Sunday, June 5, 2011

Surreal reflections on AF 447


I flew from Paris to Sao Paulo yesterday on an Air France Airbus 330-203 (F-GZCJ) that in the previous seven days had been flown routinely between Paris and Riyadh; Paris and Rio de Janeiro; Paris and Abidjan, Ivory Coast; Paris and Cairo and Paris and Senou, Mali, West Africa. This aircraft returned to Paris last night and is on its way to Abu Dhabi as I write this. The flight met all my expectations – departed and arrived on time and the cuisine on board was excellent.

It was however, a surreal experience because I was travelling almost two years to the day after Air France flight AF 447 from Rio to Paris abruptly crashed into the Atlantic Ocean near the Equator on 1 January 2009 without broadcasting an emergency call. The jet had been flying normally for over three hours when its autopilot and auto accelerator abruptly disengaged at 11,000 metres leading to the death of 228 people from 32 countries. These sophisticated instruments are more complex that merely controlling heading, altitude and speed. They can control the character of a climb or landing. My flight also flew at 11,000 metres. At that altitude above sea level humans cannot breathe unaided. Aircraft require atmosphere – the bubble of air that surrounds the earth that is held in place by the earth’s gravity.

I first flew to Brazil in August 1988 and several times subsequently and I have always noted episodes of turbulence close to the Equator.  AF 477 had reached an area known as the Intertropical Convergence Zone, next to the Equator, where tall thunderstorms in a configuration not dissimilar to a very tall chimney, create icy, windy conditions that often causes turbulence. When I was at school this phenomena was called The Doldrums where the winds of the Northern and Southern Hemisphere converge.  The Doldrums traditionally caused sailors more difficulty than aviators because of the absence of wind to propel sailing boats.

The AF 447 crew had navigated around an anticipated thunderstorm even though there was speculation that they flew directly into it.

It emerged last week that the black box has been recovered and that a combination of turbulence, faulty instrument readings and a stalled engine caused this aircraft to fall at a rate of 3,000 metres per minute from the normal cruising altitude of 11,000 metres in a four-minute period. The wreckage sunk to a depth of four kilometres under the Atlantic Ocean. The stall warning sounded in the aircraft twice indicating that aerodynamics were not sustaining the aircraft and that control was being lost.

There had been speculation that the crew had steered the Airbus into a storm, where water was sucked into a configuration like a giant chimney that converted water into indecipherable ice crystals that are not detected on radar. The aircraft apparently experienced what experts call a deep stall and the wreckage was scattered ten kilometres from its last recorded location.

There is a suggestion that Air France pilots had not at that time been adequately briefed on how to deal with speed sensor failure and there had been several episodes of this occurring in Airbus aircraft. The evidence available shows that the crashed aircraft pulled steeply upwards after the speed sensor failure and this could have caused a stall.

Having discovered the black box on 1 May last, the French Accident Investigation Bureau (BEA) is now able to reveal the sequence of events leading to the crash of flight AF447. This analysis replaces the assumptions that have been made over the past two years.

It appears that the flight deck crew was monitoring the changing weather conditions and thus altered the flight path, that the initial problem was the failure of the speed probes which led to the disconnection of the autopilot and the loss of the associated piloting protection systems, and that the aircraft stalled at high altitude. It also appears that the flight captain quickly interrupted his rest period to regain the cockpit.

Compensation claims will be attributable to whoever is blameworthy for the accident.  Both Air France and Airbus could be prosecuted for negligent manslaughter

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