Re: Engine failure and ETOPS

From:         Pete Mellor <>
Date:         24 Aug 94 14:02:00 
References:   1
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  or MIME structure (Victor A. Carreno) on 21 Aug 94 15:35:10 calculates 
the probability of loss of hull due to two engines out independently on a 
twin-jet (with GE CF6-80C2 engines) as:- 

> 2.88 x 10^(-10) probability of airplane loss per flight

This is very much better than the certified probability of losing both 
engines, which is 10^(-9) per flight hour, as with other critical systems. 

The point of the 10^(-9) figure is that, given 100 critical systems on 
board (pessimistic) the probability of hull loss due to failure of any 
critical system should be no more than 10^(-7) per flight hour, which is 
*roughly* the actual rate for hull loss *due to all system causes*. 

It would be interesting to see the actual rate of hull loss *due to 
engine failure* for comparison. I would assume that, in compiling such 
statistics, manufacturers would omit accidents due to environmental 
factors, e.g., bird-strike or flying over active volcanoes. 

Peter Mellor, Centre for Software Reliability, 
City University, Northampton Square, London EC1V 0HB 
Tel: +44 (71) 477-8422, Fax.: +44 (71) 477-8585, 
E-mail (JANET):