Features based on empirical mode decomposition (EMD) of measured vibration data under a laboratory controlled environment were developed for a Bell OH-58 helicopter main rotor gearbox. The data were collected at the Vehicle Technology Directorate, NASA, Glenn, Army Research Laboratory. A tooth on the input pinion of the gearbox was notched and run for an extended period at several over-torque conditions to induce a tooth fracture. Vibration data were recorded at regular intervals until a tooth fractured. The EMD features were found to be more sensitive to the gearbox condition than the kurtosis based feature (FM4) and they diagnosed the onset of cracked tooth much earlier.