A senior Chinese aviation official says officials can't confirm any link between the floating objects captured on Chinese satellite images to a Malaysia Airlines jet missing for more than five days.
"It is true that the satellite was launched and detected some smoke and what were suspected metal shreds about 37 kilometres southeast of Ho Chi Minh City," said Li Jiaxiang, chief of the Civil Aviation Administration of China. "But after some review, we cannot confirm that they belong to the missing plane."
The three objects of varying sizes were spotted in the sea off the southern tip of Vietnam and east of Malaysia on Sunday morning, near an oil rig off Vietnam where a New Zealand worker claimed to have witnessed a burning object in the sky about the time the missing flight is believed to have crashed.
The find had given hope that the tantalising mystery of the fate of the Boeing 777-200ER and its 239 people on board might soon be solved - but now it could be just another possible false lead.
RADAR DATA QUESTIONED
Meanwhile, a US aviation official is questioning the quality of the radar data that Malaysian military officials have cited in saying that MH370 may have reversed course and flown hundreds of kilometres in the wrong direction.
"There are issues about the quality of this information," said Steven Wallace, former director of the Office of Accident Investigation at the Federal Aviation Administration, when asked if the turnaround scenario was plausible.
"That question is very much on the table," he said. "What's the quality of this data?"
Uncertainty about the military's claim may explain why the search for the plane continued Wednesday in waters off both sides of the Malaysian peninsula. The chief of Malaysia's air force denied early reports attributed to him that military radar showed the China-bound plane turning back, but said he had "not ruled out the possibility of an air turn-back".
''I am not saying it's Flight MH370. We are still corroborating this,'' said General Rodzali Daud.
The radar used to track the flight after its transponder went dark Saturday morning was no more sophisticated than that used almost 75 years ago by London's defenders during the Battle of Britain.
It sends radio waves into the sky. When those waves encounter something, they bounce back. If the object happens to be the metal skin of an aircraft, it registers as a blob moving across the radar screen.
At the time Flight 370's transponder stopped functioning, the plane was at the outer range of Malaysia's radar. Radar is a line-of-sight instrument that can't look over the horizon, so its reach depends on the altitude of the airplane and on whether the radar equipment is located at ground level or on a mountaintop.
When a transponder is turned on — as is required on all commercial aircraft — it sends a signal to air-traffic controllers that reports the plane's speed, direction, altitude and call sign — in this case, MH370.
Because jetliners file flight plans in advance, a controller can check paperwork to confirm the type of plane — in this case, a Boeing 777.
If the transponder is turned off or suffers an electrical problem, the plane becomes no more than a moving blob on the screen, like a German Stuka dive bomber approaching London.
Air-traffic controllers have access to traditional radar, but they focus on transponder signals, which are referred to as secondary systems.
"The important distinction is that what 99.9 percent of air traffic controllers see is the secondary radar, which means that the controller is seeing information sent by the transponder of the airplane," Wallace said.
"Primary radar is what you need to have if you're trying to see someone who doesn't want you to see them, like an enemy attacking you," he said. "So primary radar is just looking at the reflection of the radar beam off the skin of the airplane, and it's of lesser quality; it doesn't provide any data."
The Malaysian military said that after Flight 370's transponder stopped transmitting, an unidentified airplane was detected at an altitude used only by airliners and military jets.
"That would not happen at high altitude unless it was military," Wallace said. "There wouldn't be any legal civilian operation without a transponder."
Wallace, who has spent decades investigating air crashes, ticked off notable cases in which an airplane has gone off course.
"Korean Airlines 007 in 1983, due to crew error, went off course into Soviet airspace and was shot down," he said. "Crew error is highly unlikely here. This was a way more modern airplane that has a GPS flight management system."
In two cases — involving EgyptAir in 1999 and SilkAir in 1997 — a suicidal pilot was thought to have brought the planes down, he said.
"I'm not suggesting that that was the case here," he said. "What happened here, if you believe this information [from the Malaysian military], was that the changing of course appeared to happen pretty much concurrently with the loss of the transponder. That has to suggest that control of the airplane was taken over by someone unauthorised."