Re: 2 Vs 4 engines - CFM56 Engineering Dept Costs

Date:         17 Dec 99 01:57:44 
From:         Erik Verheijden <>
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> Perversely, a 4 engine aircraft is less likely to get you where you are
> going than a 2 engine most of the time. Engine failure is more likely on
> a 4 engine aircraft because there are more engines (D10's have to turn
> back because of engine failures less often than 747's, even though 747
> engines are more reliable, the problem is the 747 engine needs to be at
> least 33% more reliable)...

I couldn't agree more. It seems like abusing statistics when stating
that a 4 engine a/c has twice the chance of an engine failure that a two
engine a/c has.

A closer look at statistics tells us that of all recent
incidents/accidents to large airliners, the number of engines on the a/c
wouldn't have made a difference in a single case.

Safety in a/c design is all about statistics. A mishap is allowed every
couple of million flight hours. Adding engines (why not use 6 to be on
the safe side?) does not affect the rate at which break-ups, fires and
decompressions occur. Those statistics involve to many factors to simply
improve by adding engines.

Erik Verheijden.