Sweep of ocean floor fails to find plane 'pings'

Search crews hunting for the missing Malaysia Airlines jet have failed to relocate faint sounds heard deep below the Indian Ocean said to have been consistent with a plane’s black boxes.

Angus Houston, the retired Australian air chief marshal who is heading the search operation far off Australia’s west coast, said sound locating equipment on board the Ocean Shield picked up no trace of the signals since they were first heard late on Saturday and early on Sunday.

Time is running out to find the devices, whose locator beacons have a battery life of about a month. Today marks exactly one month since the plane vanished.

“There have been no further contacts with any transmission and we need to continue that for several days right up to the point at which there’s absolutely no doubt that the batteries will have expired,” Mr Houston said.

He said the Ocean Shield crew may spend several more days towing sophisticated US Navy listening equipment deep within the ocean to try and find the sounds again. Only at that point, he said, would a sub on board the ship be sent below the surface to try and chart out any debris on the sea floor. If it maps out a debris field, the crew will replace the sonar system with a camera unit to photograph any wreckage.

Mr Houston’s comments contradicted an earlier statement from Australia’s acting prime minister Warren Truss, who said search crews would start the Bluefin 21 autonomous sub today.

At the weekend the towed pinger locator detected two distinct, long-lasting sounds underwater that are consistent with the pings from an aircraft’s “black boxes” – the flight data and cockpit voice recorders.

Mr Houston dubbed the find a promising lead in the month-long hunt for clues to the plane’s fate, but warned it could take days to determine whether the sounds were connected to Flight 370, which vanished March 8 on a flight from Kuala Lumpur, Malaysia, to Beijing.

Finding the black boxes is key to unravelling what happened to Flight 370, because they contain flight data and cockpit voice recordings that could explain why the plane veered so far off course.

The first sound picked up by the equipment on board the Ocean Shield lasted two hours and 20 minutes before it was lost, Mr Houston said. The ship then turned around and picked up a signal again – this time recording two distinct “pinger returns” that lasted 13 minutes.

“Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder,” he said.

The black boxes normally emit a frequency of 37.5 kilohertz and the signals picked up by the Ocean Shield were both 33.3 kilohertz, US Navy captain Mark Matthews said. But the manufacturer indicated the frequency of black boxes can drift in older equipment.

The frequency used by aircraft flight recorders was chosen because no other devices use it and nothing in the natural world mimics it, said William Waldock, a search-and-rescue expert who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Arizona.

But these signals are being detected by computer sweeps and “not so much a guy with headphones on listening to pings”, said US Navy spokesman Chris Johnson, so until the signals are fully analysed, it is too early to say what they are.

“We’ll hear lots of signals at different frequencies,” he said. “Marine mammals. Our own ship systems. Scientific equipment, fishing equipment, things like that. And then of course there are lots of ships operating in the area that are all radiating certain signals into the ocean.”

Geoff Dell, discipline leader of accident investigation at Central Queensland University in Australia, said it would be “coincidental in the extreme” for the sounds to have come from anything other than an aircraft’s flight recorder.

“If they have a got a legitimate signal and it’s not from one of the other vessels or something, you would have to say they are within a bull’s roar,” he said.

“There’s still a chance that it’s a spurious signal that’s coming from somewhere else and they are chasing a ghost, but it certainly is encouraging that they’ve found something to suggest they are in the right spot.”

The Ocean Shield is dragging a ping locator at a depth of 1.9 miles. It is designed to detect signals at a range of 1.12 miles, meaning it would need to be almost on top of the recorders to detect them if they were on the ocean floor, which is about 2.8 miles deep.

Mr Houston said the signals picked up by the Ocean Shield were stronger and lasted longer than faint signals a Chinese ship reported hearing about 345 miles south in the remote search zone off Australia’s west coast.

The British ship HMS Echo was using sophisticated sound-locating equipment to determine whether the two separate sounds heard by the Chinese patrol vessel Haixun 01 were related to Flight 370. The Haixun detected a brief “pulse signal” on Friday and a second signal on Saturday.

Meanwhile, the search for any trace of the plane on the ocean’s surface continued, with up to 14 planes and as many ships focusing on a single search area covering 29,954 square miles of ocean, 1,400 miles north west of the Australia’s west coast city of Perth.