From earlier posts:
(posted 8 Aug)
Monday TSB Briefing
Again caveat phone quality.
Height above Threshold 50-100'
Threshold a/s 146 kt; gs 164kt
a/s at touchdown 148kt.
(posted 18 Aug)
FROM : AIRBUS CUSTOMER SERVICES TOULOUSE TX530526F
The short final and landing were performed manually with the autopilot (AP) and autothrust (ATHR) disconnected at about 300 feet AGL. The aircraft was in configuration FULL with auto-brake selected to MED.
There was a right variable crosswind of about 20 kts and a tail wind component during the final stage of the approach.
At the time of touchdown, the airspeed was 143 kts and the ground speed 148 kts. Visibility was reported to be 0.5 to 0.25NM in heavy rain.
The touchdown zone is located approximately 4000 feet from the threshold of the 9000-foot runway.
There is one point that I have not yet seen mentioned. I do not want to "speculate", and will confine myself to using the TSB and Airbus quotes above and will (bravely) assume the figures they give as facts.
1. Over threshold, IAS roughly correct,
but an 18Kt tailwind.
2. Touchdown - IAS of same (correct I assume) magnitude, but now only a
5K tailwind.
3. Poor vis due heavy rain => (significantly) contaminated runway.
Nobody seems to mention the effect of the
decreasing tailwind... It is the same as an
increasing headwind. Effectively, from the threshold, the aircraft had to "lose" about another 15K of IAS... whilst at a groundspeed of ~160K. For the few posters here who have flown real aircraft, and particularly Airbuses (I have flown A340s and A32x series) will know that Airbuses are "slippery", quite happy to add a few knots here and there (GS Mini, not a precise ATHR), and have a damn good wing, which all => float. Until you get the thing on the ground, the deceleration is poor, especially in ground effect.
Of course, having got the thing on the ground, with a contaminated runway, deceleration will still be poor... and from the posts / TSB (?) / Airbus, it seems that once landed everything went as expected.
Like all accidents, I suspect there will be a number of factors that all added up. No doubt the performance manual said it was OK to land on this Runway, Wet, at this weight. But to what tailwind? A wild guess that the A340 (like A320) is limited to 10K tailwind in the calcs. Very difficult for a crew, flying in poor conditions, to notice the gust veering in the latter approach stages to exceed the 10K (?) figure. Probably still OK,
until the tailwind now unfairly disappears (!) in the flare / float, and this will
not be factored into the Perf Manual calcs. And again, the immediate Perf Manual will probably have allowed for Wet, but not "Flooded" runway...
Go-Around in flare / after touchdown. Not really trained for... I have done one for real (ABZ), but it is purely a personal instinctive decision by one or other of the Flt Crew. Whilst with 20:20 hindsight, and maybe the Inquiry will confirm, the GA option seems a good one; I reckon a Sim exercise with this scenario (unbriefed) would see the majority doing what happened here...
Lessons: well, some obvious immediate ones for those who do fly, and take advantage of this unfortunate crew. The real / precise lessons will come out in due course from the TSB.