021 - Airframe, Systems, Electrics, Power Plant ATPL(A) (EASA 2016)

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A hung (abortive) start of a gas turbine engine may be caused by…

A
compressor surging.
B
the starter cutting out early in the starting sequence before the engine has accelerated to the required rpm for ignition.
C
a too low pneumatic starter pressure.
D
failure of the fuel to ignite in the starting sequence after the engine has been accelerated to the required rpm by the starter.

Hung start - will result in N2 speed stabilizing at a lower than normal rpm and a subsequent increase in EGT. The engine fails to accelerate sufficiently because of a too low pneumatic starter pressure before the fuel is supplied to sustain combustion. Upon recognition of the hung start conditions, the flight crew needs to shut down the engine, conduct a cranking and initiate a cooling sequence before attempting a new engine start.
Hot start – usually caused by an early starter cut-out, fuel mis-scheduling (leading to excess fuel in the combustor), or strong tailwinds. Intermittent light-up at very low rpm (sub-idle) will be observed, followed by a very sudden increase in EGT. That’s why EGT monitoring is one of the most important parameters to monitor during the engine start sequence, which will allow you to abort the start immediately.
Dry start – fuel fails to be delivered to the engine and light-up will not take place. The compressor will only reach a given RPM (rather low) because it will be driven only by the starter motor.

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