Systems and their Safety

Almost any piece of engineering is more complicated than it appears to the untutored eye. That is as true of a single component as it is of a complex system.

Whereas the engineer may discover ways for a component not to perform as she designed it, it is also vital that a system be studied with its many components interacting. The engineer may find that, in a system, every component may behave perfectly in itself yet still those components interacting may give problems.

System engineering is is an important subject and many engineers wrestle with and study the performance of complete or partial systems. It is very difficult too.

It is a fact of simple statistics that many components interacting offer many, many possible combinations of ways to go wrong or just not perform as planned. That also means that it is so very easy to imagine what it is that is giving the problem. Beware of getting fixed on such an idea: for it can just as easy for it to be wrong.

The Lad’s car was losing water, but only a certain volume – not all of it. Then there was the strange bubbling in the coolant tank. On hearing this, the garage mechanic said that’s probably a leaking header tank; that model is prone to it. OK, some things now seemed to hang together. The garage ordered a new header tank. Took a few days as it had to come from abroad. That with the labour costs as well took it to about £150. Drove off. System still leaked.

Then we looked – instead of making such an easy, unexamined assumption. It wasn’t the header tank. It was the radiator. Ooooohhh Noooo. Not one our finest moments – not the way an engineer should do it. The seemingly significant point that not all the coolant disappeared – but only a certain amount – was not significant at all. Only a little disappeared because we were checking frequently – it would all go eventually. Radiator replaced and problem solved!

Comet 1 nose
Comet 1 – The face of triumph and tragedy.

 

On a much more serious level but many years ago, was the Comet crash problem. When one crashed losing many lives, they held an enquiry. Wreckage was inaccessible at the bottom of the Mediterranean. The designers developed several ideas for the possible cause and designed ways to put each right. The Abell Committee concluded that:

“Although no definite reason for the accident has been established, modifications are being embodied to cover every possibility that imagination has suggested as a likely cause of the disaster. When these modifications are completed and have been satisfactorily flight tested, the Board sees no reason why passenger services should not be resumed.'”

The Air Safety Board concluded that:

It realises that no cause has yet been found that would satisfactorily account for the Elba disaster…… Nevertheless, the Board realises that everything humanly possible has been done to ensure that the desired standard of safety shall be maintained. This being so, the Board sees no justification for imposing special restrictions on Comet aircraft.

Sixteen days later another Comet crashed in the Mediterranean taking with it all the passengers and crew. There was fatigue failure between two openings in the top of the fuselage that had not been considered.

The authorities did not know what the cause of the first accident was but let the aircraft fly again with passengers. Hindsight is a marvellous thing but The Lad believes that the authorities should only allow an aircraft to fly after a crash

WHEN THEY KNOW THE CAUSE AND THAT THE PROBLEM IS PUT RIGHT

Is this too strong? Do the current Regulators follow this principle?

 

 

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