Flight 370 was last detected flying over a small island hundreds of miles from the flight's usual route, a Malaysian official said.

(CNN)-- Malaysia Airlines Flight 370 was hundreds of miles off course, traveling in the opposite direction from its original destination and had stopped sending identifying transponder codes before it disappeared, a senior Malaysian Air Force official told CNN Tuesday. If correct, these are ominous signs that could call into question whether someone in the cockpit might have deliberately steered the plane away from its intended destination, a former U.S. aviation investigator said. "This kind of deviation in course is simply inexplicable," said Paul Goelz, former managing director of the National Transportation Safety Board. However, veteran pilot Kit Darby, president of Aviation Information Resources, told CNN's Wolf Blitzer that mechanical problems could still explain everything: A power failure would have turned off the main transponder and its backup, and the plane could have flown for more than an hour, he said. According to the Malaysian Air Force official, who declined to be named because he is not authorized to speak to the media, the plane's transponder apparently stopped working at about the time flight controllers lost contact with it, near the coast of Vietnam. The Malaysian Air Force lost track of the plane over Pulau Perak, a tiny island in the Straits of Malacca -- many hundreds of miles from the usual flight path for aircraft traveling between Kuala Lumpur and Beijing, the official said.