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Explained | Why did the China Eastern Airlines plane nosedive before crash?

Rescue workers at the site of the China Eastern Airlines Boeing 737-800 plane crash, in Wuzhou, Guangxi Zhuang Autonomous Region, China on March 24.

Rescue workers at the site of the China Eastern Airlines Boeing 737-800 plane crash, in Wuzhou, Guangxi Zhuang Autonomous Region, China on March 24. | Photo Credit: Reuters

The story so far: On March 21, a China Eastern Airlines Corporation flight (MU5735) on a domestic flight in China, from Kunming to Guangzhou, abruptly impacted the ground west of Guangzhou in a mountainous area. The aircraft had 123 passengers and nine crew on board. At a press briefing on March 23, the Civil Aviation Administration of China  (CAAC) said that one of the black boxes had been recovered but was “substantially damaged”. Suspected debris (a large metal strip) has also been found 10 km away from the crash spot, pointing to possible mid-air disintegration.

What happens to the black boxes?

A CAAC briefing has said that based on a preliminary assessment, the black box device recovered is the cockpit voice recorder and that the “recording material appeared to have survived the impact in relatively good shape”. It is being decoded in Beijing, according to a report.

A black box must be able to withstand many accident scenarios. A document by the German Federal Bureau of Aircraft Accident Investigation says that ‘these devices are tested for extreme conditions such as an impact with a concrete wall at 750 kilometres per hour; a static load of 2.25 tons for at least five minutes, a maximum temperature of 1,100 degree Celsius (2,012 degree Fahrenheit) for one hour and water pressure of depths of up to 6,000 metres or over 19,500 feet’.

An aviation expert says the data files must be decoded first, as graphs, to get a sense of what happened. There is even the use of “spectral analysis” in some cases allowing experts and investigators to pinpoint even faint alarms or the hint of an explosion.

The U.S. National Transportation Safety Board (NTSB) — invited by China — is to take part in the investigation, as a U.S.-made aircraft is involved.

An aviation expert says that public and media pressure can be intense given that this is an age where people want instant answers. He cautions that getting an idea of what might have happened could take days, preliminary reports could appear after some months, while a detailed investigation could take even a year or more.

What are the additional details about the flight?

Flight MU5735 had left Kunming at around 1.10 p.m. local time and was scheduled to land at Guangzhou a little after 3 p.m. Introduced into service in June 2015, the Boeing 737-800 aircraft with CFM56 engines had completed a little over 18,000 hours of flight. A report has quoted a CAAC official as saying that the air controllers had been in contact with the crew throughout the flight — the implication is that there was no emergency/distress call. Later, the crew did not respond to controller attempts to contact them, which could point to a catastrophic event having occurred.

The captain, who was employed in January 2018, had 6,709 hours flying experience, while the first and second officers had 31,769 hours and 556 hours, respectively. The third pilot was an observer to accumulate flight experience. CAAC has added that the aircraft was in an airworthy condition and had been maintained in requirement with regulations. It also added that the family life of the crew was “relatively harmonious”.

Images have also emerged — apparently caught on video security footage from a mining company, close to the crash area — which seem to suggest that the aircraft was plunging toward the earth.

However, it is the data from tracking sites that have sparked interest.

What does some of the data show?

New 3D data visualisation by a leading tracking website shows the aircraft had been cruising at about 29,100 ft (nearly 9,000 metres; in China, the flight levels are assigned in metres). It then went into a dive from 27,025 ft to 7,425 ft. There was a climb to 8,600 ft and then a second dive to 3,225 ft, at which point the tracking stops — in total, an event over two-and-half minutes. The dive rate has been calculated to be 157 metres a second.

Experts have called this extremely excessive and unusual. An expert says this could be to do with the plane’s tail. Or even sabotage.

In an email in response to queries by The Hindu, David Learmount, Consulting Editor, Flightglobal/DVV Media International Ltd. (also former Operations and Safety Editor, Flightglobal, and former Flying Instructor, Royal Air Force) said, “The plateauing may well have been an attempt at recovery by one pilot. But why did the attempt then reverse itself? Was it two or three pilots fighting for different outcomes,” is a point he makes.

He added, “Of course, until we have hard data, sabotage or major failure is possibly the cause.” Mr. Learmount also said that if one looked at the issue of upset recovery — dealt with later in this FAQ — one had to look at what caused the upset.

In response to another query by The Hindu, Dr. Hassan Shahidi, President and CEO, Flight Safety Foundation, U.S., said, “This accident is very perplexing. The 737-800 series has had an excellent safety record. There are more than 4,200 in operations around the world and more than 1,100 in China. The investigators will be looking into all aspects of this accident, including mechanical and structural. They will be looking into the maintenance history of this aircraft as well as pilot training.

“This is certainly an unusual accident. At the moment, it is difficult to imagine what might have caused this airplane to nosedive at great altitude. We won’t know the cause, until the investigators have done their work. The data from the recorders will be crucial to understanding what happened in the moments the aircraft began its rapid descent.”

What about the issue of upset recovery?

A senior commander who flies the Boeing 777 aircraft told The Hindu that the issue of upset recovery could also enter the equation.

A senior commander who flies the Airbus family of aircraft told The Hindu, “Yes, it does matter depending on whether it was some kind of upset or disorientation that caused this crash. Upset recovery training would help a pilot handle any unusual attitude by an aircraft either due to environmental factors, physical factors such as disorientation or instrumental factors such as unreliable airspeed (as seen in the Air France AF447 crash, of June 2009), etc. It would not be very relevant for cases involving severe structural or mechanical failure. There will need to be more data to figure out what caused the China crash,” he said.

Data on commercial aircraft accidents and fatalities show that loss of control in flight counts among the single biggest causes. It is in recognition of this that the aviation industry and its regulators — India included — have begun to focus on Upset Prevention and Recovery Training, or UPRT.

UPRT is a mixture of theory and flying training, teaching flight crew to avoid and recover from situations in which an aircraft unintentionally exceeds normal flight parameters.

In aviation, flight crew confront a variety of weather systems and issues, with thunderstorms, being rated as one of the most hazardous. Therefore, if crew are caught up in a thunderstorm, UPRT would teach them to be familiar with where the most significant threat could occur from. And also the best recovery techniques.

UPRT, says the Boeing senior commander, is most certainly needed for professional pilots.

A document on UPRT says that in an upset, there is an ecosystem of causes, which include ‘environmental, systems and system malfunctions, aerodynamic issues, pilot induced/human factor and/or their combinations of the above’. UPRT training covers all of these. And, in crew training, the stress is on prevention. Equipping flight crew to ‘resolve an upset condition, both technically and emotionally’ is the key training goal.

Preparing pilots not only for flying skills training but also ‘ingraining the circumstances and precursors’ that could cause an upset are what form the technical aspects of training. Unexpected mental shock, G forces, noises and even changes in environmental conditions can affect flight crew, in turn impacting their ability to make decisions and take action.

Across the world, pilots are equipped with varied levels of capabilities and technical knowledge. The quality and type of their flight training also differs. It only needs reiteration that UPRT needs to provide a critical level of training when it comes to dealing with the threats that upset conditions pose.


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Printable version | Mar 27, 2022 4:32:12 pm | https://www.thehindu.com/news/international/explained-why-did-the-china-eastern-airlines-plane-nosedive-before-crash/article65261959.ece