A winch monitoring system has a fixed-ratio gearbox with input and output shafts. A winch drum is connected to the output shaft, and an auxiliary brake is connected to the output shaft activated by reducing the pressure in a brake release hydraulic circuit. The monitoring section receives the speed signals, and processes them to produce a calculated ratio of actual input to output shaft speeds, and produces a fault indication signal when the value of the difference between the calculated speed ratio and the fixed ratio exceeds a predetermined value. The brake control section, upon receiving the fault signal, reduces the hydraulic pressure in the brake circuit using a nonlinear pressure-time profile to engage the auxiliary brake and stop the winch drum.