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Comment by lukecampbell | Hacker News Reader

I've never flown a B777 or any heavy aircraft so I can't comment on their typical flares, but in a Cessna 172 the flare doesn't induce a positive rate of climb, it simply slows the vertical descent speed to something manageable for touch down, a positive vertical speed seems counterintuitive to me as a good flare. What I want to know is what his IAS (indicated air-speed) at the decision altitude.

Again the only thing I've flown are parachutes and some hours in a C172 and a C182.

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It gives a pretty good estimate of the error involved in the descent rate reporting. Probably accurate +/- 200 FPM or so.

The airspeed encoder is probably from the same system that displays the pilot instruments, indicated airspeed IAS. I thought it odd that the analysis of conditions didn't think 125 and 98 were ridiculously low airspeeds, but claimed that an approach around 130 knots was a "fast approach". However what little I know about the 777 from the flightsim and real pilot community is that a typical approach is around 150-something slowing to a bit above 130 at flare. I've read some claims from actual heavy pilots that under really light conditions a Vref below 120 is theoretically possible.

None of us know the weight and balance calcs so its impossible to determine if the pilots were doing the correct thing, although it is possible to determine they were flying a flight path implying they thought they were very light indeed. Now why? Who knows. Maybe because they were right, they were light. Maybe because they were low-ish on fuel. Maybe they didn't trust their IAS instrument. Maybe their IAS was actually broken and comparing their visual approach with instruments, well, its just a really strong headwind today. Maybe they made a math error. Somebody overcontrolled?

He could have found this info by violating the copyright of numerous google-able flight sim forums, and forums with real genuine 777 pilots talking about their experience with the 777. Instead he violates the copyright of a picture which we've all already seen, oh well.

About the speed, you're correct – 130 kts for a 777 is not fast, I was mistaken. In fact the NTSB just said the target approach given by the pilots was to be 137 kts. I should have chose one of the higher airspeeds given but I did not want to give a high estimate. I am not familiar with 777 speeds and should of done some more research in that regard. I did however, write that I found the sub-100 speeds to be extremely slow, even suggesting that it's most likely below stall speed – which seems to be correct as the NTSB says the stick shaker went off some 4 seconds before impact.

I read sometimes you can get a Vref under 120, great density altitude, sea level, winter, no pax cargo and low on fuel, but yeah when the IAS is reporting 98 you're pretty much screwed under any conditions. Maybe it was already on the ground at that point, if it wasn't.. it going to be on the ground real soon...

I would imagine some of the flightsim people I know are flying the approach under identical conditions right now. Would be interesting to hear at what point they found it unrecoverable. 98 kts is unrecoverable, but I wonder when it went unrecoverable. One problem with sims is if you know how its supposed to turn out, that screws up your actual reaction if you sim it 20 times trying different things. All you need is a cockpit distraction to totally screw up an approach. Maybe a false alarm of some type at just the wrong moment.

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