What is the maximum duration for the transient EGT between 715°C and 824°C during APU start?

The correct answer is based on operational protocols established for the Auxiliary Power Unit (APU) during start-up procedures. The transient Exhaust Gas Temperature (EGT) limit between 715°C and 824°C is specifically defined to ensure the safety and integrity of the engine.

During start-up, the APU is subject to a variety of thermal and operational stresses. The maximum duration of 20 seconds for transient EGT between the specified temperatures allows sufficient time for the APU to stabilize while still safeguarding against potential overheating or damage to the engine components. This limit is designed to mitigate risks associated with prolonged exposure to elevated temperatures, which could lead to accelerated wear or malfunction.

Understanding this requirement is critical for maintaining APU operational standards and ensuring safety during aircraft operations.