During a fuel system inspection, when should you check all valves located downstream of boost pumps?

Checking all valves located downstream of boost pumps when the pumps are operating is crucial because this is the only time that the system is under normal operational conditions. When the pumps are turned on, fuel is actively flowing through the system, which allows for an effective assessment of the valves' functionality. This ensures that the valves can properly open and close under pressure and that there are no leaks or blockages when fuel is being delivered to the engines.

Furthermore, performing this inspection while the pumps are operating provides valuable information about the fuel flow dynamics and potential issues that only appear under operational pressure. Issues such as valve failure due to wear or improper seating, which could lead to fuel starvation or contamination, become apparent only during this active state.

Conducting this inspection at any other time, such as when the pumps are off, does not provide the same insight because the system is static, and potential problems might not be detectable without the flow of fuel.