While we draw comparisons between the 777 & the A340, has anyone noticed that in one respect with engines the two are similar.
Both aircraft have engines which are stretched to their maximum (well, there abouts, the 777 is pretty damned powerful at its current state) - we've had the 777 engine problems & the A340 engine problems.
Noticed that the A340s CFM56s are basically as boosted up as they can be, IIRC SQ was having some problems with their CFM56s after a while (on a plane like the 343E you would need ever bit of thrust you could get - they even had a 4% "Thrust Bump" added.
Back to the 2 vs 4 engine subject, 2 engines are not as bad as you would think. Their shortcomings are that over long water routes you have to follow ETOPS and in some cases that may result in having a route longer than optimal (given that you have to be within 180mins flying time of the nearest airport) and their perceived shortfall in safety over quad engined craft.
However 2 engine craft have the advantage of having extra power for normal circumstances and this is illustrated best by the superior climb characteristics of the 777 over the A340. ETOPS aircraft also have stricter maintenance schedules and thus tend to be more reliable (regulations stipulate this).
A twin engined craft on one engine should have as much power as a quad engined craft on 3 engines. Climb performance requirements are the same regardless of the amount of engines, so in the respect of losing an engine on takeoff a twin engined craft is just as safe as a quad engined one - and safer in NORMAL circumstances (normal being where you have all engines)
Engine failures/shutdowns are few. In the modern era, there has never been an aircraft accident due to a loss of thrust during cruise and there has never been an incident where an ETOPS aircraft lost both engines. A pointer to the fact that more engines doesn't give you more security is the Eastern L1011 incident, where it almost ditched in water off of Miami due to related engine problems with all 3 engines (which would not have happened if the aircraft was operated under ETOPS rules) & if it was a 777. ETOPS rules provide strict limits on the operation of aircraft, which further your safety. They are actually equipped for ditching (which has never happened) & have more safety systems over their quad engined friends.
As a twin jet is "overpowered" the engines can be derated further on takeoff, while still providing a sufficient safety margin, saving the engine wear & tear. Quad engined craft require high power settings.
Because of a twin jet's better power characteristics, a twin jet is safer in other trying circumstances; it will cope better in windshear, be able to perform GPWS escape manourvres better, be able to perform go arounds better, not to mention climb better in normal circumstances. So in the bulk of safety situations a twin will actually be safer.
If you want to talk about losing engines, worst case scenario is losing two engines on a quad, so people ask what happens if you lose two on a twin? Actually, if we look at the incidents with quad engined craft losing two engines, such as the United 747 at Honolulu and the ElAl 747 at Amsterdam, we see some thing else.
The engine failures were related, in the UA plane debris from the fuselage caused both engines on the same side to fail, in the ElAl incident, the explosion of one engine caused the other to fail.
But, has the plane been a twin jet, you would have only lost one engine. And to look at numbers, a twin jet would have 100% of its engine out performance, but the quad jet - only 67% of required engine out (FAIL)performance (I know which one I'd want to be on). Had these events occurred closer to the ground, a crash could be quite possible in a quad jet; they would not be able to meet minimum climb requirements.
You see, ETOPS is quite good in the sense that it is a lot safer. Because the regulators believe that quad jets are immune from problems related to engine failure, they can fly anywhere (within reason), where as twin jets have to be within 3 hrs flying time from an alternate. But isn't that better, twin jets comfortably fly on one engine (they're designed to), but if you're in a quad jet, who knows how bloody far you could be from an alternate - that's more important. And ETOPS stipulates that the alternates have to be available (ie weather issues), whereas with a quad jet, you have no guarantee about the availability of your alternate.
For example, what if you have a fire on board. It doesn't matter how many engines you have, but how close you are to an alternate might help.
Twin jets are much better equipped to survive windshear & CFIT situations, two leading accident causes in recent years. Unrelated, total engine failures are not leading causes, in fact are unheard of in modern times. ETOPS aircraft are better equipped for related engine failures than quad jets.
So to summarise, twins are safer under NORMAL circumstances, under ENGINE OUT circumstances - they're bloody safer than you think!
That's why, I feel just as safe boarding a 777 over an A340, a B767 over B747 (heck, maybe safer, mind you I don't care, given that I fly Ansett). So, if you're still not convinced, let me ask you one question.
"Has there ever been an incident involving an ETOPS aircraft where the aircraft has lost both engines in unrelated cirucumstances?"
The A340 is quieter than the 777 and its cabin layout is quite good (never more than 1 seat away from a row) and good in the sense that you can't squeeze extra rows in, ala 777 - 9 abreast vs 10 abreast. From a pilots perspective it's a great plane, apart from the power. Some like it, dont mind it, some wish it had a bit more grunt. At lower weights, it would be quite good. The difference between the 777 and the A340 is that the A340 is almost more exclusively used on long haul routes, where as the 777 is quite likely to be found doing regional routes as well. You won't find many A340s doign 1-2hr hops, that's why we have the A330. And I'll point out that comparisons between the A330 & B777 may also be invalidated by the fact that the A333 is a real short haul aircraft, like it or not and that is reflected in the way airlines configure them.
And in all the light of this, I'm actually divided between the A340 & the B777 - they both have their good points.
I'm sorry if this has been long, but at least you'll probably have learnt something.
PS: NO, I do not advocate single engined craft.