SYDNEY (WSJ): -The Australian navy renewed an underwater search for Malaysia Airlines 3786.KU 0.00% Flight 370 on Tuesday, focusing on a narrow area of the southern Indian Ocean where crews had earlier picked up signals consistent with those of black box flight recorders.
The naval ship Ocean Shield, which is fitted with U.S. Navy equipment able to pick up black box signals far beneath the ocean surface, was to scour the northern end of a search zone covering 77,580 square kilometers (29,954 square miles) off the coast of Western Australia. Investigators believe the area is the most likely spot where the plane may have run out of fuel, more than a thousand miles from the nearest airport, after disappearing from civilian radar on March 8.
Two other military ships from China and the U.K. were tasked with searching an area of ocean further to the south amid growing optimism among Australian authorities that they may be close to be a breakthrough in the monthlong search for Flight 370. The subsea effort was supported by an aerial search of the ocean surface for possible plane debris involving up to 14 aircraft and an equal number of ships.
It comes after Air Chief Marshal Angus Houston, who is leading the multinational search, said Monday that the Ocean Shield had detected separate series of signals on Saturday. The first was held for more than two hours. On a return trip along the same path some hours afterward, two distinct pinger signals were detected and held for about 13 minutes.
“Significantly, this would be consistent with transmission from both the flight data recorder and the cockpit voice recorder,” Air Chief Marshal Houston said. “Clearly this is a most promising lead…The audible signal sounds to me just like an emergency-locator beacon.”
So far, the multinational team of military aircraft has failed to spot any debris related to Flight 370 on the surface of the ocean in more than two weeks. Instead, investigators have relied on radar, satellite communications and other data to plot where they believe plane likely went down.
That analysis, which has been revised several times, steered the Australian-led search operation to direct the Ocean Shield to an area of ocean about 650 miles from the town of Exmouth on the western Australian coast.
Once on site, the Ocean Shield swept back and forth across a seven-mile strip of open sea, towing the black box detector equipment some 3,000 meters, or nearly 2 miles, beneath the surface. The highly sensitive equipment usually needs to come within about 2,000 meters of black boxes to register their pings, Australian Navy Commodore Peter Leavy said.
Sounds under the surface are affected by temperature, pressure and salinity, which can affect the quality and range of any underwater signals, he said.
Air Chief Marshal Houston said searchers still needed to fix on a precise location before sending an underwater vehicle to investigate the finding, in an area of ocean some 4,500 meters deep. Those depths are at the absolute limit of the undersea vehicle aboard the Ocean Shield, which might mean that crews would have to use other submersibles or drop cameras to the ocean floor to investigate.
Anish Patel, president of Dukane Seacom, the company which manufactures the beacon, says the pinger signals being picked up by Australia and China in the Indian Ocean could very well be coming from the black box of Flight 370.
Air Chief Marshal Houston’s announcement Monday came at a critical time in the search. Locator beacons on the two flight recorders aboard the plane have an estimated battery life of 30 days before they stop emitting signals.
In a hunt that has been fraught with false leads and setbacks, authorities were careful to inject some caution.
“In deep water, funny things happen with acoustic signals,” Air Chief Marshal Houston said. “I would not be prepared to confirm that this is the spot where the aircraft is on the present evidence,” he said. “Without wreckage, we can’t say it’s definitely here. We have to go down and look.”
Air-safety experts have said other maritime locating devices use similar frequencies to flight recorders. Following a signal that search teams detected on April 3 but later discounted, the Australian agency leading the search operation warned that biological sources, such as whales, could lead to false alerts.
Commander William Marks, a spokesman for the U.S. Navy’s Seventh Fleet, said the Ocean Shield picked up returns with a slight variation in frequency. He said that could be explained because the pingers for the two recorders aren’t precisely the same age and their acoustic signals could vary slightly as a result.
The Ocean Shield was searching at the northern end of an arc determined as the most likely flight path for the missing Boeing 777, based on updated satellite and aircraft performance data, when it made the discovery. Friday and Saturday, a Chinese vessel, Haixun 01, reported detecting several “acoustic pings” 1.2 miles apart—about 300 nautical miles from the Australian naval ship on the edge of the southernmost of three designated search zones.
The Chinese listening device was designed to identify sounds at depths of less than 1,000 feet, according to one person briefed on the Flight 370 probe, while the ocean bottom in parts of the search area exceeds 13,000 feet (2.5 miles).
Still, Air Chief Marshal Houston said Monday the Australian finding doesn’t rule out the earlier Chinese discovery. If the plane flew at a slightly slower speed than would be normal with better fuel conservation, it would likely have hit the water near the Chinese vessel. If it flew somewhat faster and burned more fuel, it likely would have crashed into the ocean nearer to the Ocean Shield location. U.K. Navy ship HMS Echo was on its way to assist the Chinese vessel in its search on Monday.
The former Australian defense chief warned that even if searchers can recover the signal again and accurately pinpoint the wreckage, they are in for a long recovery effort with the Southern Hemisphere winter fast approaching.
“We’re talking about a long operation here that will be measured in months,” Air Chief Marshal Houston said. “It will take several days to actually cover what would appear to be a fairly small area. Things happen very slowly at the depths we are dealing with,” he said. “Some of the water out there exceeds 5,000 meters, which is going to be very challenging.”