Crossfeed Start

Actually, it's called a cross bleed start. Jet engines are normally started by air pressure from the APU. If the APU is inoperative, one engine is started at the gate utilizing a GPU. The remaining engine(s) are started using the the air pressure of the operating engine(bleed air from the cross side). This engine must be set to certain thrust level to ensure enough air pressure for engine start. This level is above idle and can cause damage to other aircraft or equipment that are too close to the rear of the aircraft.