Flightradar24's new GPS jamming map

Re:Flightradar24's new GPS jamming map by phire on Wednesday March 20, 2024 @07:12PM (#39773146)

"Do aircraft systems really only use GPS"

I know older long-range planes from the 70s and 80s had excellent inertial navigation systems.

Not quite as good as GPS, but good enough to know the location of the plane within a few nautical miles. The main problem is that inertial navigation systems drifted over time and required constant recalibration from the crew whenever they had a fix from real navigation beacons and errors could be catastrophic (especially when skirting the edge of Soviet airspace).

I've always wondered if modern avionics suites kept the older style inertial navigation systems as a backup to GPS, or if the systems were deleted when everyone switched to GPS.

I think it would be smart for larger planes to have a modern inertial navigation system that constantly recalibrated off GPS, ready to take over in the case of GPS jamming or spoofing.

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Re:Flightradar24's new GPS jamming map by jjwiseman on Wednesday March 20, 2024 @07:26PM (#39773243)

They do that! Unfortunately, they don't always know when they're being spoofed, so oops, your inertial reference system has just been infected by the spoofed location and now both nav systems are hosed.

https://ops.group/blog/gps-spoof-attacks-irs/

https://aerospace.honeywell.com/us/en/about-us/blogs/spoofin...

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Re:Flightradar24's new GPS jamming map by tjoff on Thursday March 21, 2024 @03:20AM (#39775640)

Though shouldn't be that hard to know if you are being spoofed. You probably have a decent idea of how much the IRS drifts and any large deviations from that or unexpected jumps in GPS should be noted and possibly, maybe manually, rolled-back so that the IRS only considers data before that point.

I understand that current civilian aircraft wasn't designed with that in mind though.

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Re:Flightradar24's new GPS jamming map by t0mas88 on Friday March 22, 2024 @04:13AM (#39788421)

Avionics were designed with the opposite assumption. When a high accuracy location source provides a location (GNSS or DME/DME) the position is updated and it's assumed that could mean a significant jump for the INS.

Practically that was what happened all the time before GPS. You would fly for a few hours over the ocean with no ground based reference, having a reasonable but not perfect INS location. Then get close to the coast where a DME/DME fix was done which updated the INS position as a big jump of up to a few miles.

Filtering GPS updates that are too far "off" the INS state would be an almost opposite design to the original assumptions that DME and GNSS are highly accurate.

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Re:Flightradar24's new GPS jamming map by randomcarbloke on Friday March 22, 2024 @12:27PM (#39792256)

some amount of IRS drift should be ~predictable, an anticipated deviation from GPS could be used as a measure of trust for GPS

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Re:Flightradar24's new GPS jamming map by ericd on Friday March 22, 2024 @09:11AM (#39790358)

It seems like there’d be some use for something that correlates what it sees on the ground with known satellite imagery as a check? Especially for anything low-flying.

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Re:Flightradar24's new GPS jamming map by ogurechny on Thursday March 21, 2024 @06:42AM (#39776909)

Based on discussions of some accidents, pilots often ignore inertial navigation systems at which they rarely look today, and sometimes forget to set the known good location before flights (which does not depend on GPS, as airports don't move).

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Re:Flightradar24's new GPS jamming map by t0mas88 on Friday March 22, 2024 @04:21AM (#39788460)

You can look at the INS position (and compare the position from each INS separately), but practically you're always looking at the "FMS position" which is where the flight management computer thinks you are. That takes INS, GNSS/GPS and other nav beacons into account. So it's technically true that pilots don't often look at the specific screen that has the INS position(s) on it, but you are looking at the FMS position which is basically equal to the INS position if GPS is not updating and you receive no ground signals.

Modern aircraft will also set the known position based on the runway you're taking off from. And when airborne they'll pick up a DME/DME fix and update the location. So while it's procedure to set the known starting location at the gate, there are also other sources.

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