Question: Engines have been used for 50 years and there is no obvious evidence showing that they are not safe How could you come up with this idea

Katy Milne answered on 15 Mar 2010:

I was a bit unsure exactly what your question is but I am going to try and give an answer. If it is the wrong thing, let me know.

Jet engines have been around for longer than 50 years. The earliest attempts were at the beginning of the 20th century – 100 years ago! There are other types of engine that have been around for even longer: like the steam engine and the internal combustion engine. Jet engines are, in some ways, alot simpler than the internal combustion engine (the one in your car). The science for a jet engine is quite easy: the air is sucked in and heated up. The heating causes it to expand and it is forced out the back at very high velocity. This ‘jet’ of high velocity air provides the forward thrust. All of these processes are happening at the same time and continuously. In a car engine, each process happens one after the other and only one part of the cycle – the part where the gas expands – creates energy to move the car forward. However, the jet engine is not the simplest engine, as it still has moving parts. The simplest engine is the ramjet:

http://en.wikipedia.org/wiki/Ramjet

All engines can break. However, because jet engines are mainly used on aeroplanes they have to work otherwise the plane could crash. Jet engine designers have to get it ‘right first time’. Aerspace is called a ‘right first time’ industry. There have been examples where the engine has failed however, the likelihood of failure is very small compared to that of any other kind of engine. The industry often quotes the figure: ‘deaths per number of kilometres travelled’. For cars, 3.1 people die for every billion kilometres travelled. For aeroplanes, 0.05 people die for every billion kilometres travelled. However, not all of those 0.05deaths per billion kilometres are caused by engine failure. See http://en.wikipedia.org/wiki/Air_safety

Jet engines are so safe partly because we design and build them carefully and partly because of inspection. My team and I inspect all the parts that go into a jet engine before it is assembled to make sure they are perfect. The parts have to be the right size and shape. The parts must not have surface damage (such as marks or cracks). The material that we use to make the parts must be very pure so that it behaves exactly how we expect. Our inspection makes sure of this and so helps make sure engines are safe. Eventually, with continued use, all jet engines will break. We only allow the jet engines to fly for a certain amount of time before the components inside have to be replaced – making them even safer. We use inspection to check whether parts need to be replaced. I hope that answers your question, but let me know if not.