Recovery teams on Sunday found the flight data recorder, which is the second black box, from the wreckage of the China Eastern Airlines Boeing 737-800 jet that crashed into a mountainside in southern China, according to state media.

The second black box was dug out of a slope at the crash site in muddy conditions after rain in recent days. The device had sunk 5 feet beneath the surface of the slope due to the impact. It will now be taken to Beijing for analysis of the, state media reports said.

This second black box contains crucial information about control settings, air data and other technological parameters related to mechanical issues of the plane that may have caused the crash.

Meanwhile, authorities have sent the cockpit recorder found at the crash site on Wednesday to a lab in Beijing for decoding. The black box was damaged by the impact of the crash, but the data inside appeared stable, officials said.

Two main theories that have now emerged about why the Chinese airliner suddenly nose-dived from a cruising height of 29,000 ft and crashed into a hillside.  Experts say that it was either due to a mechanical failure or sabotage, according to a BBC report.

If the plane was deliberately crashed, the cockpit voice recorder will definitely give an indication of this. 

The flight with 132 people on board, was on its way from Kunming to Guangzhou on the coast on Monday when it suddenly nose-dived at about the time it should have started its descent for landing.

The United States has also been invited to take part in the investigation of the crash as it involves a Boeing 737-800 plane manufactured in America.

Also read:  Two theories emerge on Chinese plane crash: Sabotage or technical failure?