Quote:
Originally Posted by kknudson
FAA rules used to require > 2 engines for over water flights, incase one failed.
With newer more powerful engines, 2 engine planes are now certified for over water flights.
Even older 737s with newer engines are now used over water too.
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The L-1011 and DC-10 used three engines to achieve a longer ETOPS (Engines Turn Or Passengers Swim) and thus able to cover long distance routes over water without stops with the then-current engine technology.
The B727 was a compromise a/c designed to fill the multiple needs of airlines for short runway capability, high altitude runway capability and ETOPS.
Newer engines have been certified for longer ETOPS so an extra engine is redundant nowadays. Engines are significantly more powerful now as well.