ANALYSIS:Lightning strike has certainly brought planes down before but modern aircraft routinely survive such incidents unscathed, writes GERRY BYRNE.
WHAT CAUSED the Air France Airbus jet simply to vanish from the skies northeast of Brazil with such appalling loss of life?
Pan Am Flight 214 crashed in December 1963 killing 81 people. In 1971, 91 people died when a fuel tank aboard Lansa Flight 508, a Lockheed Electra L-188A turboprop, exploded after a lightning strike. But modern aircraft can usually resist lightning strikes: the average aircraft can expect to be hit by lightning at least once a year without mishap.
That’s not to say that fuel tank explosions are a thing of the past: many hundreds of Boeing aircraft still fly with a lethal configuration where the air conditioning system effectively uses fuel in the centre-wing tank as a coolant. On a hot day this can heat fuel vapours in a half-full tank to the extent that, as in TWA-800, which blew up over Long Island Sound in 1996, it becomes an explosion waiting to happen.
But Airbus has always protested that its air conditioning and fuel tanks are thoroughly separated and no wires (suspected of providing the spark that downed TWA-800) pass through its fuel tanks.
There has also been renewed criticism of allowing aircraft with two engines (as opposed to four engines) to fly the Atlantic. This is an old debate, which has long been decided in favour of the twins.
Severe icing is also a possibility: aircraft in thunderstorms can encounter freezing rain and deluges from tropical storms have been known (rarely) to quench a jet engine.
Turbulence cannot be ruled out either. Tremendous updrafts and downdrafts of air within a cumulonimbus thunder cloud have wrecked jets.
Near Falls City, Nebraska, in August 1966 the pilot of a Braniff Airways BAC 1-11 jet, naively believing the new jets could cope with anything, entered a thunderstorm at low altitude. Investigators estimated the aircraft was struck by gusts of at least 100mph which first ripped off the tail, then a wing.
The tail, part of a wing and the engines were fatally ripped off a BOAC Boeing 707 when it flew into fierce turbulence in the lee of Japan’s Mount Fuji earlier the same year.
In 1964 a massive US Air Force B-52 bomber lost three quarters of its tailfin and was lucky to survive being savaged by turbulence above Colorado.
Turbulence in the severe thunderstorms known to have been straddling Flight AF447’s route may have been of similar ferocity but wiser modern pilots either flying above or around them.
However, meteorology reports from the area suggest the turbulent clouds towered above 40,000 feet, close to the flight limits of an A330, perhaps leading the pilot to attempt to fly through them using weather radar for guidance. In his last radio contact, the pilot reported “hard” turbulence. Perhaps his radar failed, causing him to unwittingly fly into danger. Whatever happened to Flight AF447 was catastrophic, leaving the pilots unable to declare a Mayday.
A mid-air break-up could have been caused by severe turbulence, or a bomb that might have disabled the aircraft severely without causing an immediate break-up. Whatever the cause, the disabled aircraft may have flown some distance before crashing into the sea. Wreckage has been found hundreds of miles from where the aircraft was last reported.
But the possibility still remains that some hitherto undetected flaw has emerged in an otherwise wonderful airplane. It’s happened before. Early Boeing 747 aircraft were found to have a serious structural weakness where the nose joined the fuselage. A serious flaw emerged in the Boeing 737 rudder hydraulics after two fatal crashes, in Colorado Springs in 1991 and Pittsburgh in 1994, when the rudder suddenly deployed and caused the aircraft to spin out of the sky.
Warnings were issued about the reinforced plastic tailfin of the earlier model Airbus A300 when one snapped off after vigorous use during take-off leading its crash on Queens, New York, killing 265 in November 2001.
Or did something else occur which caused this aircraft to misbehave?
Investigators in the USA are still puzzling over a series of so-called “rollback” incidents when turbofan engines, similar to those on the doomed jet, alarmingly went into idle speed, in some cases when taking off. Fortunately, crashes were avoided. Unexpected ice blockages in the fuel lines are suspected of being the cause of the crash landing of a British Airways Boeing 777 in Heathrow in January 2008 although links have also been made with the US rollback incidents.
Modern aircraft – and Airbus is a leader in this field – are heavily dependent on computers to control their complicated systems. Could software be at fault?
Australian investigators are still trying to make sense of an incident last October where a Qantas Airbus A330 twice unexpectedly and rapidly dived hundreds feet in seconds, injuring dozens of passengers. Initial findings suggest that the aircraft was responding to faulty inputs suggesting the aircraft was not flying level, and about to stall, when in fact it was perfectly configured. Could something similar have happened to Flight AF447? And if it did, did the pilots react appropriately?
Last February a Colgan Airlines Bombardier Q400 approaching Buffalo, New York, stalled and crashed killing 50. The flight computer put the aircraft into a dive to increase speed, as the iced-up aircraft was about to stall. But, instead of increasing engine power, then levelling out, the pilot pulled back on the controls to put the nose up. It led to his death. Indeed, pilot error has for years been the leading cause of air crashes.
Without accurate data from the still-to-be-recovered Air France AF447 black boxes, guessing winning horses is probably more profitable than attempting to predict the cause of an air disaster.
Modern aircraft are so safe and the process of investigation to prevent repeats so thorough that only one prediction is probably accurate.
Like the last year’s BA crash at Heathrow, investigation of this one is likely to conclude that it was caused by a chain of events the likes of which have never occurred before.
Gerry Byrne is a freelance journalist specialising in aviation