If the EHYD PX LO illuminates, which aircraft devices are likely inoperative?

When the EHYD PX LO warning illuminates, it indicates that there is a low hydraulic pressure condition in the aircraft's emergency hydraulic system. This system is crucial for operating specific emergency functions, namely the emergency landing gear and flap extension. Under these circumstances, the hydraulic pressure necessary for deploying the landing gear and flaps may not be sufficient, rendering these devices inoperative.

The emergency landing gear must be deployed manually in the event of a hydraulic failure, and if the hydraulic pressure is critically low, this process may be compromised. Similarly, the flap system, which relies on hydraulic pressure to function, is also affected, making it crucial to address this warning promptly.

In contrast, the other options involve systems that would not directly correlate with the EHYD PX LO warning. For example, autopilot and engine throttles are functions that rely more on electrical and mechanical controls, while primary flight displays and altimeters are related to avionics that don't depend on the emergency hydraulic system. Navigation systems and communication radios operate independently of hydraulic systems as well, making them unaffected by a low hydraulic pressure condition. Understanding these relationships highlights the importance of responding to the EHYD PX LO indication by prioritizing emergency hydraulic system checks and ensuring safe aircraft operation.