An Innovative Approach for Establishing Power Train Inspection Intervals of Modern Helicopters

Modern transmissions are the product of years of development. The newest materials and software are typically used to design helicopter power trains that are expected to safely endure operations traditionally characterized as representing composite worst-case usage, a level of usage severity that is well above the limits established in the OEM flight manual. In addition, the introduction of Helicopter Flight Data Monitoring programs has systematically constrained the actual usage to a level of severity that is substantially below that allowed by the OEM flight manual. Validation projects have enabled experience to be accumulated with a variety of helicopters and this has demonstrated that many helicopters are currently operating in a way that is best described as involving benign usage. This is partially because the assemblies are so robust and partially because some helicopter usage is systematically constrained to the flight profiles that are actually needed to accomplish the missions. This paper finds that a significant portion of most modern helicopter fleets actually experience benign usage. This finding supports the conclusion that helicopter OEMs can and should provide operators with the option to choose either the traditional inspection intervals for unmonitored operations or choose a set of longer supplemental inspection intervals for helicopters involved in monitored flight operations.