A mystery underwater sound recorded at the time missing Malaysia Airlines flight MH370 vanished is being investigated by Australian researchers
Flight MH370
© Press Association/Associated PressFlight MH370 disappeared three months ago
The low-frequency noise was picked up by underwater listening devices in the Indian Ocean off the west coast of Australia on March 8, the same day that the stricken plane carrying 239 people disappeared.

Researchers are analysing the signal to determine whether it could be the noise of the jet crashing into the ocean.

Search teams have been working on the theory that the plane, which was meant to be heading to China, instead went south before crashing into a remote part of the Indian Ocean.

Despite extensive underwater searches of an area narrowed down by authorities, no sign of the missing Boeing 777 has been found.

Researcher Alec Duncan, of Curtin University in Western Australia, acknowledged that the sound being analysed by his team fell outside of the projected flight path officials believed the plane took.

He said: "It's one of these situations where you find yourself willing it all to fit together but it really doesn't.

"I'd love to be able to sit here and say, 'Yeah, we've found this thing and it's from the plane' - but the reality is, there's a lot of things that make noise in the ocean."

He said there was about a 20 per cent chance of the noise being linked to the missing plane, adding that it could have been caused by a natural event such as a small earthquake.

The International Air Transport Association has said that plans to improve global tracking will be ready in September, to make sure there is "no repeat" of the mystery surrounding the fate of flight MH370.