I'm curious about this--wouldn't one expect more engines to be safer?
Unless having more engines increases the chance of certain kinds of accidents? Like maybe the chance of an engine failure damaging the hull goes up with more engines?
Not questioning the justification--I do believe it--I'm just curious about the details.
All else being equal, potentially - although as I mentioned there have been cases where one engine falling off a 4 engine aircraft hit another in the process. But ETOPS certification is based on it being demonstrated that engines are sufficiently reliable that the probability of an independent failure is incredibly unlikely, and also requires that operators have a stricter maintenance process. The only dual engine failures on modern two-engine aircraft I can think of off-hand have been fuel exhaustion (either actually being out of fuel, or ice blocking fuel filters in the case of BA38), and would have affected 4-engine aircraft just as badly.
There's US1549 and FR4102 - are there any others? But yes, the assumption about failures being independent is obviously violated by large flocks of birds, although this has also resulted in the loss of 4-engined aircraft.
Engine failure is very dangerous. 4 engines are twice as likely to have a major failure than 2.
(despite having "fuses" so an engine can depart without taking much of the wing with it, there are many cases of single engine failure bringing down the airplane)
Unless having more engines increases the chance of certain kinds of accidents? Like maybe the chance of an engine failure damaging the hull goes up with more engines?
Not questioning the justification--I do believe it--I'm just curious about the details.