In what scenario should the fuel flow be interrupted immediately during startup?

Interruption of fuel flow during startup is crucial for ensuring safety and preventing potential damage to the engine. The most immediate scenario that requires such action is when the engine fails to ignite.

In the event of ignition failure, continuing to supply fuel can lead to an accumulation of unburned fuel, which can create a fire hazard or cause the engine to flood. Igniting fuel in a non-combusting state can result in excessive raw fuel entering the combustion chamber, potentially leading to catastrophic failures such as an explosion or flameout if sparks were to ignite it.

While other scenarios like exceeding RPM limits, high temperatures, or abnormal noises may indicate issues that require attention, they do not present the same immediate risk of fire or critical damage associated with fuel flow. Therefore, prompt interruption of fuel flow upon ignition failure is critical to maintaining operational safety and integrity of the turbine engine during startup.