Although the modern history of human factors may be traced back to Frederick W. Taylor, who carried out various studies to determine the most suitable design of shovels, human factors have only been an important element of maintainability work since World War II [1,2]. During this war the performance of military equipment clearly proved that equipment is only as good as the individuals operating and maintaining it. This means that people play an important role in the overall success of a system. Systems may fail for various reasons including poor attention given to human factors with respect to maintainability during the design phase [3].