JAKARTA: Unlike Malaysian Airlines flight MH370, the spectre that haunts the world of aviation even as it stresses the relative safety of flying, this disappearance has not been accompanied by puzzling patterns of behaviour from the flight deck or radar. But on Sunday night, for the second time in less than a year, hundreds of passengers appeared to have perished mid-flight without any immediate explanation.
The disappearance of the plane without a distress call leaves little clues but makes a midair explosion or some other catastrophic failure a theoretical possibility. In the realm of speculation, a parallel cited on pilots’ forums and by aviation experts was the crash of Air France flight 447, which was lost at sea in 2009 via a combination of severe weather, technical failure and pilot disorientation.
The European Aviation Safety Agency earlier this month issued an emergency airworthiness directive for planes in the Airbus A320 family after an incident when computers on an A321 tried, needlessly, to prevent a stall at the top of a climb by automatically pushing the nose downwards, after sensors iced up. But flight tracking data suggests the path of QZ8501 would not have triggered a similar anomaly.
Despite the offers of international assistance in the hunt for the aircraft, wreckage from the flight is expected to be found once the planes from Indonesia and its neighbours resume their visual search on Monday morning.
Most of the nine major fatal accidents in the 26-year history of this model of plane, the Airbus A320, have occurred on takeoff or landing or final approach. The manufacturer said one of these 6,000 short-haul workhorses, a twin-engine plane seating up to 180 passengers, takes off or lands somewhere in the world every few seconds. The plane that went missing between Surabaya in Indonesia and Singapore was delivered to AirAsia in 2008 and had recorded 23,000 flight hours on 13,600 flights, according to Airbus. It had undergone its last scheduled maintenance on 16 November.
AirAsia carriers have had a clean safety record, although Indonesia’s faltering standards at one point saw all of its carriers barred from European airspace by the EU on safety grounds.
Until any wreckage, and particularly the black boxes, are located, the most salient detail of this incident appears to be that the pilots had asked to change course to avoid cloud in the latter moments of the flight.
Jakarta air traffic control had granted a request for the plane to ascend to 38,000ft. Satellite images show heavy thunderstorms in the vicinity. Although the request to go higher to avoid bad weather is not an unusual one, pilots are aware that flying over a thunderstorm will not necessarily mean clearing it: according to forecasters at Indonesia’s meteorology agency, dense storm clouds were detected up to 44,000ft when the plane was reported to have lost contact. Turbulence and strong gusts of winds would be likely.
Frozen sensors corrupted the instrument readings and led pilots to believe they were losing height, and misguided attempts to correct the plane’s course led to a fatal stall.
Doug Maclean, an aviation expert and former air traffic controller, said that while contact was lost at 6.17am, an emergency was only declared at 7.24am – a delay reminiscent of the Malaysian response, although one unlikely on this occasion to alter the outcome. Pilots were in contact with air traffic control until the last minute.
David Learmount, a former pilot and now operations and safety editor of Flight Global, said: “Storms can be very, very powerful indeed and rip a medium-sized aeroplane completely apart, that’s why a pilot will routinely ask to divert around them.”
Maclean said: “I’ve seen very large planes shifted anything up to 4,000ft by turbulence; a thunderstorm often extends far over a cloud. Pilots are very wary of flying above the top of a storm because the air could be very violent. If you’ve taken the airplane up to 38,000ft, you’re into slightly marginal conditions for the airplane to fly in … If you’re also hit by turbulence, you could more easily see the aircraft out of control.”
Another plane had passed through roughly the same airspace at the same level earlier: the course was not unusual, Maclean said. But at higher altitudes and lower temperatures, the margins for error in flight are tighter. “A smaller loss of speed would be critical. Purely speculatively, something could have happened dramatically in that little marginal envelope to affect the plane very significantly and put it in an unflyable position.”