In the previous installment, Comet overcame numerous difficult technical challenges to reach commercial flight.
Their debut was spectacular, but it also presented the unique challenges of being a world first.
However, unfortunately, an unfortunate accident occurred.
This time, we will introduce the unfortunate accident and the investigation into its cause.
Comet Serial Crash
And then the worst tragedy finally struck.
Moreover, the plane crashed three times in a remarkably short period of time.
Third plane crash
The first incident occurred in May 1953, when a Comet lost communication six minutes after taking off from India, its transit point.
The aircraft entered a strong thunderstorm, disintegrated in mid-air, and crashed.
Sadly, a total of 43 people died: 6 crew members and 37 passengers.
The Indian government's investigation into the accident site concluded that the cause was due to pilot error, which overloaded the aircraft and caused it to break down.
In response to this speculation, pilots pointed out that the Comet's control stick felt too light and that they didn't get much feedback on the aircraft's behavior from the control stick, prompting the manufacturer to take immediate action.
In this accident as wellSimilar to the warnings leading up to the accident, pilot error was the primary cause of the incident. However, some argued that the pilot of the crashed aircraft was a highly skilled veteran and therefore could not have made such a mistake.
Ultimately, the cause was never identified, but for some reason, the aircraft was able to fly again soon after.
This is quite puzzling to me, and if human lives have been lost, the first thing I would do is prohibit the use of that machine.
Furthermore, if it were transportation equipment, the government's certification would likely be revoked.
moreoverUnless the cause is identified and effective countermeasures are implemented, recertification and permission for reuse are not possible.
But for some reason, it took off again this time.
In my humble opinion, the overconfidence in their own technology, stemming from the government's (Great Britain's) restoration and the manufacturers' pride, led to the aircraft's return to flight.
Third plane crash
The second incident occurred in January 1954 when a Comet aircraft that had taken off from Rome, Italy, heard a loud explosion while communicating with another plane over the Mediterranean Sea, and lost contact.
The plane exploded in mid-air just 20 minutes after takeoff, breaking apart and crashing. Apparently, some fishermen nearby happened to witness it, seeing the aircraft explode and its parts fall into the sea.
Sadly, 35 people died, including 6 crew members and 29 passengers.
Perhaps realizing the seriousness of the situation, they suspected it was caused by aerial fires, which were frequent in other aircraft models at the time, and implemented fire prevention measures in the fuel and electrical systems, as well as installing additional smoke detectors.
Furthermore, thorough retraining of the pilots was carried out.
HoweverThe true cause could not be determined, and it was suspected that the fire was caused by an irregularity or accident, so the flight was resumed.
In my opinion, permission for another flight is out of the question.
Third plane crash
The third incident occurred in April 1954, when a plane exploded in mid-air and crashed over the Mediterranean Sea near Naples, Italy, at an altitude of approximately 10000 meters.
Unfortunately, all 21 people, including 7 crew members and 14 passengers, are still listed as missing.
As expectedThree plane crashes occurred within a period of about six months.Taking the matter seriously, they finally revoked the flight permit and began a full-scale investigation.
Summary of the accident timeline
Add the events up to this point to the snake diagram.
If you've read this far, most of you are probably thinking, "That happened 70 years ago, and in this day and age, such a thing wouldn't happen and wouldn't be tolerated."
That's exactly the same situation in large Japanese corporations today (one of the reasons I left my job).
Modern companies' market response to problems
To give you an idea, the company I used to work for is known by about 80% of people worldwide (regardless of whether they're in a developed or developing country), and I think it's generally perceived as a company with strong technology.
In Japan, if you watch TV for 30 minutes during prime time, you're almost guaranteed to see their commercials.
As is the case in any company, designers work with the quality department when problems arise in the market. Naturally, this is a job I have done many times myself.
First, we create a flimsy argument to insist that the customer's usage was inappropriate. This is the same approach we used in the first Comet jet crash.
