To: Juliet November
The calculated failure probability of 1 10-9 is for catastrophic failure where the engine sheds some high speed rotating parts and could possibly down the aircraft or cause passenger or crew death. The actual probability of failure or reliability number for the engine is quite a bit lower that 1 10-9 probably around 1 10-6.
These failures are not for a single engine it is for all engines of that type. It doesn’t take a very long time to accumulate 1000,000 hours of total engine operating hours. Let’s say there are 1000 737s that have the same type of engine. If all 1000 aircraft flew for 2000 hours in one year you would accumulate 4,000,000 operating hours and from a statistical standpoint you would expect to have 4 engines fail for any reason that caused loss of the engine function.
The engine on the 737 has already experienced a catastrophic failure at Manchester so, from a statistical point of view you should not experience another catastrophic failure in the life of the 737.
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The Cat