A Boeing 737-800 crashed in China with 132 passengers. Here's what we know about the aircraft and its safety.

• A Boeing 737-800 crashed in China with 132 people on board.
• The aircraft is one of the most used planes in the world with nearly 700 in operation in the U.S.
• Experts believe a system failure or malfunction could have caused the crash.

A Chinese airplane with 123 passengers and nine crew members crashed on Monday in the southern province of Guangxi, and officials started conducting rescue effortsat the site of the downed aircraft. 

Data from the flight-tracking website FlightRadar24.com shows the China Eastern flight was traveling at around 30,000 feet with a cruising altitude speed of 523 mph before it suddenly dropped. 

A fire ignited following the crash near the city of Wuzhou in Teng county, but hundreds of firefighters and rescue were dispatched to the scene and the fire was extinguished, according to the state-run China Daily. However, the outlet also reported a village official with the surname Zhou said the plane had "completely disintegrated" and he did not see any remains.

Chinese President Xi Jinping called for an "all-out effort" in the rescue operations and for any potential safety hazards that could have caused the plane to crash to be investigated. 

The aircraft that crashed was a Boeing 737-800. While Boeing has come under fire previously for crashes, it was the company's Boeing 737 Max that generated some of the harshest criticism over safety concerns.

There are differences in the aircraft, and Aerovise aviation expert Josh Verde told USA TODAY the Boeing 737-800 is a "tremendously safe airplane." Most accidents involving the plane have been runway-related.

In 2010, an Ethiopian Airlines flight, operated by a Boeing 737-800, crashed into the Mediterranean Sea, resulting in 98 deaths.

Here's what we know about Boeing 737-800:

How it happened:China plane crash, with 132 aboard, had frightening descent before impact

Chinese airline crash: Search continues for 132 people on board Boeing 737 that crashed in southeast China

How many Boeing 737-800 planes are in use today?

The Boeing 737-800 has been in use for nearly 20 years, and Verde said they are one of the most common aircraft used around the world, primarily in the United States, Europe and Asia.

Southwest Airlines, the nation’s largest domestic carrier, flies Boeing 737s exclusively with 728 in its fleet at the end of 2021. That included 207 Boeing 737-800s with an average age of six years. 

American Airlines had 267 737-800s, while United had 141 and Delta had 77. In total, the four major U.S. airlines have nearly 700 of the planes in their fleets.

Verde estimates in the U.S., there are roughly around 200 Boeing 737-800s in the air at any given time. 

What's the difference between a Boeing 737-800 and a Boeing 737 Max?

The Boeing 737 Max was heavily criticized after two international planes crashed in 2018 and 2019, resulting in 346 deaths. The plane was grounded worldwide and wasn't allowed to fly until several changes were made and it got recertified by the Federal Aviation Administration, which it did in Dec. 2020.

The aircraft is used in the United States, but David Yu, a finance professor specializing in aviation at New York University in Shanghai, told The New York Times the planes are not back in service in mainland China yet.

Anthony Brickhouse, associate professor of applied aviation sciences at Embry-Riddle Aeronautical University, told USA TODAY the key difference is the Max is the newer version, the engine is located in a different spot and the Max is more fuel-efficient. 

"I would encourage people not to automatically connect the dots between what happened today and what happened back in 2018 and 2019" Brickhouse said. 

Is the Boeing 737-800 safe?

The 737-800, part of Boeing's next-generation family, has had some issues in recent years. In 2019, the FAA ordered the inspection of heavily used 737 NGs for cracks in wing supports, which found several planes had wing cracks. 

However, Verde said the planes "don't have any ongoing areas of concern" and have had long, safe track records, alluding to how many airline companies use them today. He added the Boeing 737 Max was the first time he had seen the company cause a massive public scare.

"They're tremendously safe airplanes, and so the public certainly shouldn't have any concerns about getting on board one," Verde said.

Brickhouse said it's normal for people to feel uncertain about flying after a passenger plane crashes, but said it is still a reliable and safe plane to travel on, and investigations into the crash will lead to any necessary changes being made. 

What could have caused the Chinese plane to crash?

Video taken of the flight showed the plane in a straight nosedive moments before its impact, something Verde said could indicate the flight crew lost control of the plane. He said the impact force of that happening is "tremendous," and there's no guarantee anything on the plane, including the black box, would survive.

"Systems problems or a failure of some type is typically the only time you would see a plane in that nose down dive of attitude when you're talking about an airliner," Verde said.

"The cause of the plane crash is still under investigation, and the company will actively cooperate with relevant investigations," the airline said in a statement Monday. "The company expresses its deep condolences to the passengers and crew members who died in the plane crash."

Brickhouse, a former student trainee at the National Transportation Safety Board, said one thing that caught his attention was the aircraft's sudden drop in altitude. The plane was around 30,000 feet before dropping to around 9,000 feet in under three minutes. 

"That's not your typical descent rate for an aircraft," he said. 

There is no timetable of when it will be known what caused the crash, but Brickhouse said investigators don't focus on one piece of evidence alone, and collected evidence and data will help piece together what caused the crash. 

Contributing: Ryan Miller, Dawn Gilbertson

Follow Jordan Mendoza on Twitter: @jordan_mendoza5.