The erratic movements of the aircraft after it diverted course and flew over Malaysia also raise questions about why the military did not respond to the flight emergency. Malaysian officials have acknowledged that military radar may have detected the plane, but have said they took no action because it did not appear hostile.

A week after the jet’s disappearance, the Malaysian authorities have shared few details with American investigators, frustrating senior officials in Washington. “They’re keeping us at a distance,” one of the officials said.

But investigators in Malaysia and the United States recently began receiving additional data about the plane and anticipate more over the weekend, according to a senior American official. “It’s gotten better and better every day,” the official said, referring to information from the plane’s manufacturer, satellites and military radar. “It should provide more clarity to the flight path. It’s not a given, but it’s a hope.”

Because the plane stopped transmitting its position about 40 minutes after takeoff, military radar recorded only an unidentified blip moving through Malaysian airspace. Certain weather conditions, and even flocks of birds, can occasionally cause radar blips that may be mistaken for aircraft. The Malaysian authorities said they were still studying the signals to determine whether they came from Flight 370.

But the person who examined the data said it left little doubt that the airliner flew near or through the southern tip of Thailand, then back across Peninsular Malaysia, near the city of Penang, and out over the sea again. That is in part because the data is based on signals recorded by two radar stations, at the Royal Malaysian Air Force’s Butterworth base on the peninsula’s west coast, near Penang, and at Kota Bharu, on the northeast coast. Two radars tracking a contact can significantly increase the reliability of the readings.