The breakthrough in the search has assisted analysts to gain a picture of the likely final sequence for the aircraft, which is believed to have run out of fuel and then experienced a last jolt of power that triggered an incomplete satellite handshake before entering the water. A helicopter leaves the flight deck of HMAS Success as it searches for the missing plane. Credit:AFP In such a scenario, the plane would likely have glided and could have turned upside down - rather than plunging into the water. Retired Air Chief Marshal Angus Houston, who is co-ordinating the multinational search, said an Australian navy ship had detected two sets of pulse signals that sounded "just like an emergency locator beacon". The development was, he said, a "promising lead". The first set was heard on Saturday and lasted for two hours and 20 minutes. The Ocean Shield ship then lost contact with the "pings" but turned around and later heard further signals for 13 minutes. It has since lost contact again and was trying last night to relocate the signals.

Significantly, Mr Houston said, the second set included two distinct sounds that would be consistent with transmissions from separate pingers attached to the black box's flight data recorder and cockpit voice recorder. The new signals are not believed to be related to those detected by a Chinese ship about 555 km to the south. "In the search so far it is probably the best information that we have had," said Mr Houston. "We are encouraged that we are very close to where we need to be. I would want more confirmation before we say 'this is it'." Chris McLaughlin, from British satellite company Inmarsat, which helped to identify the route of the plane by analysing its satellite "handshakes", said the location of the new signals appeared to coincide with the likely site of the aircraft's final mysterious transmission at 00.19 GMT - eight minutes after its last regular hourly handshake. After Inmarsat discovered the half-handshake two weeks ago, it estimated a possible endpoint for the flight much further north than previously thought.

The analysis was then further refined by a team of international experts, who assessed that the plane was travelling faster than thought, burning up more fuel, and would have landed even further north along the same arc. Likening the sequence to a car spluttering as it runs out of fuel, Mr McLaughlin said: "The partial handshake would be the plane running out of fuel and faltering for a moment, so the system went off network and then briefly powered up and had communication with the network. The plane looked for a final communication before it went off - and that was it." According to Stephen Buzdygan, a former British Airways pilot who flew Boeing 777s, the plane would then have glided into the water and may have rolled on to its back because its engines would have shut down asymmetrically. "Without fuel, assuming the crew were unconscious and no one was flying the plane, it would glide," he said. "Engines have separate fuel supply, so the chances are it won't go in with the wings level. With no autopilot correction, it would slowly turn on its back and go down at an angle and the wings would be ripped off." Despite authorities believing they are close to finding the plane in the southern Indian Ocean, Hishammuddin Hussein, the Malaysian defence minister, insisted that he had not lost hope of finding survivors. "I have always said to the families miracles do happen," he said. Chen Zesheng, 63, whose cousin was on the plane, said his family was treating the latest developments with caution. "We are sort of getting used to this kind of new finding now," he said. The aircraft's black box pinger has passed the 30-day point at which its battery life is expected to end - although it could last a further two weeks. The aircraft and the 239 people on board disappeared on March 8.

Mr Houston said the area in the ocean where the plane is believed to be located is 4500 metres deep. An underwater autonomous vehicle would be dispatched to comb the ocean bed for possible wreckage but its depth limit is also 4500 metres. Loading "This is very deep water - we are right on the edge of capability," he said. Telegraph, UK