Originally Posted by
KayPam
What is the matter at hand with this Sully flare ?
Was the AOA (about 14°) at touchdown inferior to what it should have been (alpha max for CONF 2, whose value I don't know by heart) ??
I think Sully should have been able to get that very last 3.5 degrees (stall margin) of pitch he was asking for (by holding full aft stick).
I have no problem with the concept of alpha-protection mode, yet the execution of it below 100' AGL (radar altimeter) should not have included phugoid-dampening feedback terms, the items to blame here, and is what kept Sully from pitching a tad more in flare.
Keep in mind Sully hit the water at 9.5 degrees pitch, and 11 would have been considered ideal, so he was only off by a little, and that last 2 or 3 degrees of pitch denied him would have lowered his touchdown impact (feet/min vertical speed when hitting).
Originally Posted by
albatross
I thought of that one too this morning. I'd almost forgotten about it. I can remember the old 1988 video of it at the Paris Air Show. That should have been a warning to Airbus to examine what was going on at very very low altitudes (100 feet and below) to allow the pilot to really use every last stall margin possible.
Originally Posted by
misd-agin
He didn't read the airspeed "just fine." He misread it by more than 15-19 kts ("safely above Vls" vs 15-19 kts below Vls) and didn't process that his speed was barely above the red band which is an image we never see in normal approaches. That is what extreme stress will do to you and is understandable. The NTSB reports covers the stress impact on human performance.
OK, agreeing he was too low on airspeed during the descent. I'm a flight control engineer, which makes me conclude I'm just glad he was flying and not stalling! Sure an optimal speed which happens to give max(L/D) at whatever weight they had would be great, giving more pitch room to flare too. Yet, getting airspeed as low as possible is laudable, which he did, and he did have 3.5 degrees of actual stall margin left, so did he really mess it up that bad????
Originally Posted by
misd-agin
Without the AOA protection AB built into the FBW we can only speculate what would have happened without AOA protection. At a high AOA, reached at 150', he then attempted to raise the nose at 100'. That attempt, with only a couple of knots above stall speed, might have lead to a situation where the vertical descent rate would have been even higher at water entry. That's if he realized it and didn't stall the a/c. If he had stalled a non FBW protected a/c the outcome would have been worse.
As I've said, alpha-protection is a good thing above 100 feet, just
not at 100' AGL and below when the phugoid damping feedback was preventing full use of max lift from flare to impact.
Originally Posted by
KayPam
This is very relevant.
I pointed them out in a document that I posted on a french forum.
I could provide a quick translation.
Is anyone interested in looking into my findings ?
I'd look into it, from a flight control engineer's point of view, not a pilot. Although I've flown gliders, and, coincidentally, that time Sully was a glider pilot too...
Can you post an English translation in a pdf file or something?