Up to this point, we have covered the events from the Comet crash to the identification of its cause.
This time, we will mainly summarize the commonly cited findings and lessons learned from engineering.
However, based on my own experience, when I look at the Comet jet crash, it's difficult to believe that it was simply a matter of engineering problems, especially knowledge of materials mechanics.
Therefore, I will explain the general findings in the first half, and then in the second half, I will introduce the author's own thoughts.
First, let's look at some of the general engineering insights and lessons learned.
Engineering insights and lessons learned from the Comet jet crash (general lessons)
It might sound a little tedious, but let's review the key points of the Comet jet crash.
First, let's look at what made the Comet an unknown territory compared to existing passenger aircraft.
Comet's engineering novelty
First, let's highlight the key points of what made Comet a world first in terms of engineering.
1. It uses a jet engine as its power source.
2. It employs an unprecedentedly large pressurized chamber.
3. The aircraft cruised at an altitude vastly higher than any previous commercial commercial flight.
If you look closely, there are many other innovative aspects to the technology, but if we were to broadly summarize the key points, I think it would come down to these three.
To explain it more logically and accurately, the adoption of jet engines for high-altitude, high-speed cruising flight has made it possible to fly at altitudes and speeds incomparable to before.
In order for humans to fly at high altitudes while maintaining their lives, a large pressurized cabin large enough to accommodate all the crew members became necessary.
In other words, a couple of new technologies were needed to address the problems that arose as a result of adopting jet engines.
Probably, at that time,I believe that we may have focused so much on the innovativeness and challenges of this jet engine that we neglected to consider the larger issues lurking behind it.
A slightly more detailed history of aircraft engine development can be found here.
The birth of the jet engine
A slightly more detailed explanation of the pressurized chamber can be found here.
Design challenges for pressurized chambers
In any case, the Comet achieved the glory of being the world's first after being developed in a relatively short period of time, but unfortunately, it suffered a series of crashes shortly after commencing commercial flights.
Next, let's review the causes of the plane crash.
Engineering causes of the Comet plane crash
The engineering cause of the Comet crash can be explained by the following logic.
1. Because it was an airplane, repeated loads (pressures) were applied to the pressurized cabin due to pressure fluctuations caused by altitude differences with each flight.
2. Stress concentrated (load concentrated) at the corners of the aircraft's windows and at the antenna holes.
3. The aircraft's fatigue strength was insufficient to withstand repeated loads caused by stress concentration, resulting in failure in a much shorter time than expected.
Becomes
Perhaps because they were so worried about and focused solely on the jet engine, the engine malfunction itself wasn't the direct and fatal cause, but rather the problem manifested in the airframe.
To put it simplyThe aircraft's (pressurized chamber's) strength was simply insufficient to withstand the actual load.
Details of the investigation into the cause of the Comet plane crash can be found here.
Next, let's review why, despite thorough testing during development, the aircraft crashed due to fatigue failure.
The cause of the engineering miscalculation regarding the structural strength of the Comet aircraft.
The cause of the Comet crash could not be determined by the development and manufacturing companies alone, and was only revealed through reproduction tests conducted by the RAE (Royal Aeronautical Institute).
Let's review the specific differences between the development and manufacturing companies and the RAE's reproduction tests.
First, let's review the main points of testing conducted by development and manufacturing companies.
1. The aircraft (pressurized chamber) was divided and tested.
2. To confirm the aircraft's strength to withstand a single hit, it was subjected to twice the expected load.
The parts tested in section 3.2 were used directly in the fatigue test.
4. As a precaution, under the fatigue test conditions, twice the expected load (pressure) was applied at a rate of once every 1000 cycles.
These four points are the most important.
On the other hand, let's review the key points of the tests that the RAE conducted.
1. The aircraft (pressurized chamber) was tested in its completed state without being disassembled.
2. The actual load (pressure) applied was faithfully reproduced.
These are the only two main points.
in just This small difference had a significant impact on the test results, and a tragic accident actually occurred.
Here's a look at the causes of the Comet crash and the differences in testing.
From this, the following lessons and countermeasures are generally taken.
Engineering lessons and countermeasures from the Comet jet crash
Generally, the causes of the Comet crashes are summarized as follows:
- There was a lack of knowledge regarding metal fatigue.
There was a lack of knowledge regarding the effects of stress concentration on metal fatigue.
The following measures have been taken to address this cause.
• The structural integrity of the aircraft must be checked only after it is completed.
- Round off corners where stress is likely to concentrate as much as possible.
