What is the ITT redline during startup?

• A. 350°C
• B. 450°C
• C. 550°C
• D. 600°C

Answer: (B)

During startup, the engine is particularly vulnerable to thermal stress as fuel is introduced and the rotor is accelerating from idle. The Inter-Turbine Temperature (ITT) redline sets the maximum core temperature the engine can safely reach during this unstable phase. A startup limit of 450°C is chosen because it is high enough to allow ignition and spooling, yet low enough to protect turbine blades, bearings, and other hot sections from excessive heat if the start is not progressing smoothly. If ITT approaches or hits this redline, you would follow the start procedure to reduce fuel, allow the temperature to fall, and possibly abort the start to prevent damage. Once light-off is established and the engine is stabilizing, ITT limits can be raised toward the normal operating maximum.

Why not a lower or higher value? A lower number would make starts too fragile, causing unnecessary aborts, while a higher number would risk overheating the turbine during the critical start-to-sustained operation transition.