Teams searching for the missing flight MH370 are trying to narrow down the area of the probable crash using signals believed to be from the plane’s black boxes before deploying an underwater drone.
Virtually days before batteries of the plane’s flight data recorders are expected to expire, Australian ship Ocean Shield, equipped with a US towed pinger locator, managed to intercept several signals.
According to experts analysing the data, the nature of the signals is such they can’t have originated from natural sources, such as whales. The search teams are hopeful they might finally be on track to determine the fate of the Malaysian plane that vanished on 8 March en route from Kuala Lumpur to Beijing.
On 5 April, the signal was detected twice, with the first instance lasting for more than two hours. On Wednesday, Australian officials announced two new pings had been recorded on Tuesday.
Analysts will now use the data to determine the approximate area of the crash before sending out the US Bluefin-21 underwater vehicle, equipped with sophisticated sidescan sonar, to create a detailed acoustic map of the area. The vehicle was previously used in the search for a F-15 fighter jet which crashed off Japan last year.
Analysing the presumed black box signals, operators must separate a ping lasting just 9.3 milliseconds - a tenth of the blink of a human eye - and repeated every 1.08 seconds from the natural cacophony of the ocean, as well as disturbances from other search vessels.
"The ocean is a noisy place," said Mike Davis-Marks, former commander of a sister vessel to British hunter-killer submarine HMS Tireless which has been dispatched to assist in the search.
"There is noise from everything, whether it's the ambient noise of the weather on the surface, or marine life like whales or the snapping noise of shrimps, not to mention other sea transport and low-flying aircraft."
The pinger locator that intercepted the signal was used previously in the search for the Air France jet that crashed in the Atlantic in 2009. The device has been described as the most powerful tool of its kind.
However, as the Indian Ocean in the search area is up to 4,500 metres deep, plotting the location of the source of the signal is a challenging task. In the deep waters, the analysts have to figure out the vertical as well as horizontal angle of the incoming signal. They also have to put up with the limited range of the pinger as water inhibits propagation of the signal with a relatively high frequency of 37.5KHz.
Once the search area is scaled down, the Bluefin-21 will be sent down to map it in detail. In case signs of wreckage are spotted, the vehicle will try to capture a photograph. However, assembling the mosaic of thousands of high-definition photos in the undersea gloom can be a long and frustrating task.
On one occasion during the search for Air France's lost Flight AF447, in waters almost as deep as the southern Indian Ocean, a remote vehicle investigated signs of wreckage, only to find sea shells instead.
Despite the recent breakthrough, the chances of retrieving the MH370 wreckage remain limited. The search for the Air France jet took almost two years in total and was only completed after a cash crisis that saw investigators trade down to a cheaper ship and accept indirect contributions from Airbus and the airline.
The US Navy says it has not yet been asked to help with salvage, but experts say the Remora 6000, designed by naval contractor Phoenix International which lifted the black boxes, wreckage and bodies from AF447, remains one of the few options.
The unmanned vehicle was used to view the Titanic and recover a Turkish F-14 Tomcat fighter, a Japanese rocket and an Israeli submarine.
However, AF447 was found on a flat plain near a mountainous ridge. Given the Indian Ocean depth and terrain, any MH370 retrieval operation may be more difficult.