When I absolutely can't come up with a rationale, I diligently search for a reason, thinking, "There must be a problem with the manufacturing process."
If the cause still cannot be found, they will implement some superficial measures (often simple structural reinforcements) and offer a plausible explanation to the customer. This is the same response as in the second Comet crash.
The problem will recur in the market.
This is a repetition.
As you can see with a little research, the reason why products are recalled, retrieved, and repaired multiple times due to the same defect is because of these kinds of structural flaws within the company.
When the same problem occurs about three times with many customers, it's only natural that they'll finally take action, form a specialized team, and start investigating the cause.
This is no different from Comet's response. This is reality.
The reasons why products with many defects are not addressed are that they are not profitable, so there is no motivation to do so, and because it is not a job that is highly valued within the company, there are not many people who are proactive in doing it.
The culmination of this kind of corporate culture is the recent, well-known incident involving Mitsubishi Motors' truck accident and subsequent cover-up of recalls.
I sincerely hope that the corporate culture of many companies has improved (although I doubt it has).
From historyLearning and putting things into practice is difficult. It's especially difficult in large organizations.
Investigation into the true cause of the Comet series of crashes
Given that the Comet incident itself was a matter of national prestige, a thorough investigation into its cause was also a matter of national pride.
Under then-Prime Minister Churchill, a task force was formed, bringing together government, military, and civilian personnel, and funded by the national budget.
It's the strongest team: a government-civilian-military alliance.
I believe it's a great pity that in present-day Japan, constitutional issues make it difficult to achieve cooperation between the government, civilians, and the military (though Japan never had a military).
Leaving that aside...The investigation into the cause of the Comet malfunction is exactly the same as how many companies currently handle market defects, and it reveals the flow of application of reliability engineering, which is essential when developing new machinery.So let me explain in a little more detail.
Of course, I will dedicate specialized sections to explaining these topics in detail in this blog's mechanical design course.
Until around 1990, Japan had a very high level of quality technology, including reliability engineering. I find it baffling why universities and companies stopped emphasizing its teaching when I was a student (less than 20 years ago).
Investigation into the cause of the Comet aircraft crashes begins.
The first thing to do is exactly the same now as it was in the past, as I have mentioned many times in the section on fracture in materials mechanics.We made efforts to collect as many parts as possible from the crashed aircraft.
They apparently spared no expense in their search. I don't really want to write about this, but they also searched for a body and conducted a thorough autopsy.
Impressively, with the cooperation of the military, aircraft carriers, destroyers, and patrol planes were also deployed.
The destroyer used sonar to search for the fragments, and when they found a suspicious spot, divers would dive down and retrieve them.
Even so, they apparently didn't have enough ships and had to charter private trawlers (ocean-going vessels).
Furthermore, all three accidents occurred outside of their own territory, and while it is extremely difficult for the military to enter another country's territory for any reason, it seems that Britain, being a professional diplomat, managed to find a way to make it happen.
This kind of tenacity is truly befitting of the British Empire. Whether the modern Japanese government or Japanese companies could do the same is highly questionable.
Next, you put the collected parts back together as much as possible, like a puzzle, using what may not be all of them.
As I've repeatedly mentioned in my discussion of fatigue fracture in mechanics of materials,Even today, when a prototype breaks down during development testing or a problem arises in the market, we do exactly the same thing.
The goal is to collect as many defective products as possible, sometimes even by offering a reward (a certain manufacturer is still collecting water heaters/boilers, right?).
I was fortunate enough to be involved in the development of racing car engines when I was a rookie, so prototype engines broke down almost every week. I would get yelled at, but I would work hard with the testing department to pick up the broken parts (it was tough, but a valuable experience).
This method was supposedly first used in the Comet jet crash, but that's probably a lie.
As far as I know, around the time of the start of World War II, when a Japanese Zero fighter plane broke apart in mid-air due to flutter during a dive test, they collected the scattered parts, reassembled it, and tried to figure out the cause.
