Three factors play a significant role in enabling human error: operating procedures, human performance, and equipment capabilities. Through a series of case histories, the intricate nature of the relationship between these three factors is explored along with the resulting potential for human error. The need to establish expected operating procedures and functions within the bounds of intended operator capability before proceeding with equipment design is explained. It is concluded that more open technical exchange between all parties is required, if further reduction in error potential and improvements in error tolerance are to be achieved.