Four weeks after a Malaysia jetliner headed to Beijing went missing, time is running out for the flight data recorders' pulse signaling system, as their batteries are expected to give out any day.
So-called black boxes are designed to emit sonic pings for roughly 30 days to aid searchers. Malaysia Airlines Flight 370 disappeared on March 8.
The Chinese news agency Xinhua on Saturday said a black box detector deployed by a Chinese ship, Haixun 01, heard a signal at 37.5 kilohertz, which is set aside for the black-box pinger as other underwater sounds typically aren't emitted at that frequency.
On Sunday, the Australian official coordinating the search said the Haixun 01 had detected two sets of signals and an Australian ship was investigating another "acoustic event" on Sunday.
William Waldock, an expert in aviation accident investigation at Embry-Riddle Aeronautical University in Prescott, Ariz., said it’s possible for other sources — for example, a passing submarine — to transmit in frequencies close to 37.5 kHz. The one-second pulse from a pinger, however, is “a very distinctive pattern.”
“If it’s verified, it’s a major break in the case,” he told NBC News. “Frankly, they got lucky.”
He said the spotty nature of the transmission would make sense, because the Chinese ship was probably sailing through the edge of the reception area. Pingers are designed to be detected within a four-mile radius. Picking up the intermittent signal is expected to spark a more concentrated, more methodical search — not only by the Chinese, but by other ships from the international armada in the area.
If the detection is confirmed, it’s not only a stroke of luck for the location, but for the time frame as well. The battery-powered pinger is designed to operate for 30 days — a block of time that expires in just a few days. Waldock said the batteries could keep going for some time afterward, but the signal would “become fainter and fainter.”
The data recorder typically holds up to 25 hours’ worth of data about the plane’s performance, including speed, altitude, flight control and engine parameters. The voice recorder documents the last two hours of conversation in the cockpit.
The recorders can survive salt water immersion up to 20,000 feet and the data can be preserved for two years or longer — although the lack of a pinging system makes finding the boxes more difficult.
Confirming the signal picked up by the Chinese ship is just the start.
“If we’ve found the haystack, now we’ve got to find the needle,” Waldock said.
One option would be to drop sonobuoys from the P-3 Orion surveillance planes that have been participating the search. These devices are expendable sonar stations, contained in 3-foot-long, 5-inch-diameter canisters. The buoys can send back readings to help searchers triangulate on the black box’s location.
Another option is to survey the seafloor with autonomous vehicles equipped with sonar equipment.
Once a wreckage field is located, searchers could send down camera-equipped, remotely operated underwater robots to look for the black box and bring it up.
Malaysia is in charge of the investigation, but Waldock said Malaysian authorities probably “don’t have the laboratory capability” to deal with analyzing the data from the flight data recorder and the cockpit voice recorder. The black box could be flown to a lab in a different country — Australia, for example — for detailed analysis.
Waldock said he was among the experts who were starting to think the mystery of Malaysia Airlines Flight 370 would never be solved. For a parallel, he reached back to the case of famed aviator Amelia Earhart, who disappeared in the Pacific during her attempt to fly around the world in 1937.
“If it’s confirmed, this is right up there with finding Amelia Earhart,” Waldock said.