When does the FUEL PX (red) light illuminate?

The FUEL PX (red) light illuminates when the fuel pressurization drops below a critical threshold that indicates a potential issue in the fuel supply system. The correct answer indicates that this light activates at a pressure below 10 psi, signaling that fuel pressure is getting dangerously low. This is essential because adequate fuel pressure is vital for the engine to function properly and for ensuring that the aircraft can safely manage its fuel supply.

When the fuel pressure falls below this level, it can lead to engine performance issues, potentially compromising safety and operational integrity. Thus, the activation of the FUEL PX light serves as a crucial alert to the crew, prompting them to take necessary actions to investigate or rectify the situation before it leads to more serious problems.