A method comprising: receiving processed signals (136, 138), wherein the received processed signals (136,138) comprise signals that have been generated by applying a flight control law to a first signal and a second signal using a control law processing module, wherein the first signal has been generated by a first sensor and the second signal has been generated based on an output of a second sensor, wherein the second sensor is of a different type than the first sensor; generating an error signal (206, 379, 800, 902) based on the received processed signals (136, 138); determining at least one characteristic of the error signal (206, 379, 800, 902); wherein the at least one characteristic includes a frequency of the error signal (206, 379, 800, 902); generating one or more control signals (240, 250, 260) based at least in part on the frequency of the error signal (206, 379, 800, 902); generating a latched fault signal using a monitoring module and based on the error signal (206, 379, 800, 902), the one or more control signals (240, 250, 260) and an enable signal; and determining, using the monitoring module and based on the latched fault signal, whether to disable the control law processing module applying the flight control law, wherein a test sequencer module generates a synchronization signal based on a control signal of the one or more control signals (240, 250, 260), the latched fault signal and the enable signal, and wherein the synchronization signal is provided to a signal generation module, by a demodulation module, for use in generating the error signal (206, 379, 800, 902) and is provided to a frequency calculation module, by a detection management module, for use in determining the frequency of the error signal (206, 379, 800, 902). receiving processed signals (136, 138), wherein the received processed signals (136,138) comprise signals that have been generated by applying a flight control law to a first signal and a second signal using a control law processing module, wherein the first signal has been generated by a first sensor and the second signal has been generated based on an output of a second sensor, wherein the second sensor is of a different type than the first sensor; generating an error signal (206, 379, 800, 902) based on the received processed signals (136, 138); determining at least one characteristic of the error signal (206, 379, 800, 902); wherein the at least one characteristic includes a frequency of the error signal (206, 379, 800, 902); generating one or more control signals (240, 250, 260) based at least in part on the frequency of the error signal (206, 379, 800, 902); generating a latched fault signal using a monitoring module and based on the error signal (206, 379, 800, 902), the one or more control signals (240, 250, 260) and an enable signal; and determining, using the monitoring module and based on the latched fault signal, whether to disable the control law processing module applying the flight control law, wherein a test sequencer module generates a synchronization signal based on a control signal of the one or more control signals (240, 250, 260), the latched fault signal and the enable signal, and wherein the synchronization signal is provided to a signal generation module, by a demodulation module, for use in generating the error signal (206, 379, 800, 902) and is provided to a frequency calculation module, by a detection management module, for use in determining the frequency of the error signal (206, 379, 800, 902).