Friday, July 03, 2009

Aviation Update

AF 447

Stories early in the week noted the clock was about wind down on the black box pingers, meaning Air France might never be able to find the devices, which would seriously degrade the ability of investigators to solve the case.

Yet without this key information French investigators have evidently seen enough forensic evidence to change their minds about how the plane impacted the water:
French crash investigators said Thursday they have determined that an Air France jetliner that plunged from a stormy sky on June 1 was intact when it smacked belly-first into the Atlantic Ocean at high speed
It's not clear whether they think the aircraft was in a flat spin or simply descending in flight profile but not flying. The comment about no life jackets being found inflated might be inconsequential based on the mood inside the aircraft and whether they were aware of their situation. Chances are they were all quite aware of the futility of inflating life jackets, which would not support a possible ditching attempt.

At any rate, this new theory brings up new questions. Earlier speculation centered on the condition of the bodies being indicative of an in-flight breakup, which would trend towards a scenario where the tail fin separated well ahead of impact. It now appears to have been wrong, or at least they are not speculating as to whether earlier evidence was misinterpreted.

Logic would suggest that if the tail fin was located close to the impact they should be able to estimate it's displacement using drift buoy data and find the primary debris field underwater. This suggests the black boxes may still be found. Any speculation as to whether it's better from a liability perspective for Air France or Airbus to have the tail remain intact until impact rather than earlier speculation that it was a source of inquiry is best left on the shelf until final disposition on the black boxes.

Yemenia 626

It now appears based on media descriptions that the aircraft was using the north approach to runway 02/20, runway 02, in order to perform a circling maneuver around to the south facing runway 20 due to strong winds. This would not be unusual, but making a circling approach at night to an island with strong southerly winds--which would have been downwind on the tail during the procedure turn--could end up being part of the explanation. Here is the approach plate:

Here are the weather observations:
FMCH 300000Z 21025G35KT 9999 FEW020 25/17 Q1016 TEMPO 19014KT
FMCH 292300Z 21025G35KT 9999 FEW020 25/16 Q1017 TEMPO 18015G30KT
FMCH 292200Z 18022G33KT 9999 FEW020 24/17 Q1018 NOSIG
That means there were a few clouds around 2000 feet (but it was mostly clear) and the winds were from the south at sustained 25-29 mph with gusts from 38-40 mph.

The fact that a passenger survived suggests the angle of attack on impact was much less severe than AF 447, perhaps even similar to this event.

As to the initial confusion over whether they'd found black boxes, that's easily explained by press or airline spokespeople misunderstanding the difference between an ELT beacon and the black box pingers. ELTs are designed to help search and rescue locate overdue or missing aircraft. They will almost certainly find the black boxes in this case with the debris pinpointed in shallower water.

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