From the beginning, a fog of speculation has swirled around the disappearance of Malaysia Airlines Flight 370. There have been the continual false reports of wreckage being found. The presence aboard the flight of passengers using stolen passports immediately raised the issue of terrorism—though exactly why this airline would have been targeted is baffling, nor has there been any claim by a terrorist group. Now Malaysian authorities have said that one of the passengers with a stolen passport was an Iranian seeking asylum in Europe (and this has opened up a tangential security concern about the volume of stolen passports and their widespread use). Then there is the uncertainty of where exactly the Boeing 777 was when it disappeared—we have no reliable timeline of its course from takeoff and exchanges between controllers and the crew. The Malaysians have now added to this confusion by raising the issue of “psychological” problems among either the crew or passengers.
At a time when surveillance intrudes into the most intimate details of our lives, it seems inexplicable that an airplane this large can vanish into thin air in an instant without explanation.
Given this perplexing picture, what, if anything, looks like a firm fact?
Whatever happened was instantaneous. There was no distress call from the pilots, and no previous hint of a technical problem.
This leaves five possible scenarios:
1. Bomb in the cabin.
2. Bomb in the cargo.
3. Accidental explosion in the cargo hold.
4. Explosion in one of the engines.
5. “Explosive decompression” where the fuselage breaks apart suddenly and catastrophically.
It has been established that U.S. satellite surveillance aimed at detecting the flash from missile launches and other possibly clandestine military activity did not detect any explosive flash in the South China Sea region at the time. This may be a tenuous deduction but it would, if reliable, rule out the first three options, leaving two that are mechanical and would not necessarily cause a flash big enough to be detected from space (although in the case of an engine explosion there could well be fuel fire).
There is a recent case of an engine explosion seriously jeopardizing a flight—Qantas Flight 32 was on its initial climb from Singapore in 2012 when one of its Rolls-Royce Trent engines exploded. Shrapnel tore through the Airbus A380, causing severe damage. But, unlike the twin-engine Boeing 777, the A380 had four engines and three of them, although seriously degraded, provided sufficient power for the pilots to make a hairy emergency landing.
Engine failures of this kind are extremely rare. The captain of the Qantas A380 pointed out that an engine is not expected to fail during at least 50,000 operating hours and, in practice, they can operate for as many as 300,000 hours without failing. In fact, the reliability of the jet engine is the single most influential development behind the vast improvement in air safety.
It turned out that the engine on the Qantas airplane had a manufacturing fault.
We now come to the fifth scenario: explosive decompression. An airplane cabin is, basically, a pressure vessel. In order to make the cabin climate acceptable at cruise altitude of 36,000 feet, the air inside the cabin is kept at the equivalent of 8,000 feet. As the airplane climbs, the difference in pressure between the air in the cabin and the air outside increases.
As a result, the airplane structure has to be designed to contain this difference—it’s the reverse of what happens to a submarine diving to depth where it’s the outside pressure on the hull that has to be resisted.
When the Boeing 777 was designed in the 1990s, it reflected everything Boeing had learned about structural integrity, including new metals and alloys. Indeed, the robustness of its fuselage was proved last year in the crash of an Asiana 777 at San Francisco—the only previous 777 incident involving fatalities—where, in spite of an horrendous impact, the majority of passengers were able to survive. (That crash was caused by pilot error).
Boeing does have one airplane with a long record of stress failures in its fuselage, the 737. Its fuselage was developed from a 1960s technology. Very early in its history, there was a fatal crash as a result of decompression as well as another where the cabin roof was ripped off. As recently as 2011, there was another cabin roof failure, on Southwest Airlines Flight 812—in spite of numerous upgrades of the fuselage structure.
However, integrity of the fuselage structure is not an absolute guarantee that an explosive decompression will not occur. Pressurization exerts forces on any potential weak point, and that includes doors and cargo hold latches.
For example, in 1989 a United Airlines Boeing 747 suffered a failure in a cargo hold door over the Pacific. Nine business-class passengers, still strapped in their seats, were sucked out of the airplane. The 747 was badly crippled but the pilots were able to get it back to Honolulu on the power of the two left engines.
The proficiency of ground handlers matters here—the cargo holds are heavily used and the doors are designed so that the flight crew must always see on their preflight check that everything is secure. The same thing is true for the cabin crew and their supervision that the cabin doors are correctly closed and that the air seals are working. In January, a Singapore Airlines Airbus A380 carrying 467 passengers en route from London to Asia was diverted to an emergency landing in Azerbaijan when it experienced a cabin-pressure failure due to a faulty door seal.
So what might this indicate about the fate of Flight 370?
We do know that it vanished soon after it reached its cruise altitude of 36,000 feet. In that respect it accords with many previous experiences of cabin decompression, the moment when the pressure difference becomes most acute. That was when, for example, the cabin roof ripped off Southwest Airlines Flight 812. This could, however, just be coincidence.
Looking for the explicable in a case that seems so inexplicable is what the air crash investigators have to do. And they can’t even begin that task until there is physical evidence to go on—first the critical evidence from the flight data recorders and the cockpit voice recorder, and then the story to be told by every piece of the wreckage.