No a 747 does not start on 3 engines. But we are comparing a 747 starting on 3 with a twin. The fact that the quad originally had 4 is not really relevant when it comes to calculating the probability of a future failure.
Even though the thread title is "BA747 3 engine LAX-LHR" some of you seem to have missed that I was considering a
747 on 3, not a 747 on 4, and this has led to some misunderstandings.
Secondly, if what you seem to be trying to argue were to be correct, then a 747 would be more likely to experience two engine failures on a flight than a twin jet would be to experience one. Are you really saying that?
No I did not argue that.
I wrote that, all else being equal, a quad (
that's flying on 3) is 50% more likely to experience 1 engine failure than a twin (on 2).
It's quite straightforward - but
whether this difference is important depends entirely on the consequences of an engine failure in each case.
GGV - I suggest you think about it.
3 engines vs 2 engines
3 engines that can fail vs 2 engines that can fail
An analogy...
3 lottery tickets vs 2 lottery tickets = 50% more lottery tickets
This an extremely basic probability issue - I don't see why people have such trouble grasping it.
All I am suggesting is that before embarking on an extended flight over the North Atlantic it needs to be
considered that the quad (
on 3 engines) is 50% more likely to experience an IFSD than a twin on 2. This is
just one factor to be considered - there are of course many others.