The present invention provides test equipment for testing an additional center tank (ACT) system of an aircraft. The ACT system comprising control means configured to perform functions of an Auxiliary Fuel Management Computer (AFMC) and an Auxiliary Level Sensing Control Unit (ALSCU). The test equipment comprises at least one test module adapted for coupling to the ACT system in place of at least a portion of the control means, the test module comprising means for generating one or more test signals and outputting the test signals to the ACT system.