There's a 99% probability that this kind of restoration work has been going on for much longer than this, and I'm simply unaware of it.
Putting that aside, returning to the Comet, I meticulously checked the fracture surfaces of the parts while simultaneously reassembling the scattered components.
If the fracture surface is not visible due to dirt or crushing, clean it little by little while taking pictures (to keep a record) and check it. If it still cannot be seen, polish the fracture surface slightly.
That's how it worksBy examining the fracture surface of a component and determining the type of failure (single-shot failure, fatigue failure), it becomes possible to determine which components failed and in what order.
Example of a cross-section of a single-shot destruction
Details of the one-shot destruction can be found here.
An example of a fatigue fracture cross-section. A characteristic shell-like pattern is visible.
For details on fatigue failure, click here.
For example, a fatigue fracture surface may develop in a certain area of part A, eventually leading to a sudden failure. Part A will then fly off and collide with part B, causing part B to fail and then part C... an experienced engineer can predict this process to some extent.
By working backward from this puzzle, you can figure out which part was destroyed first, and even which part of the component was the starting point of the destruction.
In the investigation into the Comet accident, these investigations revealedIt appears the cause was fatigue failure originating from the corner of the pilot's cabin window and from the antenna hole on the top of the aircraft.This was the analysis.
If fatigue failure is identified as the cause of the accident, it means that repeated loading or stress caused by some kind of stress was the culprit.
Formulating hypotheses about the cause of the Comet crash based on circumstantial evidence.
Then nextLet's consider a hypothesis (story) about what is happening and how repeated loads and stresses are generated.
The ideal approach would be to gather experts from various fields, of course, but also include people who might seem unrelated, and simply list all the possible events that could occur.
Thinking about this phenomenon is difficult if you're suddenly asked, "Okay, now tell me your thoughts," so methods like brainstorming and design thinking can help with that process.
I'll explain this later, but it's become quite popular recently, although the method itself isn't anything special and I think it's been done empirically for a long time.
Next, organize the possible events listed in the following way.
Well-known methods for organizing data include FTA, FMEA, and cause-and-effect diagrams.
As far as I recall, FTA and FMEA were products of NASA's Apollo program, so I don't think they existed at the time of the Comet crash, but I believe similar measures were being taken.
Cause-and-effect diagrams didn't even exist at this time. This concept originated in Japan.
FTA (Fault Tree Analysis)
To give a brief overview, FTA (Fault Tree Analysis) is called the analysis of a fault tree, and in the case of the Comet crash, the top event is fatigue failure of the pressurized chamber, and then the factors that cause fatigue failure of the pressurized chamber are listed.
Next, identify the phenomena that must occur for each of the factors listed to result in that factor. Repeat this process over and over.
In other words, by gradually analyzing the events that occurred, we can eventually identify all the factors that could have caused those events.
FTAA key characteristic is that the process starts with the event itself, then breaks it down into smaller and smaller parts to find the cause.
FMEA (Failure Mode and Efficient Analysis): Analysis of the effects of a failure.
On the other hand, FMEA (Failure Mode and Effective Analysis), which stands for Failure Mode and Effects Analysis, is the opposite of FTA. It considers what kind of failure a component might have initially caused, and how that ultimately affects the entire Comet.
In other words, you can first consider all possible ways in which the product's components could fail, and then identify everything that would happen to the entire product if those components failed.
FEMAA key feature is that the process starts with the components and traces back to the event that caused the problem.
Cause and effect diagram
The final cause-and-effect diagram is also called a fishbone diagram because it resembles a fish's bone, and it's a way to think about what factors caused an event to occur.
For example, when equipment breaks down, we investigate the cause by considering factors such as human error, machine error, improper use, faulty materials used, or incorrect measurement methods.
These five elements (Man, Machine, Method, Material, Measure) are sometimes referred to as the 5Ms.
The characteristic of this cause-and-effect diagram is,The key is to consider the influence of the surrounding environment of the machine being used.
