Posted: Oct 07, 2017 5:13 am
Having four engines over water used to be a good rule back when engine failures were relatively common, but it's considered extremely unlikely that an aircraft would have two fail in flight nowadays. Most large twinjets are certified to fly for three hours on a single engine to a contingency airport, if need be, and that's enough to take them pretty much anywhere on the planet.
If an aircraft has four engines it's almost certainly because they don't make engines big enough for it to be able to take off with just one of them operating, which is a requirement for twinjets. The tipping point is when you get to a max take-off weight of around 360 tons, although it's creeping upwards as more powerful engines are built.
If an aircraft has four engines it's almost certainly because they don't make engines big enough for it to be able to take off with just one of them operating, which is a requirement for twinjets. The tipping point is when you get to a max take-off weight of around 360 tons, although it's creeping upwards as more powerful engines are built.