According to a particular AFM, takeoff derate settings are time-limited to 5 minutes. Is it possible that MCT or climb thrust is actually a higher thrust setting?
Two things confused here.
- The 5 minute (or 10 if purchased as described above) limitation applies to FULL TO thrust. The 5 minute limitation must be observed in all takeoffs due to fact one can select full power in some scenarios.
- Any derated/assumed takeoff settings are engine thrust reduction techniques, so hence it is possible that the MCT is higher than your TO thrust used, but only in those cases where used.
It cannot be overemphasised that the limitation is applicable to FULL TO thrust.
Any reductions to that FULL TO thrust are saving your engine working too hard for too long, enhancing its lifecycle.
Finally, if you experience an engine failure, flying an engine out procedure, remember this is procedure designed to take into account the limitation as above, either 5 or 10 as purchased.
This thus requires crew to be aware of the time after which (even if not yet having completed the escape manoeuvre) to select MCT. Many crew in the simulator are oblivious to this fact as they tend to practise EO which achieves Flap Up selection and MCT selection within 5 minutes. When faced with the time limitation (due required turns, very heavy weight, a higher MFRA than standard, etc), many crew forget the time limitation and it becomes a nice discussion point afterwards.