Investigators in China Thursday say the search continues at the mountain-side crash site for the data recorder from a Chinese airliner that went down Monday in southern Guangxi province.

Meanwhile, officials with the Civil Aviation Administration of China said, while the outside casing of the cockpit voice recorder — the first of the two so-called “black boxes” from the flight recovered Wednesday — was damaged, its contents are in good shape and investigators have begun examining them.

The voice recorder contains audio in the cockpit between members of the flight crew as well as communications with ground crews. The data recorder preserves information on the plane’s performance including airspeed, altitude, system performance and direction.

China Eastern Flight MU5735 went into a sudden dive and slammed into a mountain outside the city of Wuzhou. The Boeing 737-800 jetliner was carrying 132 passengers and crew on a flight from Kunming in Yunnan province to the industrial city of Guangzhou.

Data obtained from flight tracking website FlightRadar24 showed Flight MU5735 plunged at a rate of nearly 8,870 meters per minute before it crashed.

So far, pieces of the plane and human remains have been found, but no survivors, though officials have yet to officially declare anyone dead.

Officials have said the search for the plane’s flight data recorder and additional wreckage has been hampered by heavy rain, and the large crater caused by the crash was filling with water, raising the risk of small landslides on the steep slopes.

The crash has prompted China Eastern to ground its entire fleet of Boeing 737-800 planes. China’s civil aviation regulator has announced a two-week safety inspection across the industry.

Monday’s crash was the worst for China’s aviation sector since 2010, when a Brazilian-built Embraer passenger jet operated by Henan Airlines crashed as it was landing in the northeastern city of Yichun, killing 42 of the 96 people on board.