Apparatus is disclosed for disabling on-board pilot operation of an aircraft and transferring aircraft operation to an alternate source of control. The aircraft has an aircraft control system for controlling at least one controlled component, such as an aircraft attitude control surface or an aircraft engine throttle. The apparatus is of modular construction, and includes two control modules. A first control module has an interruptible link that passes the first control signals from the control device to the aircraft control system. This first control module has a first connecting device for (i) interrupting the link and (ii) directing said first control signals to a second control module. The second control module is adapted to be connected to (e.g. plugged into) the first control module, and has a second connecting device. This connecting device is responsive to third control signals, for connecting one of (i) the first control signals received from the first control module and (ii) second control signals received from an alternate source of control, to the aircraft control system for control of the aforementioned controlled component.