SYDNEY - Australia on Thursday ruled out a large swathe of Indian Ocean as Flight MH370's final resting place after a lengthy underwater hunt, as a US Navy official queried whether the missing plane ever went there.
The Joint Agency Coordination Centre said that the search with a mini sub of an area where acoustic transmissions were detected in early April was now complete.
"The Joint Agency Coordination Centre can advise that no signs of aircraft debris have been found by the autonomous underwater vehicle since it joined the search effort," JACC said.
It added that the Australian Transport Safety Bureau had advised that "the area can now be discounted as the final resting place of MH370" in an outcome that will extend the agony of relatives who are desperate for closure.
Australian ship Ocean Shield, which is carrying the US Bluefin-21 sub, has now left the area after scouring 850 square kilometres (340 square miles) of sea bed for the jet that vanished flying from Kuala Lumpur to Beijing on March 8 carrying 239 people.
The end of the underwater mission came as the US Navy's deputy director of ocean engineering Michael Dean told CNN that the pings at the heart of the search were no longer believed to have come from the plane's black box.
He said that if they were from the on-board data or voice recorders they would have been found by now.
"Our best theory at this point is that (the pings were) likely some sound produced by the ship... or within the electronics of the towed pinger locator," Dean said.
"Always your fear any time you put electronic equipment in the water is that if any water gets in and grounds or shorts something out, that you could start producing sound." He said it was not possible to absolutely exclude that the pings came from the black boxes, but there was no evidence now to suggest they did.
A US Navy spokesman later said his comments were "speculative and premature".