MH370 challenges remain in race for black box despite ‘encouraging’ acoustic clues

mr_012-1Reports over the weekend that the Chinese patrol ship Haixun 01 had detected possible signals from the black boxes of the missing Malaysia Airlines Flight 370 sounds were leapt on by news networks hungry for any details which could eventually lead to unravelling the mystery of why a modern aircraft could so suddenly and catastrophically disappear.

Media images of Haixun 01 sailors using hand-held sonar to look for the data recorder pinger have struck experts in the highly specialised field of sonar detection as absurd, however.

MH370 Search Briefing Q & A: April 7

The Benthos Diver Pinger equipment they were apparently using is designed for local searches for divers in shallow, sheltered waters, such as harbours, hardly the tool for the job in the very deep waters of the southern Indian Ocean. The listening device is designed to identify sounds at depths of less than 1,000 feet, while the ocean bottom in parts of the search area exceeds 14,000 feet. It was also reported that the Chinese did not make any recording of what they heard – explained possibly by the fact that recording is not a capability of the Benthos Diver Pinger.

Steve Winter is an international aviation consultant, technologist and a former naval consultant who has worked with the British Royal Navy to develop both new sonar technologies and the modelling of oceanic sound propagation, detection, and tracking. He says the idea of attempting to use such equipment on the open ocean, let alone for a wide-area search, is farcical.

“The Chinese military are under tremendous pressure from their government to solve this mystery, so they need to be able to show that they are doing something, anything, and making progress. This pressure will have percolated down through the military structure and caused these pictures to be released,” he tells Air Traffic Management.

Meanwhile, 300 nautical miles away the Australian Navy ship HMAS Ocean Shield equipped with a Towed Locator supplied by the US Navy looks to be conducting far more promising searches. Yesterday, those leading the Australian-led search effort announced that a detected sonar signal continued for two hours and 20 minutes with a second lasting for 13 minutes. On the second occasion two distinct ping returns were audible, something which was deemed to be the most promising lead yet. A slight variation in frequency between the two sonar signals could be explained because the pingers of the two recorders aren’t precisely the same age and their acoustic signals could vary slightly as a result.

“Detection with the Towed Pinger Locator (TLP) is a completely different matter to that with the hand-held device. The TLP is a purpose-built detector, which is towed deep underwater to provide maximum detection range of any pinger signals,” says Winter.

Even so, detecting the signal from the data recorder pinger will be highly difficult, even if HMAS Ocean Shield gets close to it.

“The ocean is a very noisy place,” he says, “and there are many noise sources that can be mistaken for the pinger. Steady contact with proper equipment over a significant period of time is the only way to detect it.”

The search effort will need to fix on a precise location before sending an underwater vehicle to investigate the finding, in an area of ocean whose depths are at the absolute limit of the unmanned underwater vehicle aboard Ocean Shield.

Also, a phenomenon in the ocean, known as the thermocline, which acts as a horizontal acoustic mirror below the surface makes it difficult for sound to propagate from the deeper reaches of the ocean. “That means that to detect pings from deep objects, you need to get below this layer, as the TPL is designed to do,” says Winter.

Winter believes there is cause for some optimism in the fact that on a second run HMAS Ocean Shield detected two signals – possibly one from each of the recorders. Winter here insists that the 30-day lifespan of the pinger is not deterministic and that it depends on the specific performance of the battery under the conditions and will tend to degrade over time past the 30-day mark.

“The 30-days is really just a performance guarantee under normal conditions,” he says. “It is, unfortunately, very unlikely that they will detect the pinger before its signal fades presuming it is even working. A full wide-area search over many months, using advanced autonomous underwater vehicles is the only realistic way to find the plane.”

Read:
Australian navy ship detects ‘promising’ underwater signals
MH370 search enters Day 30, detects two signal sources
MH370: Signals still to be verified, but characteristics ‘consistent’ with black box

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One Response to MH370 challenges remain in race for black box despite ‘encouraging’ acoustic clues

  1. Alfredo Walter Nuñez Gonzalez says:

    La caja negra de una aeronave así este demasiado averiado continua emitiendo señales de identificación
    esperemos que se logre su ubicación