MH370: Has China Cracked 'Mission Impossible'?

Experts say Chinese search crews will have overcome an "impossible situation" if they recover the black box from the missing Malaysia Airlines plane.

Chinese state media claims a signal has been discovered by the country's Haixun 01 vessel 1,000 miles northwest of Perth.

The signal is said to have a frequency of 37.5kHz per second - the same as that emitted by black-box devices.

Oceanographer Dr Simon Boxall, from Southampton University, told Sky News it would be a remarkable achievement.

"If it proves this is potentially from the pinger on the black box then we've gone from pretty much an impossible situation to locate this flight and the wreckage on the seabed to a situation where it's very feasible," he said.

"It would mean we've gone from an area of 85,000 square miles down to an area of 10 square miles.

"Because the signal is so weak on this locator, it can't be more than two or three miles away.

"Even if the seabed is fairly mountainous or there are issues on the sea floor, it's within the capability of 21st century technology to recover this black box if the signal proves to be from the aircraft.

"The search area would be doable but it could take months."

Dr Boxall says the next step is to confirm the signal is from MH370.

This would be done using a combination of side scan sonar and camera equipment attached to an ROV (remotely operated underwater vehicle).

If they confirm the presence of a black box, the operation will enter its recovery phase.

This could be hampered by weather, with relatively calm seas required for a whole day to allow the ROV to reach the seabed.

"You shouldn't underestimate the size of this task - it's not easy," said Dr Boxall.

A map showing the spot where the plane's ping was located

The location of objects spotted in the southern corridor

"But you go to something that will happen, rather than something that may never happen.

"Possibly when they do that some of the mysteries of what happened to MH370 might be answered."

Another question is which country will lead any verification and recovery, as the signal has been found in international waters.

But Dr Boxall warns there is a long way to go before this becomes an issue.

"Without showing scepticism, it's interesting that this has happened four weeks after the event and it's happened at the point when people are saying, incorrectly, that the black box is going to run out in two hours," he said.

"The black box has a design transition of about 30 days. It could go on for longer, it could have been damaged in the crash itself.

"The ocean is full of noise. Both equipment we use as scientists or natural noises.

"The argument is that there's nothing else out there that will transit at 37.5kHz but we also know the signal was very intermittent, which we would sort of expect - but how intermittent?

"Because this is all second-hand information, then until this data has been looked at by the Australians, I'm afraid to say my scepticism will remain."