Asiana flight crash at San Francisco

[Bob Zuruncle]

180 to 5

phil gollin

[QUOTE]There is a majority (but not universal) feeling that the ATC advisory "180 kts to 5nm"/4-degree approach was a possible contributory factor./QUOTE]

I'm not sure where you get the 4-degree approach thing from..... that wasn't in the instructions they were given and wouldn't be a normal thing anyway.

But I believe the 180 to 5 miles instruction might have contributed to an unstable approach, but it was not insurmountable. Ms. Hersman indicated that the speed limit for a 777 to select full flap was 160 kts. If you comply with the 180 till 5 instruction then you are accepting that you will not be in the landing configuration until quite late. In other words, you fly to 5 miles at 180 kts, then slow to below 160, then select full flap, then slow to target speed (in this case 137 kts). Only then, with the engines spooled up, and maintaining a stable target speed, on a stable glidepath to the touchdown zone with a rate of descent less than 1000fpm, can you consider the approach to be stabilized....my words are approximate, each company's SOPs will be very specific, but they are all similar.

But different companies specify differences in WHEN this must be achieved by. Some have a blanket "stabilized by 1000 ft" for ALL approaches, some say "by 1000ft in IMC, and by 500 ft in VMC." I don't know what Asiana's rules are, no doubt it will come out in the investigation.

Here are some standard references that pretty much ANY commercial pilot will know and rely on..... if you are on the desired 3-degree nominal glidepath, at 5 miles you will be passing 1500 ft, you pass 1000ft just outside 3 miles, and 500ft at just under 2 miles.

So, to comply with 180 to 5 and be stable by 1000ft in this case would require losing 43kts while continuing a steady descent and configuring in the middle of it, all in less than 2 miles and less than a minute (180 kts is 3 miles a minute). This would require some pretty aggressive handling by someone very familiar with his plane, not someone still trying to get a feel for his new plane. Stable by 500ft would be a lot more do-able but still a challenge for a new-on-type pilot. In any case, some of the plots I've seen, if accurate, show that at 5 miles they were faster than 180kts and higher than 1500ft so it may have been nigh on impossible to be be stable at either gate. The question will be, why did the flying pilot elect to continue, and why did the instructor allow it to continue?

As many have said, saying "unable" might have helped although if they were already too high and too fast it wouldn't have made any difference and this is all moot anyway.

In the past when given a "180 kts to 5 miles" instruction I have said, "Unable, but I can give you 180 to 7 miles and 160 to 5," or similar and the controller has accepted that, but that might not be quite so easy for a non-fluent English speaker to do.

[QUOTE]I am sure that ATC did not impose this as a whim, in fact a couple of people have indicated that it is a common call for noise abatement reasons.
Well, where does that policy come from ?
Is it an airport operating requirement ? Is it just something that they would prefer ?/QUOTE]

It's not noise abatement. It's because there is following traffic that is catching you up. If they get too close, they will have to go around adding one extra plane to an already busy arrival pattern. This is probably not intuitive to non-pilots, but on approach the planes behind you are always catching you up. Why?..... because you always get the the point where you have to slow down before they get to their point where they have to slow down. Why doesn't ATC slow them all down at the same time?... Sounds like it might work, but it doesn't. You end up with a massively long conga line of planes flying slowly, wasting gas, and causing more delays. It's ATC's job to try and manage the problem efficiently, sometimes it doesn't quite work out for all sorts of reasons, hence the requests to keep the speed up. But ATC doesn't know the particulars of your plane's limitations and capabilities, that's the pilot's job and it's up to him to say "unable" when it's just not practical.