Hamlet69: I can see where you're coming from. OTOH, a nightmare of mine is being in the middle of the Pacific, 3-4 hours away from the nearest diversion field, and having a fire break out in the cargo hold, or a problem in the fuel system, and knowing that the quad I'm on (be it 747, A340, etc.) does not have as many redundancies or as much fire suppression as the twin I could be flying on that has such systems because of ETOPS.
Question is, are the 340s and 747s really still that far behind the ETOPS-certified twins as they might have been at the beginning of the ETOPS initiative? I wouldn´t be too surprised if most of the ETOPS improvements had come to the quads as well.
Hamlet69: Leaving these "scare stories" aside, there's also the statistical fact that tri- and quad-jets have more instances of diversions that ETOPS-qualified twins, which increases the chance you'll be delayed in getting to your destination.
Diversions and all-engine-out scenarios are two very different
The diversion rate
depends (among other things) on the combined probability of a failure in at least one
of the engines. Which is almost (but not exactly) double that of a twin for a quad, statistically (based on identical individual failure rates). As far as I know (and as I understand Cx_flyboys interesting information above), the diversion decision is taken still more
conservatively for a twin ("always
divert" as opposed to "maybe
divert" for a quad) so the factor might shrink a bit more; But still, the diversion rate remains higher for a quad.
A catastrophic failure
, however, is a completely different type of event
(still only thinking of inflight engine shutdowns). Thank god that we don´t have any actual experience with that (as far as I know), but in this case, the probability of all engines of a quad shutting down independently is by a very large factor
more improbable than for a twin (which is still almost astronomically small). In the simplest theoretical model, it´s the twin´s all-engine-out probability squared
. Of course
ETOPS twins are very safe
. I´ve flown on them on transatlantic routes and I wouldn´t really lose sleep over doing it again. I would just say that a quad that´s built and maintained to a comparable standard will still be safer
- even if it may be slightly more inconvenient
due to a somewhat higher diversion probability. Which is not a contradiction, as much as it might appear to be on first glance. Statistic math is like that.
Hamlet69: Honestly, though, bad maintenance records does not mean that it will affect the airline's bottom line.
Probably not if the difference is marginal
. It may be just me, but when I hear "nightmarish" I think of extra shifts, inexplicable and repeated failures in all areas and, more importantly, delayed or cancelled flights and missed connections. We don´t need to get all religious about it; But "nightmarish" is a pretty strong word, when out of context. It´s basically the last stop short of "won´t work at all under any circumstance" as far as maintenance goes... No way of making money that way...
Hamlet69: Very true. However, he did not state "I believe Airbuses are costing alot in maintence," he said, "they are." Therefore, you are calling him a liar.
If I do actually suspect someone of evil intent, trust me in saying it aloud
. And since I explicitly rejected
your allegation to that effect, you can rest assured that I meant precisely what I wrote. Sorry, no flame war here.