4 thoughts on “How far can a 747-400 fly with three engines, and can it sustain its cruising altitude?

  1. Fly B

    Not sure about keeping it’s original cruise altitude, but certainly high enough to not lose efficiency over having to fly lower. Maybe from 36,000 to 30,000 as a possibility.

    On three engines it will certainly be able to continue on to its destination, or at the very least be able to find a safe place to land.

    There are many articles actually about 747s losing a single engine on take-off and electing to continue.

    http://www.flyer.co.uk/news/newsfeed.php?artnum=173

    That’s a news article on a plane losing an engine on take-off, then choosing to fly 11 hours to London on three engines rather than returning to its point of departure for an inspection.

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  2. stinkbad

    Yes, the flight would not be dispatched unless it would be able to do so under most commercial regulations. I am not sure how or if much efficiency is lost due to the loss of one engine. I am sure there is some efficiency lost due to the flight control deflections needed to keep the aircraft in control as well as the slow(er) spinning fans creating drag instead of thrust.

    Depending on the 4 engine operating cruise altitude depends if/and how far it would drift down on its 3 engine altitude, but probably not very much lower.

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  3. Caretaker

    A Flight Plan with parameters of maximum weight and fuels required would consider flying to a mid way point, losing one engine, and still be able to reach the destination with required fuel reserve. If you lose the engine before the mid way point (point of no return) you turn back. If later, you proceed to your destination.

    It takes a certain amount of thrust to achieve a specific altitude. If you lose one engine you lose the ability to efficiently maintain the same altitude. At the same time the dead engine increases drag. To conserve fuel the aircraft will normally descend to an altitude where thrust available, from three engines, is still efficient

    One of the Flight Engineer’s duties was to calculate optimum three engine altitude through the flight. As weight decreased, due to fuel burn off the three engine altitude would increase.

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  4. John R

    A British Airways 747 lost an engine shortly after takeoff from the US west coast, and the pilot and company dispatch elected to continue to London instead of returning their originating airport. Not only can it sustain cruising altitude, it can usually climb to cruising altitude with 3 turning.

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