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Comment by piker | Hacker News Reader

Interesting how radiation issues could be solved in software.

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.

Not 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?

It’s a combined signal system, using pressure based sensors + gps.

And inertial guidance too?

I 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.

i 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?

I think it more likely these receivers fell for a spoof GPS signal or some software bug internal to the receiver than a solar bitflip.

In 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.

Perhaps it's improving the checksum algorithm on network packets, or even ... adding one.

Makes you wonder, if/how _passengers_ are directly protected against the radiation

They're not. Excessive high altitude flight increases your chance of developing melanoma.

https://pmc.ncbi.nlm.nih.gov/articles/PMC9447865/

Ok, I'll take an aisle seat more often now instead of a window seat.

Unless you fly as often as pilots and other onboard staff, it's unlikely to be significant.

If flying were invented today, I bet it wouldn't be allowed due to the radiation. It's more than many medical procedures which guidelines say to only do when the medical benefits outweigh the radiation risk.

I suppose if flying were invented today the plane would have no windows and the pilots would use cameras.

Clearly the benefits of flying outweight the radiation risks, though.

Passengers flying now and then, it's not a big deal, but aircrews are at increased risk of cancer.

It comes down to voting algorithms and memory persistence. Sometimes there is a threshold before data are "voted out".

I don't work on the A320 but solar radiation is a well-known issue in avionics, generally speaking.

Edit: deleted some speculation

Finally turning on the ECC RAM option?

About one third require hardware mods.

Maybe there's a range that requires a change?

Now imagine, if it was over the air update, then maybe there would be no disruption?

Agreed, I expected additional shielding or something physical like that.

s/solved/mitigated/

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