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Comment by t0mas88 | Hacker News Reader

And this is why it's mandatory to check GPS availability when planning an IFR flight to an airport that only has GPS approach procedures. And it's also required to plan an alternate airport that has a non-GPS approach available.

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That doesn't really have anything to do with the GPS jamming tests. That's because GPS isn't actually global, or at least wasn't a couple decades ago. What you're checking is the number of satellites available on your flight path at the time you'll be there such that you can create an accurate and redundant 3d fix.

You’re talking about RAIM. But you’re also required to check NOTAMs, where these tests are documented, under the “all pertinent information” clause of the preflight regs.

You're required to check both, RAIM availability (unless you have a WAAS type GPS) and also the NOTAMs where these jamming tests are published.

I’m not too worried about commercial airlines. I’m more worried about press-button-and-fly weekend IFR warriors.

I would also be worried about systems like Cirrus’ VisionJet Safe Return, that turn the aircraft into an autonomous vehicle if a passenger activates the system due to an incapacitated pilot, as GPS is required for its automated path planning to autonomously return to an airport and land.

I haven’t investigated, but I would be curious how such a system responds when GPS is degraded or unavailable.

That’s already a rare event though, so the probability of it coinciding with a GPS outage is smaller still. Time integral of risk exposure and all that.

Rare as it is—and I’d argue it’s not as rare as some people think, having experience three avionics GPS loss-of-signal events in the past two years (in different aircraft)—they’d be nuts not to have considered that risk in the design. I can’t find the AFM supplement for Safe Return but to a first approximation, it wouldn’t be out of the question for it to go into a heading and altitude hold until it reaquires.

Surely they also use GLONASS and Galileo.

It's not required to plan an alternate that has a non-GPS approach if you have a WAAS-enabled GPS receiver, which is almost all of them these days. You can file a primary and alternate with only RNAV approaches.

WAAS won’t help you when the GPS signal is being jammed. It’s ground-based navaids, pilotage, or stay home.

That's a non-sequitur. The person I was replying to said you always have to plan at least one airport with a non-GPS approach.

You’re right of course. I was addressing the larger question of the impact of GPS jamming tests on aviation in general. Less of a reply to you and more of a note to anyone else reading.

But you are still required to check GPS availability and these jamming tests are published way in advance.

I don't remember saying you didn't... Of course you still have to check RAIM availability, but you don't have to plan an alternate with a different approach type.

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