A buoy dropped from a plane and equipped with a sensitive underwater microphone has recorded another promising signal

Flight MH370: Sonobuoy spots new signal as UK ship joins search

Another signal believed to be that of a black box of the lost Malaysian aircraft has been captured by a sonobuoy raising hopes MH370 might be found.

Planes have been dropping buoys with hydrophone listening devices attached to them at the end of a 300-metre long cable in the same area where Australian ship Ocean Shield recorded several signals in the past days.

The signal will have to be analysed to confirm it was manmade. However, the investigators are hopeful it could present the fifth instance of intercepting what is believed might be the MH370 flight data recorder beacons.

Following the detection of four signals by the towed pinger locator dragged behind the Ocean Shield, ships and planes hunting for signs of the lost MH370 focused on a 1,300 square kilometre area about 2,300km northwest of Perth.

In the meantime, it has been announced British survey ship HMS Echo has reached the region to assist Ocean Shield with the search.

The hydrographic sonar equipment carried by HMS Echo has been specially adapted to listen to pings transmitted on the 37.5 kHz frequency used by the black box beacons. The vessel was on a patrol in the Indian Ocean when asked by Malaysian authorities to help with the hunt and has already scanned the zone were a Chinese ship reportedly detected a similar signal on 5 April.

"My engineers worked incredibly hard to ensure the main engines and electrical propulsion drives have been running at full power, in order to reach the search area in the shortest possible time,” said Engineering Officer Lieutenant Andy Thomas.

"At the same time, we checked and maintained the survey equipment held on board to allow us the best possible chance to find the aircraft flight data recorder.”

Despite the recent positive news, investigators are aware the time to refine the search area is running out as batteries of the flight data recorder beacons have already reached their designed life time, meaning every new ping intercepted is a bonus. Experts have warned the beacons will likely cease operating within ten days. 

The investigators want to use the signals to narrow down the search zone even more before deploying an unmanned submarine to carry out detailed mapping of the seabed, which might be in the depth of up to 6km.

The US Bluefin 21 autonomous submarine which is ready to be deployed in the search takes six times longer to cover the same area as the pinger locator, and it would take the vehicle about six weeks to two months to canvass the current underwater search zone, which is about the size of Los Angeles.

According to analysis, the pings intercepted by Ocean Shield came from the depth of 4,5km, which is about as deep as the US Bluefin-21 autonomous underwater vehicle can get.

"It'll be pretty close to its operating limit. It's got a safety margin of error and if they think it's warranted, then they push it a little bit," said Stefan Williams, a Professor of marine robotics at Sydney University.

In case the wreckage is even deeper, another drone would have to be deployed.

However, Professor Williams said it was unlikely that the wreck had fallen into the narrow 5.8km deep Diamantina trench, since sounds emanating from that depth would probably not have been detected by the pinger locator.

Further teams are searching for signs of debris in the surrounding ocean.

Apart from HMS Echo, British nuclear submarine HMS Tireless is also working as part of the coordinated international team, using its sonar instruments to listen for the black box signal.

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