New technologies of coal production have improved machine reliability but increased technical complexity. More man shifts are now devoted to maintenance than to coalface production, so maintainability is crucial. The reorganisation of craft work, to increase labour flexibility and reduce...

Although each maintenance task performed on an item of equipment may enhance its reliability, neither preventive nor overhaul maintenance can return the equipment to good‐as‐new condition. Applying the concept of maintenance improvement factors to both types of maintenance, mathematical...