How far can a twin-engine plane fly on one engine?

On June 25 one of the engines failed on an AirAsia X flight 90 minutes into its flight from Perth to Kuala Lumpur. The aircraft returned to Perth on one engine and while the Airbus A330 landed safely, passengers were left shaken by their ordeal.

Many airlines prefer twin engine aircraft due to their low operating cost, and frightening as losing an engine might seem, there is a generous safety margin on all twin-engine aircraft.

As a requirement for certification, an aircraft must be able to take off and climb out of a missed approach with flaps fully extended on the power of a single engine alone. It must also be able to cruise for an extended period.

All twin-engine aircraft have an extended twin-engine operations (ETOPS) rating. This is the time a particular aircraft type is certified to continue flying with one engine out.

A long ETOPS rating gives an aircraft a big commercial advantage since it allows them to operate on long trans-oceanic routes, far from airports to which they could divert in an emergency.

The Boeing 787 Dreamliner has an ETOPS rating of 330 minutes. The Airbus A350-900 has an even longer ETOPS rating of 370 minutes, more than six hours, which Airbus says allows it to operate up to 4630 kilometres from the nearest airport.

This means the A350-900 can operate over any route since there is nowhere on the planet further than that from the nearest commercial airport.

See also: Airbus A350 vs the Dreamliner: Which new plane is best on a long haul?

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