- Aircraft strength tests must be conducted separately using a single-shot destruction test and a fatigue test.
- Aircraft in commercial flight must undergo non-destructive testing (using sound waves or magnets to check for internal cracks) during maintenance.
Becomes
This measure is, of course, still in effect today, and the easiest way to understand it is to see that even in modern jet passenger planes, the cabin windows are quite small and almost oval or circular in shape.
Furthermore, fatigue testing of the aircraft (pressure chamber) is conducted using the entire aircraft (pressure chamber).
In most cases, the countermeasures and lessons learned from the Comet crashes end here.
However, this is merely one perspective, and it simply means that the engineering cause was identified and countermeasures were taken.
Comet SeriesThe lessons learned from this plane crash leave a very serious question: are these the only lessons we can learn?
Next, based on my own experience, I will examine the causes and lessons learned from the Comet jet crash.
Reconsidering the causes of accidents
From here on, I'll be expressing my own opinions without reservation.
Based solely on the lessons and countermeasures discussed so far, only the structural (engineering) problem of the jet passenger aircraft's airframe (pressure chamber) can be solved.
Simply create a checklist and use that.
So, when humanity ventures into uncharted territory again, and many lives are lost, will we be able to simply say, "It was due to a lack of engineering knowledge"? I strongly believe this.
In other words, To simply dismiss the Comet crash as a lack of engineering knowledge is tantamount to saying that if casualties occur when we venture into uncharted territory in the future, "these are unavoidable sacrifices for the advancement of engineering."
Indeed, the British judiciary did not impose legal sanctions on any parties or organizations involved in the Comet crash, including the development and manufacturing companies.
The reason given is that the operating environment was completely different from that of previous passenger aircraft, and it was uncharted territory in aviation technology, making it impossible to predict the risks.
However, just because no legal sanctions were imposed, can we truly say that there were no problems other than engineering issues? A major question remains: is it acceptable for human lives to be sacrificed when we venture into uncharted territory once again?
Although no legal sanctions were actually imposed, the series of accidents led to a loss of confidence and a prolonged suspension of operations, which not only ruined the development and manufacturing company (de Havilland) but also caused the entire British aviation industry to lose its global dominance.
For example, even if the world's first space travel becomes a reality in the near future, if an accident occurs immediately, resulting in numerous casualties, the explanation that "it was due to a lack of engineering expertise" cannot be accepted.
If an accident like this were to occur and the press conference announced, "This was an accident caused by a lack of knowledge due to being in an uncharted territory," it's easy to imagine that the anger and grief of the victims' families would not subside, but rather be inflicted even deeper wounds.
That's not true.While it is absolutely unacceptable, humanity's venturing into uncharted territory will never be stopped.
Then,The lessons we should learn from the Comet jet crash cannot be fully understood without examining both the hardware and software aspects, not just from an engineering perspective.
Here, "hardware" refers to things that can be expressed primarily numerically, such as the Comet itself, testing equipment, money, and time, while "software" refers to abstract concepts such as the people and organizations involved, organizational management, development systems, and accident response.
Incidentally, there are various perspectives for checking the activities of such companies and organizations, such as people, things, money, and even adding information, or McKinsey's 7S framework, but in my opinion, none of them are sufficient, so I divide them into two main categories: hardware and software.
I believe that failing to take a comprehensive view of the entire plane crash at the time would be extremely disrespectful to the victims and those involved.
First, let's take a general look at the Comet problem and the surrounding stakeholders (government, corporations, etc.).
Comet and its surrounding stakeholders (government, corporations, asset management companies, etc.)
First, I will state my opinion based on my own experience.
Comet too, certainlyWhile it's true that there was a lack of engineering knowledge in an unfamiliar area, the probability of a total of six accidents, including three consecutive crashes, occurring due to that single cause is extremely low, or rather, impossible.
In other words, I believe there were significant problems beyond just engineering issues.
In this case, first of all, when we look at the responses of the organizations surrounding the Comet and the accident, we see many instances of rather unnatural handling of the situation.
One of the biggest inconsistencies is that the flight permit was not revoked after the first crash, even though the cause of the accident had not been determined.
Because normally, the organizational structure, operational methods, and accident response would limit the number of incidents to one at most.Therefore, even if the possibility of pilot error or an irregularity is high, flight clearance will not be issued unless the cause is identified and corrected.
In other words, The risks in uncharted engineering areas are minimized to the greatest extent possible through the development organization, national certification systems, and the mechanisms of the commercial flight operators.
