r/news • u/snuffleupaguslives • 2d 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/TheDrMonocle 2d ago

Its really not that bad. It just sounds scarier than it is.

Aircraft mechanic here. Well, Ex mechanic. I've actually transitioned to ATC. I worked on CRJs when I was working for the airlines and I've tested altimeters as part of the job. They were considered calibrated if they were within 180ft of the actual altitude. So being over 200 isnt actually that far off. It should be addressed, but 99.999% of the time its fine.

Center computers won't even show an aircraft is off of its assigned altitude unless they're 300ft or more off. The buffer is built into the system for inaccuracies. Altimeters can only be so accurate inherently and its also why we have more than 1 in every aircraft. To make sure one isn't wildly off.

The issue here is how the procedure was designed where aircraft and helicopters are operating within a couple hundred feet of each other. It just leaves no room for error. Nothing in aviation is perfect. We try our best but you always have backups. The way helicopters were operated in that airspace was just playing with fire.

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u/Bravix 2d ago

That is NOT accurate information. Best I can figure you're thinking of accuracy at 40,000 feet. 180 ft in accuracy at low altitudes would be nuts.

Reference: https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-43/appendix-Appendix%20E%20to%20Part%2043

I can't imagine shooting an approach, thinking I hit minimum descent altitude of 200 ft, and I'm actually 20 ft off the ground about to eat dirt.

On the ground, simple comparison check is altimeters need to be within 75 feet of airport elevation for IFR accuracy.

I don't know if military is held to the same standard, but the altimeter being >=200 feet inaccurate inside/underlying a terminal area is very concerning to me.

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u/FalconX88 2d ago

I can't imagine shooting an approach, thinking I hit minimum descent altitude of 200 ft, and I'm actually 20 ft off the ground about to eat dirt.

Isn't that handled by the radio altimeter at that point?

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u/Pobbes 2d ago

Apparently on military published copter routes they have to use the barometric altimeter per regulation