Originally Posted by
P330
Gas turbine engines are usually started by a high pressure air powered starter motor. The air source may be internal (APU), external (Air Start Unit, e.g. Palouste), cross bleed air from another engine that has already been started by other means or older “exotic “ systems such as Avpin, cartridge or internal air bottles - Lightning, Canberra, Mk2 V Bombers.
What most methods have in common is a system for removing the air supply and disengaging the starter motor when the engine has reached self-sustaining speed. To achieve this an electrical solenoid will shut the start valve when this occurs. Should this solenoid fail it is possible to operate the start valve manually with an appropriate tool; box spanner on an extension bar. To carry out this procedure an engineer plugged in to external intercom is positioned by the engine to be started. At the point in the checklist when Start is selected the engineer is instructed to open the start valve and when the start is complete he closes the valve, secures the access panel and all proceeds as normal.
Clearly this his procedure requires that the ground personnel are qualified and trained which means having an engineer qualified on type. No suitably qualified engineer available then no capability to start the engines. I am not saying that this was the case here, but it seems highly likely as dispatching with an unserviceable air start valve is not unusual.
YS