Mechanical failure occurs when a component no longer meets performance specifications. Mechanical failure modes can include deformation, yielding, crack initiation, excessive spalling, corrosion, etc. Operational failure is when the system no longer functions as intended. Operational failure follows after mechanical failure. When monitoring wind turbines and transmissions mechanical failure does not necessarily mean operational failure. A transmission may continue to function even though individual components have failed. Operational failure of a mechanical system is however, indicative of mechanical failure.