When must the fuel be shut off during the start sequence?

The fuel must be shut off during the start sequence when the Interstage Turbine Temperature (ITT) exceeds the temperature limit. This is a critical action intended to protect the engine from overheating and potential damage. During the start sequence, the ITT is monitored closely, as excessive temperatures can indicate problems such as a rich fuel mixture, inadequate airflow, or other malfunctions. Shutting off the fuel helps prevent further temperature rise that could lead to engine damage or failure.

Monitoring ITT is a standard operating procedure during engine start and is vital for ensuring the safety and integrity of the engine. If the temperature exceeds specified limits, taking immediate action by shutting off the fuel is essential to mitigate risks associated with overheating.