What does it indicate if the M FUEL BAL annunciator is lighted?

The indication that the M FUEL BAL annunciator is illuminated means that the fuel balance switch has been set to the MAN/RESET position. This setting is used to manually reset or adjust the fuel balance in the aircraft’s fuel system. When the switch is in this position, the system is actively balanced, and the light serves as a reminder to the pilot that manual intervention is occurring.

In a properly functioning system, the goal is to maintain balanced fuel levels to ensure optimal aircraft performance and stability. If fuel levels begin to shift, the pilot may need to engage this mode to redistribute fuel or verify the system’s functionality. Thus, the illumination of the M FUEL BAL warning is a direct result of the operational setting of the fuel balance switch, confirming that the pilot has taken control of the fuel distribution process.