Originally Posted by
tonywestsider
What many airlines do now after pushback from the stand is to start with one engine, power out and taxi then start the rest of the engines while taxiing close to takeoff position in order to save fuel.
Likewise, they may power off one engine after landing and taxi to the terminal on one engine.
This, BTW, is the source of the loud "barking" noise on Airbus jets. When running on one engine, a transfer pump runs to keep the hydraulic system powered by the inactive engine pressurized. This pump makes a heck of a racket.