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

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With regard to a twin spool gas turbine engine, an abortive start (hung start) will result in:

A
N2 speed stabilising at a lower than normal rpm and a subsequent increase in EGT.
B
N2 speed stabilising at a higher than normal rpm and a subsequent increase in EGT.
C
N2 speed stabilising at a higher than normal rpm and a subsequent decrease in EGT.
D
N2 speed stabilising at a lower than normal rpm and a subsequent decrease in EGT.

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 (low N1 and N2 rotation) when 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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