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— General Manoj Pande, Indian Army Chief

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My compliments to SP Guide Publications for informative and credible reportage on contemporary aerospace issues over the past six decades.

— Air Chief Marshal V.R. Chaudhari, Indian Air Force Chief

Cause Not Clear

Issue: 06-2009By Air Marshal (Retd) V.K. BhatiaIllustration(s): By 294.jpg

In the early hours of June 1, an Air France Flight en route to Paris from Brazil crashed into the Atlantic Ocean, killing all 228 people onboard. A month later, officials of France’s Bureau d’Enquêtes et d’Analyses (BEA) say they still don’t know what caused Airbus Flight AF447 to plunge into the ocean barely hours after it had taken off from Rio de Janeiro. BEA officials are also grappling with another question: why the plane was reported missing a full seven hours after reporting its last radio contact? Alain Bouillard, the BEA official leading the probe, has confirmed search teams will continue to try and locate the recorders’ audible beacons using ultra-sensitive undersea microphones until July 10, when batteries on the “pingers” will almost definitely have died.

Deadliest in the history of Air France, the AF447 disaster is also the first fatal crash involving the airline’s aircraft since the AF4590 Concorde supersonic mishap in July 2000.

The aircraft, an Airbus A330-200, powered by two General Electric CF6-80E1 engines, was only four years old. Even though it had accumulated 19,000 hours in its short service life, it had also undergone major overhaul in April-May and was presumably in impeccable condition when it took off on May 31. The aircraft had departed from Rio’s Galeao International Airport at 19:03 (22:03 UTC or GMT), with a scheduled arrival at its destination 11 hours later. The last verbal contact with the aircraft was at 01:33 UTC off Brazil’s northeastern coast which indicated that the flight was progressing normally at FL 350 (35,000 ft altitude). The aircraft went out of Brazil Atlantic radar surveillance at 01:48, having crossed the equator into northern hemisphere. This was also the time when the aircraft was entering the Intertropical Convergence Zone. That things started to go wrong in rapid succession soon after was evident from the messages automatically generated by the onboard Aircraft Communication Addressing and Reporting (ACARS) maintenance system. The transcripts indicate that between 02:10 and 02:14, as many as five failure reports and 19 warnings were transmitted. The warnings included disengagement of autopilot and auto-thrust systems. The last transmission at 02:14 indicated an ominous “cabin vertical speed warning”, indicating that the aircraft was being subjected to massive variations in vertical speed.

While the search for the ‘Black Boxes’ (Flight Data and Cockpit Voice Recorders), presumed to be lying as deep as 5 km below the ocean surface, is still on, what is baffling investigating agencies is the total lack of voice reporting by the crew in the last minutes of the flight even when the aircraft was experiencing a string of failures. Is it possible the catastrophic occurrence which caused the flight to disappear happened so suddenly that the pilots had no chance to react?

A detailed meteorological analysis of the area surrounding the flight path showed a string of mesoscale convective systems extending upward to an altitude of 51,000 ft through which the flight most likely flew for as long as 15 minutes before disaster struck. It is quite possible that the aircraft’s pitot heads might have partially clogged due to the presence of rime ice at that altitude corroborated by the fact that the first message transmitted by the ACARS pertained to faulty airspeed sensors. But, notwithstanding the outcry against the less-than-adequate existing pitot heads and the need to replace these with new systems with better heating, it is hardly likely that the faulty speed indications would alone lead to such an accident.