If it’s a smaller plane (such as a CRJ / ERJ) with only one IRU, it will not be able to determine if GPS is valid or not, so the drift correction gets spoiled.
Large commercial aircraft are using 3 IRUs, with newer aircraft using ADIRUs. If GPS does not agree with the three IRUs, the GPS data is thrown out. If the GPS is within tolerance, correction is applied. You could build up very small errors over a long distance, but you should still be pretty close to the airfield when you get there.
assembly@lemmy.world 1 year ago
Yeah I have the same question. Based upon a comment above, it looks like the independent gyro system is updated for drift based upon the spoofed GPS data and thus causes issues. If the IRS is not updated at all then drift becomes a bigger issue but if it’s updated regularly with valid GPS data then it’s a good thing. So the challenge is to only update the gyro drift with valid GPS data which I am guessing is hard to determine.
Dimand@lemmy.world 1 year ago
Pretty much this, look up Kalman filters if you want details. The most likely explanation is that they are tuned to effectively trust GPS more than the internal IMU for long periods of time. Really good IMUs are very expensive and still drift but have high speed output. When it works well, GPS is cheap and doesn’t drift but with a slow update rate. The cost optimisation probably means that the IMU data is usually only trusted for a few seconds, probably 10 min at most before it takes whatever the GPS says as truth. If they lost gps signal through jamming, then they would keep navigation on the less certain IMU data, but the GPS sensor thinks all is well so they shift position.
There is probably a software upgrade to the filter that could be used to limit these attacks, but I imagine it’s an active area or research.