When does the fuel balancing system activate the transfer valves?

The fuel balancing system is designed to maintain an even distribution of fuel across the fuel tanks, which is crucial for ensuring proper aircraft weight and balance for safe flight operations. The correct activation threshold is determined by specified criteria based on fuel imbalance.

In this case, the transfer valves will activate when there is a fuel imbalance greater than 20 lbs for a duration of 30 seconds. This specific threshold is established to ensure timely corrective action is taken before the imbalance could affect the aircraft's performance. Activating the transfer valves in response to a 20 lbs imbalance helps mitigate risks associated with improper weight distribution and enhances overall safety.

The other scenarios provided involve either different weight thresholds or durations that do not align with the established operational parameters for the fuel balancing system. For instance, lesser weight imbalances or longer durations would either delay corrective actions unnecessarily or may not trigger the system efficiently when it is crucial to correct the imbalance.