came on July 6 last year when Asiana Airlines Flight 214 struck a seawall on landing in San Francisco, killing three people.

U.S. planemaker Boeing has declined to comment beyond a brief statement saying it was monitoring the situation.

The disappearance of a Malaysian airliner about an hour into a flight to Beijing is an “unprecedented mystery”, the civil aviation chief said on Monday, as a massive air and sea search now in its third day failed to find any trace of the plane or 239 people on board.

Dozens of ships and aircraft from 10 countries scoured the seas around Malaysia and south of Vietnam as questions mounted over possible security lapses and whether a bomb or hijacking attempt could have brought down the Boeing 777-200ER which took off fromto indicate that the aircraft is likely to have disintegrated at around 35,000 feet,” said the source.

Asked about the possibility of an explosion, the source said there was no evidence of foul play and that the aircraft could have broken up due to mechanical causes.

Still, the source said the closest parallels were the bomb explosions on board an Air India jetliner in 1985 when it was over the Atlantic Ocean and a Pan Am aircraft over the Scottish town of Lockerbie in 1988. Both planes were cruising at around 31,000 feet at the time.

The United States extensively reviewed imagery taken by American spy satellites for evidence of a mid-air explosion, but saw none, a U.S. government source said. The source described U.S. satellite coverage of the region as