Abstract
This paper describes a novel power usage metric which is designed to accurately track the usage of rotorcraft power train transmissions. This power usage metric is a model for defining the relationship between input power and a Power Usage Factor (PUF) that for example increases from 0 at zero input power to 1 when the main rotor transmission is operated at 100% Normal Rated Power (NRP). The results of this process are recorded and summed over time to report the accrued mechanical usage as Power Usage Hours (PUH). This power usage product represents the hours of operations that are equivalent to operating hours conducted at 100% NRP. This power usage metric is more accurate than the traditional approach that uses flight time for scheduling the overhaul of rotorcraft transmissions. In addition the functionality is an affordable addition to HUMS installations.