Tue Oct 26, 1999 9:48 am
Let me explain something to you about ETOPS. To get 180 minutes ETOPS an airplane fleet MUST show that an engine shuts down only ONCE for every 50,000 flying hours. Over the life time of an airframe, then - about 100,000 hours, any one airplane can be expected to have just TWO engine shutdowns.
These two engine shutdowns MUST occur within 180 minutes of each other in a 100,000 hour lifetime. The chance of that happening is 6x10(-10) or 0.000000006%. Having said this, that is still a statistical chance. This is because in the real world accidents and random events do infact occur.
If the 1 in 60 billion chance that a dual engine failure will happen to an ETOPS rated twinjet it will not end ETOPS. ETOPS is what is known as an "acceptable risk" and even in the event of an airliner losing both engines due to mechanical failure it will not be removed as a system of operation. Needless to say there are some ETOPS measures that should be applied to ALL aircraft because it increases not only safety, but also the economic viability of operation.
Now, because ETOPS is a system of operation there may be, even in our lifetimes, an event where something goes wrong. To show you how rare that will be is to say this: there has been 1.3 million ETOPS flights in the last 15 years. The chance of a dual IFSD on a 180 minutes ETOPS rated twinjet is 1 in 60 BILLION. Therefore, after 60,000 times the last 15 years only ONE dual IFSD will occur.
Meantime, the chance of you falling out of the sky in a quadjet due to ALL FOUR ENGINES failing - at current reliability rates for quadjets - is 1 in 30 BILLION. You are, therefore, and in theory, twice as safe on a twinjet.
Besides, all engines failing on an airplane DOES NOT MEAN DEATH. It means a crash landing. Probably overwater - therefore a ditching. There is absolutely no reason why the passengers and crew of a ditching airplane CANNOT survive the ditch.
Gliding into a mountain, on the other hand, would not be ideal! :-)