PPRuNe Forums - View Single Post - AF447
Thread: AF447
View Single Post
Old 6th Jun 2009, 11:05
  #302 (permalink)  
lear60fellow
 
Join Date: Jan 2008
Location: germany
Posts: 146
Likes: 0
Received 0 Likes on 0 Posts
I just read in this Spanish forum ( Una hipótesis a tener en cuenta (esta sí)) a theory based on an actual situation that happened to an IBERIA flight on May 2001, the actual captain was flying B747 and retired flying A340, it´s quite interesting as it happened in the same area. I will translate the basics.

"Flying from Buenos Aires we overflew Rio de Janeiro and followed the same route that AF474 was flying when the accident happened. Crossing the ITCZ at FL370 with moderate to heavy turbulence in a 1-2 minutes period we experienced a sudden increase in air temperature, from -48ºC to -19ºC. The consecuences were that we passed flying with a margin of 10.000kgs to being 15.000kgs above maximum weight and out of limits at that temperature and Flight Level. Inmediately the aircraft experienced a stall situation with lots of buffering. I desconected the AP y and we descended 4.000ft flying in the coffin corner having at the same time high and low speed stalls. If I wouldn´t have disconnected the AP and flew it manually we would be now into the deep ocean. The AP tried to maintain at all times the altitud using engines and that was impossible and the consecuences would have been an abnormal position of the aircraft and spacial desorientation to recover it at night and into the clouds.

I would describe it as an enormous 40 miles radius of hot air on the begining of a developing storm ascending to high altitude. After 5 min everything became normal and we continued our flight.

AIRBUS criteria says that flying into moderate or heavy turbulence "YOU MUST NOT DISCONET THE AP" but the fenomenom is not described or even contemplated and if the crew of AF474 did not disconneted the AP probably they had a situation similar to the one I experienced. The theory is that ACARS messages were sent due to this situation:


New information provided by sources within Air France suggests, that the ACARS messages of system failures started to arrive at 02:10Z indicating, that the autopilot had disengaged and the fly by wire system had changed to alternate law. Between 02:11Z and 02:13Z a flurry of messages regarding ADIRU and ISIS faults arrived, at 02:13Z PRIM 1 and SEC 1 faults were indicated, at 02:14Z the last message received was an advisory regarding cabin vertical speed. That sequence of messages could not be independently verified.”

On basics it means: the AP disconnects when gets to the limit but the aircraft is already on an abnormal position, then is reverts to alternative flight control, then is followed by ISIS and Interial failures, then PRIM1 + SEC1 computer failures and finally a sudden decreas in cabin pressure (when the aircraft is already divided in parts), multimple electronics failures as the aircraft is desintegrating.

All this happens between 2:10Z and 2:14Z
lear60fellow is offline