An automatic disconnect coupling, comprising: a retainer; and a biasing member coupled to the retainer and arranged to communicate excitation from a generator input member to the retainer, wherein the retainer and biasing member have a fundamental frequency tuned to rotational speed of the generator input member to automatically disconnect the input member from a drive member when rotating unbalance of the input member exceeds a predetermined level; and characterised in that, a solenoid with a core and a coil operatively connected to the retainer, wherein the retainer is fixed relative to the solenoid core, wherein the solenoid is arranged to communicate rotational imbalance of the input member as excitation to the retainer and biasing member, wherein the core is fixed relative to retainer for displacing retainer between locked position and unlocked position along retainer axis upon manual actuation, wherein the manual actuation is effected by application of an actuation current to a coil, wherein the coil extends about the core and electromagnetically couplings to the core with an electromotive force upon application of actuation current to the coil, and a manual actuation lead is connected to the coil for applying actuation current to the coil, such as by actuation by an operator switch arranged on the flight deck of an aircraft; and wherein the solenoid is dynamically coupled to the generator input member by a damping arrangement with a damping coefficient, wherein the damping coefficient is tuned such that a fundamental frequency of the retainer and biasing member is tuned to the rotational speed of the input member. a retainer; and a biasing member coupled to the retainer and arranged to communicate excitation from a generator input member to the retainer, wherein the retainer and biasing member have a fundamental frequency tuned to rotational speed of the generator input member to automatically disconnect the input member from a drive member when rotating unbalance of the input member exceeds a predetermined level; and characterised in that, a solenoid with a core and a coil operatively connected to the retainer, wherein the retainer is fixed relative to the solenoid core, wherein the solenoid is arranged to communicate rotational imbalance of the input member as excitation to the retainer and biasing member, wherein the core is fixed relative to retainer for displacing retainer between locked position and unlocked position along retainer axis upon manual actuation, wherein the manual actuation is effected by application of an actuation current to a coil, wherein the coil extends about the core and electromagnetically couplings to the core with an electromotive force upon application of actuation current to the coil, and a manual actuation lead is connected to the coil for applying actuation current to the coil, such as by actuation by an operator switch arranged on the flight deck of an aircraft; and wherein the solenoid is dynamically coupled to the generator input member by a damping arrangement with a damping coefficient, wherein the damping coefficient is tuned such that a fundamental frequency of the retainer and biasing member is tuned to the rotational speed of the input member.