Old King Coal
Are you following Boeing procedures or are you following your own invented "I have no patience" approach?
If you follow Boeing guidelines you should be just fine with the autothrottle. Set the engines to approximately 40% N1, let them stabilise, and then hit the TOGA button. Too many times you see crews failing to nail a simple request like "approximately 40%", will not wait for the engines to react and push even more forward asking 60-70%. That same "no patience" approach will prevent the pilot from allowing the engines to stabilise a second time, so they go on and hit the TOGA anyway while the engines are reving up with sometimes more than 10% N1 difference. Now that's going to be some fine dancing there. But that's not the autothrottle. That's the pilot's fault not understanding how a HBPR turbofan works.
The same happens when the engines approach target N1 for takeoff. The autothrottle slows down approaching the target N1, then the finetuning begins. When the autothrottle slows down the acceleration, too many pilots are trigger happy to intervene and push the throttles forward leading to overboosts from which now the autothrottle has to correct again.
In cruise the limits are clearly defined and not that big of an issue. There is a max throttle position discrepancy allowed, not an N1 difference. And the autothrottle manages that throttle position discrepancy a lot more/better than many pilots...
And the same happens when coming out of an idle descent. No patience, no idea of how a turbofan works close to idle, and overcorrecting before having to reduce power again.
Between 40%N1 and TOGA/assumed power, the autothrottle should work fine in 98% of the cases. If not, you should talk to your maintenance because these are limitations.
Last edited by BraceBrace; 18th Jan 2021 at 13:36.