KUALA LUMPUR, March 13 — A missing Malaysian airliner kept flying after it dropped off controllers’ radar screens, raising new questions about whether foul play was involved, according to people familiar with data gathered in the inquiry.

Aviation specialists investigating last week’s loss of Flight 370 say evidence gathered so far suggests that the plane travelled west over Malaysia, possibly continuing for hours, according to the people, who asked not to be identified discussing an active probe. One person said US investigators increasingly suspect the act was criminal, without elaborating.

The latest evidence adds a new note of mystery to the disappearance of the Malaysian Airline System Bhd. plane carrying 239 people that vanished while flying from Kuala Lumpur to Beijing. Data compiled so far show no evidence of a crash near the Malaysian peninsula, the people said.

Radar signals sent from the ground continued to reflect back from the plane after its transponder went dead as the aircraft headed north from Malaysia toward Vietnam, said the people, who weren’t permitted to speak publicly about the probe. After the transponder shut off, making it harder to follow on radar, the plane turned left toward the west instead of continuing on its path.

An automatic system that sends data about the health of the plane’s engines may also have continued to function, indicating that the aircraft was being operated intentionally, the people said. That suggests the Boeing Co. 777-200 may have been flown off course with the intent to fly undetected, by the pilots or hijackers.

Fuel reserves

The 777 had enough fuel to fly the 2,700 miles (4,345 kilometres) to Beijing and reserves to fly to a diversion airport. That meant it was capable of flying at least 2,000 miles after it changed course. The Wall Street Journal reported that the plane stayed in the air for four hours after reaching its last confirmed location.

The aircraft’s transponder normally sends radio beacons to ground radar stations making it easier to follow and providing other information, such as its identity and altitude. While it’s possible for such a transponder to malfunction or for pilots to accidentally switch it off, it is highly suspicious for the device to fail at the same time a plane makes an abrupt change of course.

The plane continued to fly west toward the Andaman Sea, only dropping off Malaysian radars as it reached the end of their range, the people said.

No debris

The information raises as many questions as it answers about the case and was still being assessed by officials, the people said.

With the search on its sixth day, authorities still have produced no evidence to show what happened to Flight 370 en route to Beijing from Kuala Lumpur on March 8. Malaysia’s military is looking into an unexplained radar blip that’s added to the mystery.

A Vietnamese plane sent this morning to search an area where the Chinese satellite spotted floating objects didn’t find anything, said Lai Xuan Thanh, head of the Civil Aviation Authority of Vietnam. — Bloomberg