When will the hydraulic L/R PMP PRESS LO annunicator activate?

The hydraulic L/R PMP PRESS LO annunicator activates when the pressure sensor detects a reading of less than 750 PSI. This alarm is a warning indicator designed to alert the crew that hydraulic pressure is falling below a threshold necessary for proper system operation. Maintaining hydraulic pressure above this level is critical to ensure that hydraulic systems function correctly, which is essential for control surfaces and other systems that rely on hydraulic pressure for operation. The activation at this specific pressure point serves to provide a timely warning, allowing the crew to take appropriate actions to mitigate any potential issues related to low hydraulic pressure.

In contrast, the other options define pressure levels that either do not trigger the alarm or describe conditions that indicate normal or excessive pressure, which would not activate the low pressure warning. For instance, pressures exceeding 1000 PSI indicate a high-pressure scenario, while being at normal pressure would clearly not necessitate any warning indication. Thus, the focus on the critical threshold of 750 PSI is central to understanding the safety and operational protocols involving hydraulic systems.