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What happens when you apply full throttle to the engines of a Boeing 787 at cruise altitude for 5-10 minutes?

Other than wasting fuel, what maximum speeds are reached?

Does that pose any danger or damage to the airframe?

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Autopilot flying straight and level

Upon reaching the VMO/MMO the A/P will be inhibited from trimming down any further, which will result in the airplane climbing at the VMO/MMO.

Overspeed protection limits the speed to which the airplane can be trimmed. At VMO/MMO, the trim reference speed is limited by inhibiting trim in the nose down direction.

Hand flying straight and level

Pushing the thrust levers forward will result in a climb at the current speed due to the fly-by-wire design—only the trim buttons change the "trim reference speed".

Once the column forces are trimmed to zero, the airplane maintains a constant speed with no column inputs. Thrust changes result in a relatively constant indicated airspeed climb or descent.


Source: Boeing 787 FCOM chapters 4 and 9.

Further reading:

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    $\begingroup$ So basically setting full thrust will put you in the coffin corner eventually rather than overspeeding? Interesting choice. $\endgroup$ – Sanchises Mar 11 '18 at 21:10
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    $\begingroup$ @Sanchises - Sure, if the crew want to ignore the caution light, the beeper, the autopilot EICAS message, and not having pitch command bars :) $\endgroup$ – ymb1 Mar 12 '18 at 11:02
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    $\begingroup$ You could hold a forward input on the control column to speed up beyond VMO/MMO instead of having the aircraft climb with zero control column force. $\endgroup$ – Cpt Reynolds Mar 12 '18 at 17:00

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