The procedure says to descend to lrc ceiling. But, why do we need to descend?

The aircraft is still able to maintain speed even at higher altitudes, at FL300, in FS2020, it was maintaining around 215-225 knots speed with N1 around 89 percent. When I descended to FL150, though it is able to maintain 300 knots, power is still around same.

So why descend?

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    $\begingroup$ What do the real world performance charts say? Maybe the A320 in the flight simulator does not have accurate performance (especially in non-normal situations). $\endgroup$
    – Bianfable
    Jan 21, 2023 at 14:13
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    $\begingroup$ An Airbus can not maintain FL300 on one engine. Your simulation might be flawed, but my guess is you didn’t wait long enough for the airspeed to decrease. If you did, you would probably find the max altitude on one engine would be about FL200. $\endgroup$ Jan 21, 2023 at 14:41
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    $\begingroup$ If you are flying ETOPS and over the middle of the pacific ocean you will need (and your flight planning requirements demand) that you descend to an altitude that will provide the best range/fuel performance (which would be well below FL300). If you are flying over the Himalayas and need to remain above a particular altitude for a while you would "drift down" to an altitude which will allow (hopefully) terrain clearance. So, the performance requirements after an engine failure depend on what circumstance you find yourself in. It's not all about staying as high as possible. $\endgroup$
    – user22445
    Jan 21, 2023 at 16:11
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    $\begingroup$ FenixSim is WRONG. A real Airbus A320 can NOT maintain FL300 on one engine. That is the reason for the descent. $\endgroup$ Jan 21, 2023 at 22:32
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    $\begingroup$ @quietflyer the most efficient single engine descent is included in QRH performance data and is called "driftdown" speed. Driftdown is basically max L/D with one engine inop and the other at max cont thrust. $\endgroup$
    – John K
    Jan 22, 2023 at 3:17

1 Answer 1


Your simulation is almost certainly flawed. For example, an Airbus A320 that loses an engine at Fl330 must descend. There is the single-engine ceiling at which a plane can maintain speed and altitude efficiently. If you want to maintain altitude, then you must sacrifice speed. If you want to maintain speed, then you must sacrifice altitude. If you want to do both simultaneously, descend.

Summarised from here: Mentour Pilot's video on this topic


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