A fault-tolerant actuating system with at least one flap, adjustable on a respective wing of an aircraft, and with a control and monitoring device, includes: drive devices that are functionally connected to the control and monitoring device, with one of these drive devices in each case being associated with a flap, where each flap in each case is associated with a drive device, in each case including: two drive motors, two brake mechanisms, where each drive motor is associated with a brake mechanism for stopping rotation of the output of the respective drive motor, a differential that couples the outputs of the aforesaid to the aforesaid in a summing manner, an output shaft for coupling the output of the differential to drive connections, and a differential lock that is functionally connected to the control and monitoring device, which differential lock is coupled to the control and monitoring device in this manner, where each of the brake mechanisms as well as the differential lock can be operated by way of a command signal from the control and monitoring device; adjustment devices, that are coupled to the respective drive device associated with the flap, where each adjustment device in each case includes: a transmission gear unit, an adjustment mechanism and a position sensor that is functionally connected to the control and monitoring device for acquiring the adjustment state of the flap; where the control and monitoring device includes: an actuating function for generating command signals for the drive motors for adjusting the flap, a monitoring function by way of which a command signal is transmitted to both brake mechanisms and to the differential lock for operating the aforesaid when the control and monitoring device based on a comparison of sensor values of the position sensors on two different adjustment devices of a flap determines different adjustment states that exceed a predetermined extent, and a method for monitoring an actuating system.