Comment by kcg | Hacker News Reader

Comment by kcg | Hacker News Reader

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> Who is saying that procedures allow one plane to take off when one is "3 miles out"

The FAA says that, specifically the 7110.65 which governs ATC rules and procedures. In a radar environment it allows for departures when the arriving aircraft is 2+ miles from the runway, and there will be at least 3 miles of separation within 1 min of takeoff. A separate rule requires that the departing aircraft is at least 6000ft down the runway and airborne before the arrival crosses the runway threshold.

If there is a departing plane rolling up to the hold short line and confirmed ready for immediate takeoff, there is possibly time to get them out and maintain separation. If it's low visibility, the departing plane is rolling slowly and not confirmed ready, then it's a bad bad idea.

I think that's generally correct, but I'm not familiar with all of the rules. That said, even if the Southwest plane had been faster on the runway, they weren't going to be able to maintain 6000 feet of separation. If Southwest starts rolling from a dead stop, and Fedex is barreling in at 140 knots from two miles, they're necessarily going to converge until Southwest accelerates, which takes a minute.

Juan Brown [1] made an interesting point also. For a Cat II or III approach, and this one was definitely Cat III, there is an ILS critical area that Southwest would have impinged on as it was taking off.

The controller very clearly made a huge mistake.

[1]https://www.youtube.com/watch?v=SvUOHa8n7aQ

It says there can be as little as 2 miles of separation which I read as 2 miles when the wheels lift off begining acceleration would end up with 0 ft of separation.

The rules specifically state how 2 miles of separation is defined. 7110.65 5-8-4-Note 1 says "This procedure permits a departing aircraft to be released so long as an arriving aircraft is no closer than 2 miles from the runway at the time. This separation is determined at the time the departing aircraft commences takeoff roll." [1]

Just to keep stating this: I'm not at all defending the AUS controller here. A squeeze play like this in low visibility is needlessly reckless.

[1] https://www.faa.gov/air_traffic/publications/atpubs/atc_html...

2 miles is like 43 seconds at 165. You are right standard seems insufficient.

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