What Caused the JL123 Crash?


When I first started conducting research about the JL123 crash (also known as JAL123), I had no intentions of looking at the cause of the crash at all. As far as I was concerned, it was a known fact: following an accident in 1978, the rear pressure bulkhead was damaged, incorrectly repaired, and this led to the bulkhead giving way during flight JL123, with the air rushing out of the cabin into the tail section and leading to damage to the plane that made it ‘uncontrollable’.

The following diagram shows what is assumed to have happened.

Source: https://commons.wikimedia.org/wiki/File:Japan_Airlines_123_-_Rear_destruction_process_ja.svg

Soon after starting my research – which I had intended to be focussed on the memorialisation side of the crash – I began to read Japanese books about the crash and was shocked to discover that there were many questions being raised about the cause of the crash. While some of these gave suggested causes that I found it hard to accept, the key point of all of the books which discussed the official report is that they showed how there were elements of that report that made no sense.

I am not a plane engineer. My primary expertise when it comes to JL123 is still looking at the memorialisation and issues relating to the dramatizations and documentaries connected the crash. However, during the course of my reading of various books and reports, as well as knowledge gained from watching plane crash documentary series, combined with using the analytic skills developed as an academic, I felt, by the time that I finished writing Dealing with Disaster in Japan: Responses to the Flight JL123 Crash that I had reached a position where I understood what may have caused the accident.

To date I’ve not written about this on my site, but after the release of the Plane Crash Recreated: JAL123/Japan episode on TV, which is one of the first English-language documentaries to at least raise the issue of the possibility of the official report being wrong about the ‘probable cause’, it is time to provide some more detail here.

I am not going to go through all of the various theories about what may have caused the JL123 accident. I am going to set out why I have an issue with the conclusion of the official report and what I think could have happened.

The starting point for my concerns with the official report is that there is no evidence that the usual things that are associated with rapid decompression (a requisite of the basis for the ‘probable cause’ in the official report) happened. If we look at the comments given by the survivors and in notes (isho) written by some passengers, there is absolutely no mention of air rushing out of the cabin. There is mention of some mist in the cabin – but it was not moving.

On top of this, we have the issue of what was happening in the cockpit. We know that the cockpit crew did not don oxygen masks. And yet the plane remained above a safe altitude for a significant period of time, as can be seen in the following diagram from my book. The dark and light grey areas show the period above the altitude that the plane should have descended to in an emergency, while the dark grey area shows the period where the plane was at an altitude where there would not be sufficient oxygen.

The official report suggests that the fact that the plane was at the unsafe altitude accounts for the lack of conversation in the cockpit and suggests that the crew were suffering from hypoxia. At this altitude for so long, hypoxia is the absolute minimum someone would have been suffering from. But if they had hypoxia – how did they continue to control (as best they could) the plane during this time? They would have had no, or limited, bodily functions at this time, not just a lack of speaking ability.

On top of this is the evidence related to the pilot’s remains. Part of his jaw was found at the crash site and the teeth were ground down. According to his wife, this must have happened during the flight. If he were grinding down his teeth – likely due to the strain of the situation and trying to fight with the plane – he could not be speaking at the same time.

All of this points to the possibility – or rather, probability – that rapid decompression did not happen.

In my view, I think that one possibility of what could happened is that the aft pressure relief door did not function properly. According to the official report, the aft pressure relief door, which was found at the crash site, showed some signs of damage, but it was suspected that this damage was caused when the plane crashed and there was no reason to think that the door had not functioned at it was supposed to. In my view, this assumption has ruled out an important possibility.

Let us return to the diagram introduced above, but make one modification. Let us assume that the aft pressure relief door remained shut for some reason. I have shown the ‘explosion’ at the pressure bulkhead in each image as I will discuss what may have happened there further below.

Just by having the aft pressure relief door remain shut, the scenario otherwise plays out exactly the same.

So what happened at the rear bulkhead? If we’re now assuming that the aft pressure did not open, it also means that the breakage at the rear bulkhead needn’t have been so great. Rather than a massive tear or hole appearing, some pressurized air merely needs to be escaping into the tail section for the whole scenario (which is completely consistent with the rest of the official report) to play out. There just would be no rapid decompression, but some decompression (the fact that pressurized air would continue to be put into the cabin from the engines would have limited the impact of how much pressurized air was lost through the relatively small hole(s) and the impact on the upper deck (where the cockpit was) would likely be minimal), but not rapid. There was evidence to suggest that there had been problems with this plane (doors not opening/closing properly at the back of the plane) leading up to 12 August 1985 which may be consistent with cracks having already got large enough to allow some air into the rear section prior to flight JL123. On flight JL123 the cracks and amount of pressurized air in the aft section reached a tipping point that allowed for the fatal damage.

It was very odd visiting the JAL Safety Promotion Center one time after I had reached the above working theory, and seeing the aft pressure relief door there. I had forgotten it was there. I was there with an NHK TV-crew, but luckily they didn’t film me (as far as I know) when I asked it what happened to it. If only it could answer.

One point that gets overlooked, whether you agree with my theory or still think the official report may be correct… the Boeing 747 (which, keep in mind is my favourite plane – see for example my post “Boeing 747 Model – Owning a part of an actual B747” ) has a fundamental design fault. In fact it’s not only the 747, this is, as far as I’m aware, in all commercial jets. While there are so many ‘redundant’ features on these planes – there specifically in case the primary thing doesn’t work or breaks – there is no redundancy for the rear bulkhead. This is despite the fact that Section 2.1.3 of the British Civil Aviation Regulations state that ‘the primary structure shall be designed to withstand any pressure differences which might exist between compartments and, in particular, to withstand the effects of sudden release of pressure’. To put it another way, planes without an additional bulkhead are effectively illegal (at least in the UK), but nothing has been done about this. Had there been an additional bulkhead it is almost certain that the JL123 crash would not have happened, even if the pressure relief door would not have opened. This is something that the airline industry still needs to address.

As for JL123, I hope that discussions will continue about what actually happened. There is further evidence out there to be investigated fully – taking advantage of advancements in technology that would allow for further analysis of existing materials, let alone taking account of evidence ignored in the original investigation, and ensuring that potentially important evidence still sitting in Sagami Bay is retrieved. Until this happens many families of those who lost loved one cannot get ‘closure’. Until this happens, the souls of those who perished in the crash may not be able to rest in peace.

You can find out more about my research on the JL123 crash here.

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