the accuracy level that the receivers were reporting and put a big red warning up. This wasn’t a flight-critical system, but it is the first time we’d ever seen that behaviour from those receivers and we’ve used them for 5 years.
- RossBencina 11mo agoNot my area at all, but I'm extremely surprised that a fly-by-wire system would use GPS as an altitude reference. Is that really the case?
- adhambadr 11mo agoIt’s a combined signal system, using pressure based sensors + gps.
- ape4 11mo agoAnd inertial guidance too?
- adhambadr 11mo agoI don’t know what airbus uses I only looked into the schematics of commercial avionics like Garmin. I doubted though IMU drift and calibration introduce more error than they can provide in useful signal, old school pressure sensors + gps adjusted manually or automatically for regional pressure settings (pilots get these numbers through radio when they enter a new pressure area) is accurate enough (~1m). I’ll let a real avionics engineer correct me here, I’d be curious if that signal is worth the hassle + I can imagine such tiny SMD sensors ARE the biggest victims of radiation hallucination.
- a-dub 11mo agoi would expect a huge shift like that to violate the gaussian assumption of the kalman filter? (which i guess is what you're checking, sort of?). regardless i would expect the kalman filter to smooth the shift over some substantial time at least?
- londons_explore 11mo agoI think it more likely these receivers fell for a spoof GPS signal or some software bug internal to the receiver than a solar bitflip.
- tonyarkles 11mo agoIn our case I don’t believe it was solar bitflips but rather wildly changing ionospheric conditions. I was primarily pointing out how you can have a software-only fix for problems like this. Without going too far into the weeds, the fact that the receivers in question were reporting high accuracy under uncertainty is definitely a software bug in the receivers from my perspective. There was a different receiver with a completely different chipset in it on-site too that was experiencing similar issues but was reporting low accuracy. Without going into too much detail, I’ve got pretty good reasons to believe it wasn’t spoofing.