KUALA LUMPUR (THE STAR/ASIA NEWS NETWORK) - Malaysia Airlines Flight MH370's cockpit voice recorder will not yield any answers about the critical moment the plane deviated from its Beijing-bound route as the voice data have been erased due to the recorder's two-hour recording cycle.

This means that investigators might never fully solve the mystery of MH370 as it would be impossible to know what went on in the cockpit after air traffic control lost contact with the aircraft at the border of Malaysia-Vietnam airspace.

A source familiar with the workings of the "black box", comprising the cockpit voice recorder (CVR) and flight data recorder (FDR), said technical information from the FDR alone would not be enough if investigators found that mechanical error was not the problem.

"Trained specialists would be able to gain a lot of information from the Flight Data Recorder. But if it wasn't mechanical error but deliberate action? I think we will not be able to tell what really happened without the voice data," he said.

According to US firm Honeywell Aerospace which supplied the black box, only the last two hours of recording are maintained as the recorder continuously records over itself throughout the flight.

"The principle is in place because it is normally the last section of a flight that determines the cause of the crash," reported the BBC.

The exhaustive search and rescue operation to locate MH370, deemed to have ended in the southern Indian Ocean, looks set to become even harder if the recorders are not found before the two beacons run out of battery life in about two weeks.

Although the US Navy's Towed Pinger Locator 25 (TPL-25) arrived in Perth on Thursday, authorities have yet to identify whether the debris spotted by satellite is even connected to MH370.

Britain's The Telegraph quoted aviation specialist David Barry as saying that the "pings" from the beacons could continue for an extra 10 days.

"Given the remoteness of the site and the depth of the water and the weather down there, the black box will be almost impossible to find.

"It will then be a case of digging through the wreckage field, possibly for a couple of years," he said.