Cmdr. William Marks, a spokesman for the U.S. 7th Fleet, said finding the plane was like trying to locate a few people somewhere between New York and California.
Malaysian officials said early in the search that they suspected the plane backtracked and flew toward the Strait of Malacca, just west of Malaysia. But it took a week for them to confirm Malaysian military radar data that suggested that route. On Tuesday, Thai military officials said their own radar showed an unidentified plane, possibly Flight 370, flying toward the strait beginning minutes after the Malaysian jet's transponder signal was lost.
Air force spokesman Air Vice Marshal Montol Suchookorn said the Thai military doesn't know whether the plane it detected was Flight 370.
Thailand's failure to quickly share possible information about the plane may not substantially change what Malaysian officials now know, but it raises questions about the degree to which some countries are sharing their defense data.
Flight 370 took off from Kuala Lumpur at 12:40 a.m. Malaysian time March 8 and its transponder, which allows air traffic controllers to identify and track the airplane, ceased communicating at 1:20 a.m.
Montol said that at 1:28 a.m., Thai military radar "was able to detect a signal, which was not a normal signal, of a plane flying in the direction opposite from the MH370 plane," back toward Kuala Lumpur. The plane later turned right, toward Butterworth, a Malaysian city along the Malacca strait. The radar signal was infrequent and did not include any data such as the flight number.
When asked why it took so long to release the information, Montol said, "Because we did not pay any attention to it. The Royal Thai Air Force only looks after any threats against our country." He said the plane never entered Thai airspace and that Malaysia's initial request for information in the early days of the search was not specific.
"When they asked again and there was new information and assumptions from (Malaysian) Prime Minister Najib Razak, we took a look at our information again," Montol said. "It didn't take long for us to figure out, although it did take some experts to find out about it."
The search area for the plane initially focused on the South China Sea, where ships and planes spent a week searching. Pings that a satellite detected from the plane hours after its communications went down eventually led authorities to concentrate instead on two vast arcs — one into central Asia and the other into the Indian Ocean.
Malaysia said over the weekend that the loss of communications and change in the aircraft's course were deliberate, whether it was the pilots or others aboard who were responsible.
Malaysian police are considering the possibility of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board, but have yet to give any update on what they have uncovered.
Investigators had pointed to a sequence of events in which two communications systems were disabled in succession — one of them before a voice from the cockpit gave an all-clear message to ground controllers — as evidence of a deliberate attempt to fly the plane off-course in a hard-to-detect way. On Monday, they backtracked on the timing of the first switch-off, saying it was possible that both were cut at around the same time, leading to fresh speculation that some kind of sudden mechanical or electrical failure might explain the flight going off-course.
Malaysia Airlines CEO Ahmad Jauhari Yahya said it was not out of the question that there was some kind of problem aboard the plane, though he noted it still was intact enough to send a signal to a satellite several hours later.
As further confirmation that someone was still guiding the plane after it disappeared from civilian radar, airline pilots and aviation safety experts said an onboard computer called the flight management system would have to be deliberately programmed in order to follow the pathway taken by the plane as described by Malaysian authorities.
"If you are going to fly the airplane to a waypoint that is not a straight ... route to Beijing, and you were going to command the flight management computer and the autopilot system, you really have to know how to fly the airplane," said John Gadzinski, a U.S. Boeing 737 captain.
"If you were a basic flight student and I put you in an airborne 777 and gave you 20 minutes of coaching, I could have you turn the airplane left and right and the auto throttle and the autopilot would make the airplane do what you want," he said. "But to program a waypoint into the flight management computer, if that is what they flew over, is a little bit harder."