What We Know About the Crash of China Eastern Airlines Flight 5735

China Eastern Airlines Flight 5735 was making a short trip between two cities in southern China on Monday, cruising at an altitude of more than 29,000 feet, when it began a violent plunge toward the earth. Residents in the area described hearing a boom, apparently from the plane crashing into a hillside, and then seeing smoke from the fires it had ignited.

More than 24 hours later, emergency crews had found no survivors among the 132 people who were on board, officials said. The chances of finding anyone alive appeared slim. “It was in fragments scattered all around,” Li Chenbin, a technician in the area told the China News Service. “I didn’t see anyone who lived through it.”

But workers continued to comb the hilly, rural area, also looking for the Boeing 737-800 jet’s flight recorders.

Many questions remain about what led up to the crash of Flight MU5735. Here’s a look at what we know so far:

The plane plummeted more than 20,000 feet in about a minute.

Flight MU5735 took off shortly after 1 p.m. on Monday and the first hour of its journey proceeded as normal, Zhu Tao, the director of aviation safety at the Civil Aviation Administration of China, said late Tuesday. The plane was cruising at about 29,000 feet around 2:17 p.m., but a few minutes later air traffic controllers noticed the aircraft had suddenly lost altitude.

The plane lost more than 20,000 feet in just over a minute, according to Flightradar24, a tracking platform.

Air traffic controllers immediately called the plane crew, Mr. Zhu said, but did not receive a reply after several attempts. By 2:23 p.m., the plane’s radar signal disappeared, he said, and it had crashed.

Mr. Zhu acknowledged that officials had uncovered little information so far.

“The aircraft was severely damaged in this accident, and the investigation is very difficult,” he said. “With the information currently available, it is still impossible to make a clear judgment on the cause of the accident.”

The plane’s sudden dive occurred near a point in the route where it would normally begin its initial descent, according to Flightradar24’s records. The 675-mile flight from Kunming, the capital of Yunnan Province in southwest China, to Guangzhou, a major city in the southeastern province of Guangdong, usually takes about two hours. It crashed in Teng County in the region of Guangxi.

It is relatively rare for a plane to crash while cruising or during its initial descent. While cruising takes up more than half of the time commercial planes spend in the air, only 13 percent of fatal accidents happen during this stage, according to a Boeing report on data from 2011 through 2020. Just 3 percent of fatal crashes occur during the initial descent.

The plane was a workhorse model with a history of reliable service.

The plane was a Boeing 737-800 that had flown for nearly seven years. It was not a 737 Max, the model that was grounded worldwide after two fatal crashes in 2018 and 2019 that were caused by a faulty flight stabilizing system.

The 737-800 is part of Boeing’s Next Generation series. It is a narrow-body model, with nearly 5,000 built since it first went into production in the late 1990s. The widely used model has a good safety record, with 22 hull-losses, meaning the plane was damaged beyond economical repair, recorded over the past two decades, according to the Aviation Safety Network database.

China Eastern has vastly improved its safety record.

China Eastern Airlines, the country’s second-largest carrier, had a checkered record in its early years, with multiple deadly crashes in the late 1980s and 1990s. In 1989, a China Eastern flight lost power after takeoff in Shanghai, killing 34. And in 1993, an error by a crew member forced an emergency landing in Alaska that killed two passengers.

In 2004, a buildup of ice on the wings of a China Eastern plane flying from Baotou in Inner Mongolia caused it to crash, killing 55. Since then, the airline’s safety record drastically improved, with no fatal crashes before Monday, according to flight safety databases.

The airline’s safety history mirrors that of China as a whole. In the 1990s the country was considered one of the most dangerous places in the world to fly. But after officials carried out a regulatory overhaul, the country has maintained an admirable safety record. The country’s last major crash before Monday was in 2010.

On Tuesday, a China Eastern official, Sun Shiying, said the aircraft and crew for Flight 5735 had met requirements before takeoff. He did not directly respond to questions about the plane’s maintenance history and the number of flight hours the pilot had accumulated.

The investigation is just beginning, but the cause could be complex.

The Civil Aviation Administration of China said on Monday that it activated an emergency mechanism as soon as it received reports of the crash and sent a team to the site to begin an investigation. The agency also said it would require “more industrywide efforts to improve aviation safety.”

Boeing, the plane’s manufacturer, said Monday that it was in contact with the U.S. National Transportation Safety Board about the crash, and the manufacturer’s technical experts were prepared to assist the Civil Aviation Administration of China in its investigation.

The initial investigation will focus on information from the flight data recorders, or black boxes, which have yet to be recovered. Experts will also study video records that have emerged, including security footage from a mining company that appeared to show a plane heading directly toward the earth.

Because airplanes are so technologically complex, the cause of a crash is always difficult to identify and always multilayered, experts said. Official reports on a crash’s cause can take months, or longer, to complete

“It’s never one thing,” said Thomas R. Anthony, the director of the aviation safety and security program at the University of Southern California. “There may be one thing that’s obvious, there may be one primary thing, but it’s never one thing.”