Just an SLF here but I heard an "expert" (name of Gleave, Grieve???) on the BBC saying (something like) "we've all been on an aircraft and you hear the engines power up a bit before going to full power to take-off - that's the pilots testing they're going to respond correctly before commencing take-off"
Is that correct?
I always thought it was to do with running the engines up gently to avoid excessive wear by "firewalling" them.
But I'm a retired lawyer so what do I know? Please correct me as necessary. Thanks.