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Comment by firesteelrain | Hacker News Reader

I get that but in DC airspace near Reagan?

Yes, you're right, lousy airspace design. Flown perfectly the chopper should have been no closer than 75' from the airplane if everyone is flying exactly on altitude (which never happens, you have to give at least +/-50'). Couple that with the difficulty of picking out an airplane against the hundreds of backlights of the valley and disaster was inevitable.

The FAA says that I can't fly closer than 500 ft to a shed in the desert, but a Blackhawk is fine to be within 75 ft of a part 121 airliner in a bravo.

Yeah but the Blackhawk requested visual separation. It shouldn't have, it couldn't tell the difference between the CRJ and any number of lights around it. Anyway, at that point the request was granted and you see how it ended.

I recall the tower establishing that they could maintain visual separation, not a request being made from the helicopter. My point is that if everything had gone perfectly, as little as 75 ft of separation would be provided. This is unacceptable in this context for reasons should have been clear ahead of time, but very unfortunately are made clearer in hindsight.

Let's refresh recollections. TFA: "Shortly after the Black Hawk passed over Washington’s most famous array of cherry trees, an air traffic controller at nearby Ronald Reagan National Airport alerted the crew to a regional passenger jet in its vicinity. The crew acknowledged seeing traffic nearby. One of the pilots then asked for permission to employ a practice called “visual separation.” [...] "Visual separation approved,” the controller replied."

There's no ambiguity here.

This doesn't really address my point, but the ambiguity arises from the fact that there are often implicit understandings tunneled through standard phraseology that may or may not be intended. We don't know exactly what the Blackhawk crew said. Clearly tower thought they'd be staying clear of the CRJ, but the Blackhawk crew (to some degree) thought they'd be staying clear of some other lights in the area.

Regardless, 91.119 applies (harshly, and unambiguously, in some cases) to significantly safer operations than 75 ft visual separation from passenger aircraft in bravo airspace. That is absurd. Failure was built into the design from the beginning.

What is your point, that 75' isn't enough separation? Of course it's not enough. But you know as well as I do that visual separation is normal, encouraged even. We know pretty clearly what the Blackhawk crew said. They said they had the traffic in sight and requested visual separation from the reported traffic, not from some passive lights on the ground.

Yes indeed, failure was built in to the airspace design.

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