To start the engines a sequence of events is required to allow fuel flow, to rotate the engine and to provide ignition energy.
During the starting cycle the engine needs to be rotated until the fuel has ignited and the temperature of combustion is sufficient for the engine to rotate without assistance.
At this point the engine is said to be self-sustaining. This is a device which converts the presumed air energy to a rotating motion.
The starter rotates the accessory gear box and gear box rotates the HP compressor shaft (N2). The most common method in modern use is to use an external air source or an internal auxiliary power unit to start the first engine, and to cross drive start the remaining engines. Some smaller engines and the B787 make use of a electrical engine start.
Air at high pressure can be provided by an external air compressor trolley connected to the engine by ground crew or by the onboard APU.
Author – Mohamed Freihat
(C130/L100 , A&C approved consultant)