During the start of an ATM, what is the time limit for hydraulic pressure to reach the operating range?

During the start of an ATM (Auxiliary Power Unit), it is critical for the hydraulic pressure to reach the operating range within a specific time frame to ensure the proper functioning of the aircraft's hydraulic systems. The correct answer indicates that the time limit is 15 seconds. This time limit is in place to ensure that the hydraulic system is ready to perform essential functions such as moving flight control surfaces and operating landing gear, among other critical tasks.

If the hydraulic pressure does not reach the operational level within this specified time, it may suggest issues with the hydraulic system or the APU itself, which could compromise the safety and reliability of the aircraft’s systems. Adhering to this 15-second limit is important for operational efficiency and safety.