only on the UH-1H and CH-47C helicopters, the nature of the maintenance systems and evaluations is such that
conclusions can be extended to all aircraft. No substantial disadvantages of the Phase Maintenance System have been
found. Advantages of the Phase Maintenance System were already demonstrated and included:
(1) More flexibility in managing maintenance operations.
(2) Significant increase in aircraft availability.
(3) Significant reduction in maintenance work hours.
(4) Significant reduction in spare parts usage.
(5) Some of the present intermediate/periodic maintenance requirements can be eliminated because they are
An optimum maintenance system provides-maximum cost effectiveness while maintaining safety of flight.
Many effectiveness indicators can be applied to a maintenance system. These indicators are ultimately related to the
comparative frequency of preventive maintenance versus unscheduled maintenance. Preventive maintenance is
preferred particularly if it is completed on a scheduled basis. Scheduled preventive maintenance allows less frequent
flight schedule disruptions, less costly repairs and minimizes secondary damage due to premature failure. Failures which
result in unscheduled maintenance reduce mission readiness, reliability and safety. The quantitative indicators of a
maintenance system's effectiveness are:
(1) Aircraft safety.
(4) Operational readiness.
(5) Maintenance work hours.
(6) Spare parts usage.
Qualitative indicators of a maintenance system's effectiveness are:
(1) Flexibility to plan scheduled inspections effectively.
(2) Adaptability to diverse operating schedules.
(3) Adaptability to diverse or variable environmental conditions.
(4) Adaptability to diverse mission demands.
Phase Maintenance Approach to Optimizing Preventive Maintenance.
Selection of components for preventive maintenance is based on the nature of the naturally occurring
degradation process for each component. Any components or systems will eventually degrade and fail to the point of