Flight 5735 crash in China: mechanical failure or human action?

On Monday March 21, China Eastern Airlines Flight 5735 took off from Kunming in western China for a flight to Guangzhou on the south coast. After takeoff, the aircraft climbed to a cruising altitude of 29,000 feet and leveled off, moving east. Just over an hour into the flight, the plane nosedived sharply and crashed into a muddy mountainous area after plummeting about five miles in a minute and a half.

Recovery teams at the scene confirmed that there were no survivors among the 123 passengers and nine crew members. The two flight recorders (“black boxes”) have been recovered and are being analyzed, but Chinese officials stress that it is too early to draw conclusions about the cause of this tragedy, which is the worst disaster in the world. air transport in China since 2010.

As a precaution, China has grounded more than 200 of its Boeing 737-800 jetliners for enhanced safety inspections. So far, no other country has taken similar action, although the Boeing 737-800 is apparently the most popular airliner in its size class in the world. One of the reasons may be that the circumstances of the accident do not seem to indicate any particular mechanical failure.

Many types of mechanical problems in aircraft give some kind of warning before they cause life-threatening conditions. For example, the software glitches that led to the crashes of two 737 MAX planes in 2019 were known to cause the plane to behave unexpectedly under certain conditions, but the manufacturer (incorrectly) assumed that the training would allow pilots to take appropriate action to counter the aircraft’s tendency to pitch up and stall.

The information we have so far on Flight 5735 shows no signs that anything was wrong until the moment the plane nosedived. Stranger still, despite repeated attempts by air traffic controllers to contact the pilots during the 90-second dive, no response was received. The lack of response would be understandable if an explosion or other violent rupture of the aircraft occurred in flight, but eyewitnesses and the crash scene testify that the aircraft was largely intact until hitting the ground except for a small piece found about 10km away which could have broken off during the dive. Investigators believe that the speed of the plane could have approached the speed of sound, which is beyond its design speed and could have broken small parts before the accident.

Although Chinese officials have not addressed the issue directly, one possibility that needs to be addressed is that one or more of the pilots deliberately crashed the plane. Although highly unlikely, such a thing has happened before.

In 2014, Malaysian Airlines Flight 370 disappeared over the Indian Ocean with 239 people on board, and despite two extensive searches, the plane was never found, although small pieces were washed ashore. various places. In a well-documented article by Atlantic, William Langewiesche argues for the idea that the pilot, Zaharie Ahmad Shah, somehow overcame the other crew members, depressurized the cabin to an altitude that would have killed everyone on board apart from from the oxygen-supplied cockpit, then let the plane crash into the ocean, possibly after committing suicide.

It is too early to draw firm conclusions from the preliminary data we have on Flight 5735 and we may have to wait some time before the official investigation produces results. Under United Nations rules, the country in which a plane crash occurs is responsible for investigating the crash, and although there are links to American investigative agencies because Boeing manufactured the plane, they must play a secondary role.

Information from cockpit voice recorders, if available, will be extremely helpful in determining what happened before and during the last minute and a half of the flight. Reports indicate that no conceivable malfunction of the autopilot systems would cause the aircraft to go into and persist into such an extreme nose-down attitude, which apparently can only be induced by manual pilot intervention.

This raises a more general question: should new aircraft have software that would make such actions impossible that would inevitably lead to the loss of the aircraft?

In discussions of how the MCAS system, which is mostly software, led to the crashes of two 737 MAX planes in 2019, it seemed like we had already gone too far in the direction of a robot taking over. a plane. In any case, all new airliners are “fly-by-wire” in the sense that the pilot’s manipulations of the controls go through software systems which then perform the actual movement of the control surfaces.

From this perspective, it simply becomes a matter of judgment on the part of the computer as to whether to let what the driver tells the computer to take precedence over what the computer knows is best for the plane, or at least what could cause the plane to crash.

Perhaps the rarity of a pilot going crazy is enough to allow us to place our ultimate trust in the person actually flying the plane and not in software that has probably not been tested under the conditions that arise. would apply if a rogue pilot was determined to crash the aircraft.

Moreover, a pilot smart enough to fly an aircraft safely is likely smart enough to outwit software designed to prevent him from doing so.

Either way, we’ll just have to wait for Chinese crash investigation officials to come to their considered conclusions about the causes of Flight 5735’s crash. In his article on the Malaysian Air crash, Langewiesche says that personal information important on the Shah driver have been removed. by crash investigators, who were reluctant to admit the possibility that one of their own pilots deliberately caused the crash, which officially still has no determined cause. Political considerations can be a factor in accident investigations, and if the Chinese investigation ends empty-handed, it may be because indicating the most likely cause would be politically embarrassing.

Politics aside, if mechanical failure was involved, it’s important to get to the bottom of it so that all other 737-800 users can avoid such disasters in the future.

This article was republished with permission from the author’s Engineering Ethics blog

Karl D. Stephan earned the BS in Engineering from the California Institute of Technology in 1976. After a year of graduate school at Cornell, he earned the Master of Engineering degree in 1977… More by Karl D. Stephan

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