马航飞机失联原因难于调查

Traditionally regarded as one of the safest planes in the skies, the Boeing 777's reputation will have been damaged by the second fatal crash in less than a year.

波音777飞机一直被认为是最安全机型之一，但不到一年时间里发生第二起致命坠毁必然会使其名声受损。

There are around 1,000 Boeing 777s in service, and the plane is a long haul workhorse, plying some of the longest routes.

It entered service in 1995 and the National transportation Safety Board, which is responsible for monitoring US-made aircraft, has logged fewer than 60 incidents.

But the recent record has been more patchy（不调和的） with two major incidents - a crash at San Francisco airport last July, which claimed three lives, and the crash-landing of a British Airways 777 at Heathrow in January 2008.

But the Malaysian disaster is very different from both the BA incident and the crash involving a Asiana Airlines flight at San Francisco International Airport in July.

Both the BA and Asiana accidents occurred shortly before landing, while the Malaysia airlines plane disappeared off the radar during the early stages of the trip.

The accident at San Francisco in July was attributed to pilot error which led to the engines being set to idle because he believed the computer would maintain sufficient speed to keep the plane up in the air.

But initial reports suggest that Zaharie Ahmad Shah, the 53-year-old Malaysian airlines pilot, was hugely experienced - having joined the carrier in 1981 and with 18,365 hours in the cockpit under his belt.

The BA crash landing, which did not result in any fatalities, was finally found to have been caused by a blockage in the fuel line feeding the engine.

Simply put the aircraft had the aviation equivalent of a cardiac arrest because some of the fuel failed to melt and blocked the supply line at the end of a long flight from Beijing to London, during which the plane travelled through unusually cold airspace over Siberia.

This crash has echoes of the disaster in which 288 people on board an Air France Airbus 330. That plane, another long-haul workhorse, crashed into the Atlantic en-route from Rio de Janeiro in June 2009 killing 228 people.

A variety of explanations have been given for the Air France crash, with investigators finding that the plane's speed sensors were giving an incorrect reading.

But with this crash involving a different aircraft, it will take several months before investigators can ascertain the cause.