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Comment by Animats | Hacker News Reader

This was a very close call. Initial reports indicated it was like an ordinary go-around. No. "The incident pilots advanced the thrust levers when the airplane was about 85 feet above ground level. Flight data recorder data indicate the airplane was over the taxiway at this time. About 2.5 seconds after advancing the thrust levers, the minimum altitude recorded on the FDR was 59 feet above ground level."

They overflew an Airbus A340 on the taxiway, tail height 55 feet.

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Mercury News did a good visualization of how close the AC flight came to contact:

http://www.mercurynews.com/2017/07/18/watch-exclusive-animat...

I'm utterly amazed at how calm the other pilots sounded as they watched the AC plane fly towards them.

Indeed. I'm curious what options the pilot of UA1 (the 787 sitting at the end of the taxiway) had. There literally was no time to move the plane anywhere else.

Watch the first few seconds of this video:

https://www.youtube.com/watch?v=MnzNvhQxu90

The pilots should not have mistaken the taxiway for the runway. There simply are too many differentiating features between the runway and the taxiway.

This isn't acceptable piloting.

Both pilots have said they thought the lit runway was 28L, and thus the taxiway, without visible approach lights, was 28R. If the pilots thought the approach lights for the desired runway were obscured by ground fog, which is possible at SFO, they might have made that assumption.

Wait for the NTSB report. This one will be closely analyzed for years.

Something is deeply wrong somewhere if ground fog can make an airplane land on a taxiway. Either airport design, or pilot training, etc... But this should not be an understandable mistake.

Something doesn't add up then, the listed elevation for SFO is 13.1 ft MSL. http://www.airnav.com/airport/KSFO

UPDATE: tolerances around GL are 20 ft https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&SID=&r=PART&n=...

"...the minimum altitude recorded on the FDR was 59 feet above ground level." [emphasis added]

AGL (elevation above ground level), not MSL (elevation above mean sea level). The runway/taxiway elevation is already taken into account. They were 59 feet above the taxiway.

Also, they might not have been directly above the A340 at lowest altitude.

They were very close. See [1]. They were over the centerline of taxiway C, and 85 feet AGL crossing taxiway W. Minimum altitude was 2.5 secs later. There were three planes ahead, an A-340, a B-787 (also 55 feet high at the tail), and some UAL jet of about the same size.

A few feet lower and there would have been a collision.

[1] https://ntsb.gov/investigations/Pages/DCA17IA148.aspx

Wow. A few feet lower, and they might have clipped a tail. I wonder what would have happened.

My point, by the way, was that tails are relatively speaking, breakaway structures. So maybe not much would have happened.

I've had three accidents where my vehicle was hit from the side by another, moving at ~100 km/h. In two of them, the other vehicle hit crumple zone stuff, and I hardly felt the impact. In the third, there was frame-frame contact, and I experienced extreme angular acceleration. It almost ripped my head off.

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