Theories about the disappearance of Malaysia Airlines Flight MH370 range from dual engine failure of the aircraft to terrorism, from a mid-air collision to a suicidal pilot, from a fuel tank explosion to a hijacking.
The so-called “cruise” segment is by far the safest section of a flight, so the greatest mystery is how the aircraft disappeared without warning, and without the pilots sending a Mayday.
Airliners appear on radar screens as a collection of letters and numbers, giving the aircraft’s identity, its altitude, direction and speed, items broadcast by a device aboard the aircraft known as a transponder. A transponder that suddenly stops working leads to the suspicion that the aircraft has suddenly lost all electrical power, perhaps even exploded. But there may be other reasons.
In some aircraft it is possible for the pilots (or a cockpit intruder) to switch off the transponder and remove all references to the aircraft on air traffic control radar. It is still possible for the aircraft to be visible as an unidentified “blip”, but only on some types of radar. This might explain some reports that military sources spotted an aircraft heading away from the missing aircraft’s last known position.
Hijacking risk
If that report is true, and given the fact that two Iranians travelling on stolen passports were aboard, a hijacking has to be considered.
There are also suggestions it may have suffered a catastrophic mid-air break-up, so sudden as to cause all systems to stop working. Apart from a bomb, one cause might be explosive decompression.
Between 1952 and 1954, three UK-built Comet airliners crashed because of explosive decompression, whereby the planes burst almost like a balloon, due to the pressure difference between the cabin and the low-pressure air outside. Subsequent jets are tougher although there are still occasional occurrences.
The explosive decompression of a Japan Airlines Boeing 747 led to 520 deaths in 1985. In 1988, a Hawaiian stewardess died when a large section of the roof of an Aloha Airlines Boeing 737 peeled off in another explosive decompression.
The missing aircraft is a Boeing 777, one of the safest jets flying with no record of explosive decompression. Other types of decompression, caused by a technical failure of the pressurisation system, do not lead to fuselage damage but can still be serious. When pressurisation fails oxygen masks should drop down and must be donned immediately because at high altitude the body can have as few as 30 seconds of useful consciousness left owing to hypoxia, in which the brain is starved of oxygen. Without oxygen, unconsciousness quickly follows.
Pressurisation errors
There have been cases of this system failing and also of pilots deliberately turning cabin pressurisation off to conserve power when taking off from short runways, then forgetting to turn it on again. In 2005, 121 died when a Helios Airlines Boeing 737 crashed in Greece in an accident blamed on hypoxia caused by the pilots not realising the pressurisation system was turned off.
Fuel tank explosions are another cause of mid-air break up and led to the deaths of 230 in 1996 when a TWA Boeing 747 blew up over Long Island Sound, New York.
Fuel inerting systems to remove oxygen from fuel tanks were made mandatory for new aircraft designs in 2008 but the missing Malaysian airliner was built prior to that. Some aircraft have been retrofitted with fuel inerting systems but it is not known if one was in place on the missing aircraft.
The 777, like all twin-engined airliners, is designed to fly on only one engine and failure of both is usually thought unlikely.
Dual engine failure
However, a British Airways Boeing 777 lost power in both engines in 2008 when approaching a landing at Heathrow after a flight from China. Investigators discovered ice clogged fuel pipes caused the engines to stop.
One imagines the pilots would send out a Mayday warning if the engines stopped or the aircraft was affected by other, non-cataclysmic failures.
However, in the 2009 disappearance of Air France Flight 447 the three confused pilots on the flight deck sent no Mayday even though the stalled aircraft took minutes to hit the sea and the flight data recorder showed they were conscious until the impact.
Suicidal behaviour by pilots is not unknown and was blamed for the deaths of 321 in the loss of an Egyptair Boeing 767 over the Atlantic in 2009, and a 1997 Silk Air Boeing 737 crash in Indonesia.
Other possibilities are metal fatigue leading to wing or tail failures, but this is highly unlikely in a well-maintained aircraft of that age.
Gerry Byrne is an aviation, business and science journalist