Well, I'll explain the details in the mechanical design course, but I think many people have heard of this in their work, even if they're not engineers.
I personally dislike it, but it's a tool used in QC circles, which are loved by many Japanese companies, and I'm often made to use it in training.
In this way, if problems arise during development testing or in the market,By considering the probability of each event occurring, we can derive the hypothesis that is most likely to occur.
またBy leveraging the unique characteristics of each analysis method, we can consider factors from an event-based, component-based, and environment-based perspective, preventing any omissions or oversights.
The author recalls doing this every day for about a year and a half because prototype engines were breaking down almost every week. He also remembers sorting through his dreams and realizing that his health might be in serious trouble.
The Comet plane crash was probably handled in a similar way to arrive at the most likely hypothesis for the cause of the crash.
The derived hypothesis
The hypothesis that was derived was,The cause was described as "mid-air disintegration due to fatigue failure caused by repeated tensile and compressive loads resulting from fluctuations in the internal pressure of the pressurized chamber and atmospheric pressure," and further stated that "stress concentration occurred at the corners of the windows and the holes in the antenna."That's what I thought.
In response to this hypothesisThe company that developed and manufactured Comet met with strong opposition.
That's only natural.Even today, and even back then, stress concentration at corners and fatigue failure due to repeated loading are fundamental aspects of mechanical design. Naturally, they took these factors into consideration.
Furthermore, it was confirmed through prototypes after undergoing rigorous durability tests meticulously designed by the elite engineers of the British Empire.
fundamentallyIndustrial products are developed and mass-produced by repeating the cycle shown in the following diagram.
The author speculates that the government, having granted approval, likely felt a strong sense of pride in the aircraft's defects and therefore strongly opposed the idea.
If that hypothesis were true, it would be like saying that the considerations, tests, and checks devised by elites from both the public and private sectors were completely inadequate, which would be a huge loss of face for them (and the same thing is happening frequently even now).
Amidst strong opposition from both government and private sectors, the RAE (Royal Aeronautical Research Institute, similar to the technical department of the Royal Air Force), which had no vested interest in the matter, took the lead in advocating this hypothesis.
As expected of Prime Minister Churchill, he didn't get swayed by public opinion and listened to the RAE's arguments.
Up to this pointThe conclusions drawn are merely hypotheses, so they are meaningless unless they are proven.
Hypothesis and verification areIn the world of engineering, they must always be considered together.
From this point on, it became a political battle, but fortunately, RAE had the capability to conduct its own tests, so it decided to conduct fatigue tests under new conditions on its own.
However, the author predicts that even though the RAE has no vested interest, they cannot conduct the trial without permission, and moreover, they simply do not have the funds.
The author speculates that Prime Minister Churchill made the decision to fund and authorize the experiment despite opposition from those around him who considered it a waste of money.
I'm curious how the mass media, such as the BBC, reported on it at the time. I'll look into it later.
In my estimation, even if the BBC and other media outlets were considerably better than the Japanese media, they would likely have still broadcast the fatigue breakdown theory as a far-fetched idea, indicating the general public's skepticism towards this hypothesis.
I think Prime Minister Churchill and the RAE took incredibly courageous actions in that environment.(Is there anyone among the current leaders who can make decisions?)
This is where the RAE's lonely battle begins (though Churchill is backing him).
Next time, I'll mainly explain the demonstration experiment at RAE.
To those who found this article helpful in understanding design:
Since we're on the subject, I'd like to recommend a book that's essential for mechanical design.
To be honest, the content is extremely unhelpful, but it can be used like a dictionary when you forget the details. If you read this article, you should be able to understand the content and use it effectively. It also includes commonly used standards, making it quite useful.
If you don't already own one, I highly recommend getting one, even though it's a bit pricey. However, new ones are expensive, so if you're considering buying a used one, I strongly recommend checking that the surface roughness conforms to the new JIS standard.
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