A flight over China in clear skies, followed by a nose dive

BEIJING — China Eastern Airlines Flight 5735 was 29,100 feet in clear afternoon skies over the hills of southern China, apparently ready for a soft landing in Guangzhou. The plane, a Boeing 737-800 NG, was only seven years old. One of China’s most experienced aviators was among the three pilots in the cockpit.

But then, at 2:20 p.m. on March 21, the plane went down.

Air traffic controllers made frantic calls that went unanswered. The pilots did not send any Mayday message. The plane fell over 20,000 feet in less than a minute, to 7,400 feet. Then he gained 1,200 feet in about 15 seconds, before a final plunge down a hill covered in groves of bamboo and banana trees. The plane was almost exactly vertical and approaching the speed of sound as it sank into the soft earth, with pieces of the plane sinking up to 60 feet into the mud. Two pieces of a wingtip landed seven miles away.

Investigators, including a seven-member team from the United States who arrived on Saturday, are trying to figure out what happened in the final minutes before the plane plunged headlong, killing all 132 people on board.

Every air accident investigation poses unique challenges. But this one, China’s worst air disaster in more than a decade, is even more mysterious because the plane was obliterated by the extraordinarily high speed of its impact, essentially at a 90 degree angle. When the search ended last week, rescuers said they had recovered 49,117 pieces of wreckage.

China also maintains an unusually tight grip on news, censoring online discussion and speculation and allowing only limited coverage of the disaster. Chinese authorities have closely guarded much of the information about the crash. The families of the victims were monitored to prevent them from speaking to journalists or organizing demonstrations. The names of the pilots were not officially released, although a Hong Kong state newspaper published them anyway.

Much depends on the data that can be retrieved from the aircraft cockpit voice recorder and data recorder. The so-called black boxes are designed to withstand crashes, but experts say the severe impact of this one may have damaged the loggers to the point that some data was lost. The flight data recorder ended up five feet underground and could only be extracted after firefighters removed a large tree root above it.

NTSB spokesman Peter Knudson said the US National Transportation Safety Board was helping China download information from the cockpit voice recorder at a lab in Washington.

Credit…CCTV, via Associated Press

The tragedy has raised questions about the country’s flight safety record in an important year for China’s top leader, Xi Jinping, who will seek a third term at a Communist Party congress. China Eastern and its subsidiaries have grounded 223 Boeing 737-800s for security checks, a third of their overall fleet. The Politburo Standing Committee, the country’s top governing body, said at a meeting chaired by Xi last week that officials should determine the cause of the accident as soon as possible.

Officials overseeing the search said they recovered some key components from the plane, including parts of the engines and landing gear. They were trying to recreate the plane’s flight path using data from air traffic control radars and examining possible clues about baggage and mail placed on the plane.

Officials pledged to release preliminary findings within 30 days of the crash, in line with timelines set by the Convention on International Civil Aviation, a global agreement. This agreement also provides for the participation of representatives of the aircraft manufacturer and the transport safety regulator of the aircraft manufacturer’s country of origin. The National Transportation Safety Board said on Monday that investigators from the United States were not required to go through the usual lengthy quarantine when they arrived in China on Saturday. Instead, the team was allowed to go straight to the crash site, with some restrictions on their movements.

State media reporting on the accident was limited. A division of Jinan Daily, a state-owned publication in a city 1,000 miles away, published interviews with a farmer near the crash site who described seeing black smoke coming from the plane and with another farmer who described seeing white smoke. A surveillance camera installed in a remote mine recorded the last seconds of the plane’s vertical descent. These images showed no smoke.

“Nothing really seems to make sense with this one,” said Peter Marosszeky, a semi-retired airline executive engineer and technical adviser to Boeing, who is now chief executive of Aerospace Developments, a research and development company in Sydney, Australia. The black smoke would suggest burning fuel while the white fumes could be leaking fuel, but eyewitness accounts are very often unreliable in accident investigations, he added.

Air accident experts typically study the details that emerge from an accident investigation to look for signs of an in-flight collision or explosion, mechanical problems, or a pilot’s suicide. Virtually all the planes crashed in the same place, reducing the chances that a terrorist attack or other high-altitude accident took place, experts said. No explosive residue was found on the debris, according to Zheng Xi, the fire chief of the Guangxi region, where the accident happened.

A farmer’s discovery of a piece of the plane seven miles west of the crash site first raised speculation between experts that the plane suffered some kind of in-flight breakup. But Chinese authorities later confirmed that the fragment plus a much smaller fragment found a mile away were pieces of one of the plane’s fins, which are wingtip extensions that produce lift additional. Air crash experts said it was no surprise that such lightweight parts could land far from the site.

“It’s a winglet, so it’s going to fly like a wind – it’s not going to fall like a piece of aluminum, it’s going to fly,” said John Goglia, a retired NTSB board member who worked on air accident investigations. the world for more than half a century.

Damage to a winglet or loss of a winglet would not cause big changes in a pilot’s ability to stay aloft, Goglia added. “It wouldn’t cause a nose dive, and it’s possible it broke off as the plane approached supersonic speeds” during its descent, he said.

Aviation Partners Boeing, a Boeing joint venture with a wingtip maker that makes winglets for the 737-800, declined to comment on the discovery of the winglet fragments.

Aviation experts, including Mr. Goglia, focused in particular on the vertical position of the aircraft at the time of impact. Commercial aircraft are designed such that their natural tendency is to stabilize in flight. Achieving true nose-down requires constant and extreme force on the horizontal stabilizers on either side of the aircraft’s tail, Marosszeky said.

Horizontal stabilizers control an aircraft’s pitch – whether the front of the aircraft tends to pitch up or down. The question for experts is whether the plane’s nose was dented because of a technical malfunction or because of a pilot’s decision.

Martin Craigs, president of Aerospace Forum Asia, a Hong Kong-based trade group for aircraft equipment suppliers, said that during the China Eastern crash, the plane’s ability to fly almost perfectly straight without hovering nor float, helped show that “this is clearly not a terrorist bomb”. But he did not rule out a deliberate crash.

He cited the 2015 crash of a Germanwings flight carrying 150 people as an example of pilot suicide. “Nothing should be ruled out – remember, we deliberately flew a plane into the Alps a few years ago.”

Amy Chang Chien and Li you contributed to the research.

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