FirstIt's hard to believe that the problem wasn't just an engineering issue, but also a major problem with the actions and oversight systems of the surrounding related organizations.
Ideally, not only the aircraft (Comet) itself, but all surrounding stakeholders would check the Comet from their respective perspectives, and furthermore, each organization would check whether the others are functioning properly, thereby ensuring that any abnormalities or malfunctions are quickly and comprehensively detected (multi-perspective checking and mutual checking).
In this way, the engineering risks in uncharted territory are minimized by effectively utilizing the organization's resources.
Furthermore, by checking for abnormalities or malfunctions from multiple perspectives, accidents can be detected and addressed before they occur.
Therefore, it is likely that the true cause of the series of crashes was not simply a defect in the aircraft's structure, but that other factors also played a significant role.
For example, if the first crash had been thoroughly investigated instead of simply attributing it to pilot error, there's a very high probability that the other two accidents would not have occurred.
Furthermore, two major accidents had occurred before the first crash.
If a thorough check had been conducted at that time, instead of placing all the blame on the pilot, the crack in the aircraft might have been discovered.
In the first place, there is a law called Heinrich's Law which states that "for every major accident, there are 29 minor accidents and 300 near misses."
Based on my experience and intuition, I have doubts about this number.I believe it's true that before a major accident occurs, there are usually several minor incidents and many small malfunctions.
In other words, In the case of the Comet, if the surrounding check system had been functioning properly, I believe that a fundamental response could have been taken at the stage when the malfunction was discovered or a minor accident occurred.
The facts show that accidents and malfunctions had occurred before the first Comet crash, and there were plenty of clues that could have led to the accident.
A major accident that occurred due to insufficient multi-perspective and mutual checks.
A recent example of an irreversible major accident that occurred through a similar mechanism and had a tremendous impact on us Japanese people is the Fukushima Daiichi nuclear power plant accident.
It is true that we encountered an extraordinary situation when a massive tsunami, triggered by an earthquake of unprecedented magnitude, struck (uncharted territory).
However, the multiple safety devices and auxiliary power supply systems installed at the Fukushima Daiichi Nuclear Power Plant completely failed to function (an engineering problem).
As a result, a meltdown occurred, and the irreversible situation continues to this day.
I won't go into details, but as you all know, the cause of this accident wasn't solely due to engineering issues.
Some well-known examples include "ignoring previous warnings about problems with multi-layered protection and auxiliary power supply systems," and "inadequate accident procedures and insufficient training." It's still fresh in our memories how mutual checks and balances between companies, the government, the Atomic Energy Commission, and the media were not functioning properly at all, and how poorly the response after the accident was handled.
While it's unlikely that the Fukushima Daiichi Nuclear Power Plant would have remained completely unscathed by that massive tsunami, it's easy to imagine that the outcome would have been quite different if the checks and mutual checks by those involved in the surrounding area, as well as the post-accident response, had been functioning properly.
This scenario is almost identical to the Comet series of crashes, where a failure in oversight by those involved occurred.
UnfortunatelyAs engineers, we not only failed to learn the true lessons from the Comet disaster, but we have also caused an even larger accident.
The true lessonLearning from history and putting it into practice is difficult.
Although this is a mechanical design course, let's take a look at the Comet crash not only from the perspective of the aircraft (hardware) but also from other (software) aspects.
BecauseEngineering ethics play a significant role in the software aspects as well, and the right systems can often prevent accidents even in uncharted territory.
Furthermore, this will undoubtedly have a significant impact on the detection of malfunctions and the design of safety features in electronic control devices, which will become increasingly numerous and complex in the future.
First, as background knowledge for considering the problems, I will briefly explain the timeless way of thinking that applies when venturing into uncharted territory.
How to deal with the unknown
Not limited to mechanical productsTrying something you've never done before (unknown territory) is a wonderful thing.
However, there's a major caveat: the worst-case scenario is that you might not even realize you've stepped into uncharted territory.
I have many thoughts about this situation of not noticing, but for now I will omit the mechanism behind how this situation occurred.
However, just because it's an unknown territory doesn't mean you should grope around cautiously and slowly try things out; that's quite inefficient, and trying things without thinking can be extremely dangerous depending on the situation.
Moreover, both in the past and present, in this economic society, we are subjected to fierce competition, so even in uncharted territory, we must efficiently and quickly conquer it, or we will be left behind by our rivals.
thereTo efficiently conquer uncharted territory, we need to concretize the unknown aspects.We will continue to do so.
Next time, I'll introduce specific methods for tackling uncharted territory.
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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