Potential Causes: Exploring the Possibilities of a China Eastern 737 Crash

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There has been little news from China regarding the China Eastern 737 which crashed last week, but from what we know we have some possibilities to include and exclude.


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What do we know about China Eastern Flight 5735?

Very little is known about the crash of China Eastern Flight 5735. It was on a routine flight between Kunming and Guangzhou, the airline’s hub near the southeast border with Hong Kong. The 737-800 (NG – New Generation) was carrying 123 passengers and nine crew according to sources when it lost altitude significantly from 29,100 feet (cruise) plunging into a mountain below.

Purported video of the crash showed a vertical arrow plunging down the side of the mountain, causing an explosion and a plume of smoke.

Flight tracker data showed the plane appeared to recover around 7,000 to 9,000 feet before continuing shortly after its fatal crash. The black box has been recovered and because the plane was made in the United States, federal investigators will join the effort to figure out what caused the crash with Chinese teams.

At the time of publication, neither a recording of communications with air traffic control (ATC) nor a transcript was available.

Some possibilities

Many have speculated as to the cause of the accident and as someone who has followed aviation and subsequently air accident investigation, some of the earliest possible causes seem to be guesswork. I have no inside information, but some speculations seem less believable than others for several reasons.

Break in flight

One of the notions passed down was that there was some sort of in-flight disintegration of the plane that caused it to fall out of the sky. One of the reasons this theory would be successful is that there is a lack of direct communication with ATC. We don’t know at the moment. The other plausible reason is that aircraft parts were found separated from the incinerated wreckage.

The reason I think this is unlikely is that the recovery has been noted. If the plane was split in the air, there would be no recovery, just a straight drop from the sky and probably in multiple pieces (more than has been demonstrated in the media) with a range of debris. That said, it is also possible that the data indicating a recovery is wrong.

Footage appeared to show the winglet and part of the wing had detached and remained intact away from the crash site, and although the video was poor quality, it was difficult to make out a vertical (tail) stabilizer in the video. This suggests that something happened to separate these parts, but a drop of this magnitude could have had the same result.

Terrorism/hijacking

Typically in a terrorism and hijacking situation there is usually something as simple as a squawk code 7500 which indicates ‘unlawful interference’ as one of these events or a simple 7700 which simply demonstrates an emergency and is used more generally.

That’s not to say something couldn’t have happened before the pilots had a chance to point it out, but there was sort of a check briefly at altitudes of 7000-9000′, so even with a struggle where control was regained temporarily, it wasn’t indicated. The problem of dismissing it due to the lack of a 7500 or 7700 squawk is twofold. First, it’s possible that the pilots indicated it but it didn’t work properly, second is that in an air emergency, the priority order changes to “aviate, navigation, communication”. The brief period of control may demonstrate that they were still trying to navigate.

The media made it clear that there was no known “Mayday” distress call, so it seems unlikely, even on a perilous dive, that it didn’t come from one of the two pilots. .

Software/MCAS

The Boeing 737 is the most prolific aircraft ever produced. This particular model was a 737-NG ruling out a resurgence of MCAS software that brought down planes in Ethiopia and Indonesia that were found responsible for the 737-MAX crashes. This aircraft was not equipped with MCAS and had none of the difficulties with software that seemed to demonstrate a standoff with computers that other crashes have had.

Suicide/Pilot Health

Intentional shooting down of the aircraft by either or both pilots is possible. Protocol has changed since German Wings 9525 in which the co-pilot who had been treated for suicidal thoughts, locked out the captain and crashed the plane into a mountain. If both pilots were suicidal or the protocol to leave a flight attendant in the cockpit when going to the bathroom was not followed, then that is a possible cause.

This cause would explain the aircraft’s limited recovery (in the event of a struggle) and the entire nose-down attitude of the aircraft on impact.

It’s also worth noting that this possibility also explains another data point, which is that the plane appears to be pushed or headed down rather than just falling. This again comes from the attitude but also from the rate of fall which seems to exceed the natural rate of descent of objects at this height reaching the ground in free fall. Curiously, the speed fluctuations are also weird.

A question that remains was how a piece of the plane was later found far from the wreckage, but intentionally pushing a plane on the ground at this speed could have knocked out pieces of the plane that could not support the stress.

Bad data

Many tipsters focus on the recovery, as I also noted. It’s entirely possible that the recovery never happened. If the aircraft had encountered some sort of catastrophic failure at altitude, the reliance on faulty equipment is questionable. If the ground radar also detects the recovery, that possibility is eliminated, but for now it must be at least possible that the preliminary data is bad and that this leads to false assumptions.

Mechanical problem

There were only 11 fatal incidents out of more than 7,000 737-NGs in service. Unlike jumbo jets that can only fly once or twice a day, these high-performance aircraft are used on shorter flights, resulting in many more take-offs and landings each day. Much more wear and tear on the equipment increases the risk of mechanical problems.

This particular aircraft was manufactured in 2015 and is considered relatively new as most aircraft remain in service for over 20 years. That said, mechanical issues can arise based on something that happened on the ground, over time, or encountered in flight. Maintenance records will be reviewed over the coming weeks, months, and possibly years to determine the direct cause.

Quick decompression

One concept that is not discussed enough (in my opinion) is the altitude at which the plane appeared to temporarily regain control. During a rapid decompression event, one of the first orders of the day is to descend below 10,000 feet where passengers can easily breathe without the need for oxygen pumped from aircraft systems.

If there had been any rapid decompression, the rapid descent (negative vertical speed greater than 20,000 feet per minute) would have been obvious, but it is possible that if there had been something causing the pressure to drop to the plane the pilots may have tried to descend below 10,000 feet for this purpose initially, but the problem causing the decompression remained and the plane became unmanageable as a result of the release.

Conclusion

It is impossible to know what caused this crash in the first place. Even with cockpit and ATC transcripts or recordings, the information could turn out to be incorrect or erroneous, just like the data. Investigations of this nature can take years to resolve. However, key data points (a mostly intact debris field and recovery at 7,000-9,000 feet) make this accident particularly enticing.

What do you think? Do you have any ideas on what could have caused this accident? What do you think of the data points?

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