Under what condition will the FUEL BAL annunciator illuminate?

The FUEL BAL annunciator illuminates when the fuel weight difference between the left and right fuel tanks exceeds 30 lbs for more than 2 minutes. This design is intended to ensure that the pilot is alerted only when a significant imbalance occurs, which could affect the aircraft’s performance and handling. By requiring a time element in conjunction with the weight difference, it helps to prevent unnecessary alerts that may occur due to transient conditions during flight, such as fuel transfer or changes in fuel consumption.

The choice emphasizing “more than 2 minutes” ensures pilots focus on genuine imbalances that could result in handling difficulties, thereby contributing to enhanced safety and operational awareness during flight.