Back in March, we blogged about the crash of China Eastern Airlines Flight 5735, which crashed on March 21 during a flight from Kunming to Guangzhou, killing all 132 people on board. At the time, it was too early to draw any conclusions, as the investigations had just begun and the flight data recorders had not yet been recovered. Within days, however, the voice and data recorders were found, and the data recorders were sent to the US National Transportation Safety Board (NTSB) for analysis.

In April, rumours began to circulate in China that the crash was caused deliberately by someone on the flight deck. These rumours were substantiated when several US news outlets, including the Wall Street Journal and ABC News, reported in May that US officials had determined that someone in the cockpit had pushed the control stick forward to initiate the dive from 29,000 feet that led to the crash. The Civil Aviation Administration of China (CAAC) has neither confirmed nor denied these reports, while grumbling that “unofficial speculation” can interfere with the ongoing investigation. Nevertheless, until further official information is made available, it looks like deliberate action on the part of someone in the cockpit may well have caused the crash.

The Wikipedia article on the crash lists the three members of the flight crew: Captain Yang Hongda, who had been a Boeing 737 pilot since 2018; First Officer Zhang Zhengping, an award-winning commercial pilot with more than a decade of experience, including the training of 100 other pilots; and Ni Gongtao, a trainee with less than 600 hours of flight experience whose official duties were simply to observe the more experienced pilots.

The psychology of a flight crew is a somewhat neglected but vital aspect of the smooth functioning of the team, who must cooperate effectively under both routine and emergency conditions. Any time there is more than one person involved in a situation, there will be questions of authority and precedence. That is why the very titles of the flight crew indicate a precedence of authority, the captain being in charge of both first and second officers.

An excessively rigorous adherence to the priorities of rank can be detrimental, as the 1997 crash of Korean Air Flight 801 illustrates. Despite errors the captain of that flight made in his approach to the Guam airport, he was not challenged by the other two members of the flight crew until six seconds before the crash, by which time it was far too late to do anything. Since that time, Korean Air and other flight organizations have emphasized that the authority of the captain is not absolute, and if the other members of the flight crew see that the captain has made a mistake, they should take positive action to correct it.

But in the case of Flight 5735, it would be hard to believe that deliberate action to crash the plane would be taken by more than one of the three flight-crew members. If we assume that only one of the three men on the flight deck decided to crash the plane, that raises several hard questions.

First, one would think that two men determined to save themselves and the passengers could overpower one man bent on destroying the plane. While I have no details of how a 737 cockpit is arranged, it’s hard to imagine a way that one man could impose his will on the others and remain at the controls, if the other two were determined to stop him.

As long as we’re imagining things, suppose the suicide pilot, let’s call him, somehow smuggled a firearm along with him, and threatened to shoot anyone who interfered with him? That would be awkward, but conceivable. And it’s not clear whether pilots go through the same security checks that passengers do, and if they do, how easy it would be to evade them in order to carry a gun on board.

Neither of those scenarios seem too credible. An interesting fact from the record of the flight before the crash is that it briefly levelled off around 8,000 feet before continuing its plunge into the mountains. This might indicate a temporary turn for the better in the cockpit battle for the controls.

Another possibility is that the suicide pilot shot or otherwise disabled the other two crew members before implementing his flight to doom. This almost makes more sense, but it still leaves open the question of how he was able to disable them: a gun? Some kind of spray? A struggle would still have to take place.

A second question is, which of the three flight crew members may have done it? The award-winning Zhang Zhengping would seem least likely, having invested his life in his career. The CAAC investigated the backgrounds of all three of the crew and found nothing unusual such as outstanding debt or personal troubles that would obviously account for suicidal intent.

A third possibility is that someone from the passenger area broke into the cockpit and forced the plane to the ground. This involves the question of how mechanically difficult such a feat might be.

A cursory internet search reveals that there are no private bathrooms in airliner cockpits, meaning that the door to the passenger area has to be open to allow pilots to answer calls of nature. Updated regulations after 9/11 mandate that at least two crew members must be in the cockpit at all times, so for example, only one pilot on Flight 5735 could leave the cockpit at a time. A patient terrorist with a first-class seat having a view of the cockpit door could therefore wait until the door opened and make a threatening move, perhaps holding a flight attendant hostage at knifepoint (assuming he could smuggle a knife on board). But he would still have to overpower three determined flight crew members to do the dastardly deed.

Well, I think we’ve had enough of these dismal speculations for one column. Suffice it to say that deliberate human action looks like the most likely explanation for the fate of Flight 5735. We may never know much more than that, unless there are clues in the cockpit voice recorders that remain to be unveiled. Despite all the modern technology that is deployed to ensure air safety, as long as people fly the planes, we have to trust those people. And once in a very great while, someone decides to betray that trust.

This article has been republished from the author’s blog, Engineering Ethics, with permission.

Karl D. Stephan received the B. S. in Engineering from the California Institute of Technology in 1976. Following a year of graduate study at Cornell, he received the Master of Engineering degree in 1977...