What could result if an ENGINE SHUT OFF is placed to on prior to 18% N2?

Placing the ENGINE SHUT OFF to the "on" position prior to 18% N2 can lead to a hot or hung start because at this stage, the engine is still in the initial phases of the start sequence where proper airflow and fuel classic conditions have not been established. If fuel is introduced prematurely by activating the shutoff, the fuel may ignite before the engine reaches optimal speeds, leading to excessive temperatures (hot start) or insufficient acceleration (hung start).

Understanding engine operations is crucial, particularly how N2 (the high-pressure compressor speed) relates to airflow and combustion stability. If insufficient N2 has been achieved, the engine may not be ready to combust the fuel efficiently, leading to abnormal operating conditions that compromise engine safety and performance.