Aviation experts say the plane that crashed in the South China mountains on Monday was one of the safest in the world, raising questions about the Boeing 737-800 NG, one of the industry’s workhorses.

The fate of China Eastern Airlines Flight 5735’s 132 passengers and crew members is unknown after the plane crashed in the mountains of southern China. Flight recordings and the final minutes of air traffic control communication are likely to be used by investigators to figure out what caused the crash.

During a flight between Kunming and Guangzhou in China’s south, the plane lost contact over Wuzhou, according to the airline and the country’s Civil Aviation Administration. The investigation is being led by the latter.

“They’ll be looking for the flight data recorder and the voice data recorder from the crash site because they contain crucial information about what happened in the final moments before the plane plummeted to the ground.” That will be critical,” Hassan Shahidi, president of the Flight Safety Foundation, a non-profit that promotes aviation safety, said.

Investigators will also look into the aircraft’s and engine’s maintenance history, the flight crew’s recent training, and the pilot’s experience, he said.

Investigators will also want to know about the pilot’s communications with air traffic control in the minutes leading up to the crash, according to Shahidi.

The 737-800 NG, or Next Generation, was considered one of the safest aircraft in the world before the crash on Monday. According to the aviation consultancy Cirium, the fleet has only had 11 fatal accidents out of more than 7,000 planes delivered since 1997.

According to the group, more than 4,200 planes are in passenger service, accounting for about 17% of the global fleet. There are 1,177 of them in China. The planes are operated by all four major US carriers, according to Cirium.

The 737-800 NG appears to have a better recent safety record than the Boeing 737 Max 8, which was banned from the skies worldwide in March 2019 after two crashes killed more than 300 people.

In October 2018, Lion Air Flight 610 crashed in Indonesia, killing 189 people. Five months later, Ethiopian Airlines Flight 302 crashed shortly after takeoff, killing all 157 people on board.

In December 2020, a new version of the plane made its first commercial flight in the United States.

The accident on Monday may rekindle those safety concerns. Representatives from Boeing, the Federal Aviation Administration, and the plane’s engine maker, CFM, will serve as technical advisers, according to the National Transportation Safety Board, which has appointed a senior air safety investigator to represent the United States in the investigation.

Boeing issued a statement saying, “Our thoughts are with the passengers and crew of China Eastern Airlines Flight MU 5735.” “We’re collaborating with our airline customer and are prepared to assist them.”

According to data from the flight-tracking website FlightRadar24, the flight left Kunming at 1:11 p.m. (1:11 a.m. ET) and arrived less than two hours later. It revealed that the plane rapidly lost altitude while cruising just over an hour into the flight, descending from 29,000 feet to its last tracked position in a matter of minutes.

According to Willie L. Brown Jr., a pilot and associate professor of aviation at the University of Maryland Eastern Shore, the pilot was no longer in control because the plane dropped so quickly.

Investigators will try to figure out what role, if any, the weather and the mountainous region played in the plane’s history, according to Brown. “In general, I’d try to figure out what the aircraft’s structural integrity was,” Brown said. “Anything could happen.”

Experts predict that determining what caused the plane to crash will take some time.

“It’s really too early at this point,” Shahidi said. “There are a number of things that could have gone wrong, but data and information are the only way to figure it out.”