The system effects of calibration reliability on maintenance production

Maintenance for a fleet of aircraft can be viewed from a systems engineering perspective. Not only are the aircraft complex systems, the logistics of maintaining airworthy systems depend on resources such as technicians, parts, and support equipment. Support equipment which falls under the Test, Measurement, and Diagnostic Equipment (TMDE) category requires periodic calibration. The calibration process verifies the support equipment's accuracy against a traceable standard, and provides for adjustment to comply with the standard. In some instances, the support equipment may not meet the standard across the full range of measurement, so it may be labeled with a limited calibration designation, which identifies the range in which the instrument's measurements are not valid. If the support equipment cannot meet the standard, it is either discarded, or it must be overhauled to address its material deficiencies. When a fleet of aircraft transitions into an expeditionary setting they transport a limited pool of equipment to minimize the logistics footprint. However, the calibration interval persists, and they are required to submit their support equipment for calibration. Typically, the schedule is known in advance, so a sufficient quantity of support equipment should be available while an asset is away for calibration. The turnaround time including outbound and return shipping combined with the time required for induction, calibration, and simple repair can impact the overall effective availability for a given class of support equipment. In one instance, a frequently used item had a 90 day calibration interval with a three week turnaround time resulting in 77% effective availability. Low effective availability can drive an increase in overall fleet operating costs as additional assets will be required to maintain the aircraft.