Originally Posted by A4
What's the spool time from idle on 777 compared to the A320? Does the 777 have "approach idle"?
The regulation is the same for all Transport Category airplanes.
FAR 25.119 Landing Climb: all-engines-operating specifies "The engines at the power or thrust that is available 8 seconds after initiation of movement of he power or thrust controls from the minimum flight idle to the go-around power or thrust setting", The airplane manufacturer selects the flight idle setting so that it meets that requirement.
Typically on high bypass-ratio engines during the first 3 or 4 seconds the acceleration is mostly in the high-pressure part of the engine with little increase in thrust.