1967-02-01

Maintainability Demonstration Results and Experience 670638

Although the requirement for a quantitative maintainability demonstration has been in existence since the inception of the Air Force Specification MIL-M-26512. “Maintainability Requirements for Weapon Systems and Subsystems,” dated 18 June 1959, there are very few results of such tests reported in the literature. All major DOD contracts presently require such demonstrations in accordance with the new DOD MIL-STD-471, “Maintainability Demonstration,” dated 15 February 1966.
Since 1961, sixteen separate maintainability demonstrations have been conducted by Philco-Ford WDL under various Air Force contracts in accordance with MIL-M-26512A, B&C. All demonstrations were conducted on installed equipments in their final operating locations and environments. The purpose of each demonstration was to determine whether a given subsystem of electronic ground equipment satisfied maintainability time-to-restore requirements imposed in design and procurement specifications.
Each subsystem was different, but most of the equipment in each was electronic and was mounted in standard seven-foot racks, in a standard indoor environment. Most of these racks were designed for ready access, and their basic building blocks, the key line-replaceable unit, was usually the circuit board or logic chassis card.
For each demonstration, a sample of malfunctions was established statistically to represent the lifetime population of corrective maintenance tasks expected for the given equipment. Methods for duplicating or simulating each malfunction were determined, and the malfunctions were inserted, one at a time, into the installed equipment under as near to operational conditions as could be achieved.
After each fault was inserted, a verification was made to ensure that the expected symptoms occurred. Then, the responsible maintenance team was informed that a failure difficulty had occurred or was asked merely to check the equipment. As the maintenance team worked to diagnose and correct the malfunction, observers recorded the time, the action taken, and the equipment items involved in each apparent change in the maintenance process. Timing began the moment the maintenance team entered the area, and ended when the equipment was restored to service
This paper, in addition to presenting the results of sixteen maintainability demonstrations, describes the procedures, controls, and general conduct of maintainability testing. Problems encountered in both field and in plant testing are discussed and maintainability criteria are examined.

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