Extended Twin Operations. A set of regulations that imply that two-engined airlines can fly long sectors where no diversion airport is close. (like over-water sections).
A nice explantion is here: http://gc.kls2.com/faq.html#$etops
I rmember having read somewhere, that ETOPS is not really about reduced aircraft range because of the lack of one engine, but differently.
An airliner like a 767 or 777 could easily fly transatlantic sectors on only one engine. It is powerfull enough for it, the engines are only working on a small percentage of their power anyways. One GE90-90 engine as featured in the 777-200ER can provide almost as much power as 3 A340 engines. So that is not the problem.
However, the compressor for cabin presurization is directly connected to the engines. There is a compressor on both engines. When one engine is out, that compressor won't work anymore and you have lost your redundancy.
The reliability of those compressors is lower than that of the engine. As the risk is too high to fly at 30.000+ ft and then losing cabin pressurization, the airliner will have to lower altitude. And as the air is thicker at lower altitudes, the engine needs a lot more power to fly, and so the range is being drasticly reduced.
I can't find the source of this anymore so I have no clue if it is true or a hoax. Is there any expert here?
[Edited 2005-06-25 13:40:30]