The head of Australia's transport safety bureau has defended the fruitless hunt for missing Malaysia Airlines Flight MH370, saying he is confident that search teams are targeting the right area.
Satellite analysis in the days after the Boeing 777 went missing on March 8 with 239 people onboard placed the jet somewhere in a huge tract of the Indian Ocean stretching from near Indonesia south towards Antarctica.
But in a setback, the area believed to be the jet's most likely resting place based on the detection of acoustic "pings" was ruled out after an extensive underwater search.
Australia's Transport Safety Bureau chief commissioner Martin Dolan told AFP the source of the acoustic transmissions, thought to be man-made, was still a mystery on Thursday.
"To be frank, we don't know. We like to be the experts but sometimes we just don't know the answer," he said, refusing to speculate on whether they came from the Australian vessel hunting for signals from the aircraft's black boxes.
Dolan, whose organisation is playing a key role in the search effort, said the four signals detected in April were then the best lead in the hunt for the plane, which mysteriously diverted from its Kuala Lumpur to Beijing route.
"This was the best area to look at the time. We still don't have anything that confirms that it's the wrong place. But we will do our analysis and we will determine the best search area for the next phase."
Dolan said while experts were reassessing the satellite data that led the search to the southern Indian Ocean, the linear arc produced by analysis of this information still likely represented the plane's flight path.
"That arc is definite. We know that somewhere close to that very long arc is where the aircraft will be found," he said in an interview on Thursday.
The arc was produced by analysing satellite signalling messages, also referred to as "handshakes", between the ground station, the satellite and the aircraft's satellite communication system.
Dolan said experts believed the aircraft would be found near the area representing the last of these signals, thought to be have been sent when the plane ran out of fuel.
"The thing that we're absolutely confident of is somewhere on that long arc we will find the aircraft," he said.
"But because it's so long we have to be able to find a much smaller segment of the arc to concentrate our search and that's what our analysis is looking at defining.
"So we are reanalysing all the satellite data and aircraft performance information and everything else to define an area of up to 60,000 square kilometres, which is the most likely one for the location of the aircraft."
The next phase will focus on using the satellite data to confirm a search area, completing mapping of the sea floor and getting towable sonar and other equipment to carry out an intensive deep water search, which could take up to a year.
Dolan voiced confidence that investigators had been given all the information available, but said he could understand the anger of relatives still looking for answers almost three months after the plane went missing.
"We're conscious that people don't have a particular confidence in the analysis," he said. "We have a much higher confidence. But we are nevertheless doing a cross check to verify it."
Dolan said the search was considered unique because there was so little information to go on, likening it to a worst-case scenario for aviation safety authorities.
"In an organisation like mine you work out what's the worst thing that will ever happen and hope that it never does," he said.
"And Australia has been very good at managing the safety of aviation, but our worst case scenario is a widebody passenger aircraft in mid-ocean.
"We've actually got plans to deal with this sort of thing, we just hoped we would never have to use those plans for real."