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article imageDetailing the last 4 minutes of crashed Air France flight AF447

By Michael Cosgrove     Jun 4, 2009 in World
Precise details are emerging of the automatic distress messages sent by the doomed plane in its final four minutes before communications were lost. They describe a swift and catastrophic sequence of events, possibly ending in the plane’s vertical descen
Several European papers, including ‘Liberation’ here in France are reporting information divulged by a source within Air France that details the content of the last automatic messages sent by the plane.
Many modern planes are equipped with automatic message and distress message systems that collate data from hundreds of parameters on the plane and send them back to the plane’s operator, in this case Air France. Their message reception facilities are in Paris.
The automatic message system kicks in as soon as aircraft systems are switched on and only stop when the systems are switched off or stopped by breakdown, in other words from the moment the crew activates systems before a flight to the moment they leave the plane at its destination.
The objective of this system is to send details of everything that happens on the plane, from in-flight entertainment use to engines, in order to help analyse anomalies that may occur during a flight. Many messages are sent during a normal flight. For example, a slight drop in cabin temperature or pressure, not at all dangerous in itself but maybe indicative of a minor fault, would be relayed to Paris for analysis which could be used in corrective maintenance action being carried out on the plane concerned.
The information in press reports details some, but not all, of the messages sent during the last four minutes of flight AF447's transmissions. They indicate rapid and progressive failure of all systems on the plane and finally its depressurization.
The first indications of abnormal conditions on flight AF447, in this case weather conditions, were sent in a manual message by the pilot at 11pm local (Brazil) time. He indicated that the plane was crossing a large zone of dense black cumulo-nimbus clouds that were highly-charged with electricity.
Exactly 10 minutes later, a cascade of problems began to occur:
23h10: The first Alert message was “Autopilot Disengaged.” This means that the automatic pilot, which would normally be in use during routine mid-Atlantic flight, was disengaged, either by the pilot himself or automatically because of abnormal plane movement or other problems in order that the pilot and crew quickly regain manual control of the plane’s movement. At the same time another message indicated that the plane was flying on “Alternative Law” regime, which is an auxiliary back-up which automatically kicks in after an electrical system linked to flight mode configuration breaks down.
23h12: Two more crucial systems stop working. The first, the ‘Air Data Inertial Reference Unit,’ controls and displays data such as altitude and heading on visual displays. The second, called the ‘Integrated Standby Instruments System,’ is an auxiliary screen which shows data such as horizontal and vertical speed.
23h13: Damage to the plane’s crucial main computer, Prim 1, and to an auxiliary system, Sec 1, which controls the spoilers (the movable parts of wings which are used during take-off and landing). This type of plane, an Airbus A330-200, is equipped with automatic emergency back-up systems for Prim 1 and Sec 1, but they apparently did not kick in.
23h14: The last message, with a list of parameters including « Cabin Vertical Speed,» was sent. This message would indicate, amongst other things, that outside air had entered the cockpit, indicating a probable depressurization of the plane, that all electrical systems had broken down and that the plane may have been falling.
Efforts have resumed today to trace debris, and a French ship with ocean floor charting equipment is on its way to the zone. The ship is also transporting a submersible which is capable of descending to a depth of 6000 metres, which is the depth of the Atlantic in the area. Its job would be to trace the plane’s black boxes if possible.
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