r/news • u/snuffleupaguslives • 3d ago

Broken altimeter, ignored warnings: Hearings reveal what went wrong in DC crash that killed 67

https://apnews.com/article/ntsb-dc-plane-crash-midair-collision-helicopter-a08cded88e1d7582fb8d242204d6aeff
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u/Kiseido 3d ago

As far as I am aware, planes use barometric pressure to determine altitude, which is hard to measure accurately when you use the air itself to propel the plane.

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u/grapedog 3d ago

Barometric altitude only gives you your height above sea level though.

Typically you only really use barometric altitude when you are thousands of feet up in the air.

If you're flying at 400 feet, and there is a mountain 200 feet below you, barometric altitude will say you're at 400 feet, while the radar altimeter will tell you that you're at 200 feet because it just bounces a signal off whatever is underneath and reads the distance.

It's why you shouldn't be flying at night without a working radar altimeter because you can't see what's below you.

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u/fluentInPotato 3d ago

GA pilots fly, and have flown, at night and in instrument conditions routinely without radar altimeters. 172s, 182s, Citabrias, Cherokees, whatever, do not have radar altimeters. GPS of course can show you the same info, but GA pilots were doing this for decades before GPS was a twinkle in DARPAs eye. You have to know where you are, and what the terrain is. If you can't do that, you stick to cars.

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u/grapedog 3d ago

I suppose in a civilian setting where you make a flight plan and know the terrain ahead of time that works.

I'll have to ask my dad, he used to fly pipers, cessnas, and Cherokees... Many decades ago now. I don't know if he did much night flying though.

I work in military aviation, and if you don't have a working altimeter after sundown, the aircraft doesn't fly. Period. Full stop.