The Gearbox Fault Detector is an artificial neural network based defect detection system for the helicopter gearbox. This system will detect defects in the helicopter tail rotor gearbox and also classify the type of fault. Several (four) sensors will be installed on various locations of the gearbox. The data will be continuously fed into a pretrained artificial neural network system (ANS) in real time without pre-processing. The ANS will then process that raw data and indicate if a fault exists and, if so, what type of fault exists inside the gearbox. The unique significance of this system is the use of a new neural network training algorithm, called the "Delta-Activity" algorithm to train the neural network. This algorithm can accelerate the neural network learning process, overcome learning instabilities, and optimize the net configuration. It is now possible to solve much more difficult problems on a small computer, such as an IBM-PC, within a reasonable time.