Bearing Replacement Interval Extension for Helicopters

Abstract

For operators and maintainers, extension of maintenance intervals is desired to alleviate costs. For aircraft and helicopter components, traditional failure time based reliability assessment methods can seldom be applied as the reliability is often very high and defect occurrence tends to be rare. In this paper, methods to develop a conservative estimate of the reduction in reliability are explored. A case study is performed on available data from a helicopter gearbox bearing to evaluate the extension of bearing replacement interval from 2,000 to 3,000 h. The basic reliability assessment using the bearing rated life and Weibull plot equation is first carried out. The basic assessment is then improved by building confidence bounds using the Monte Carlo Simulation method. The assessment then takes into consideration data from flight usage monitoring and lastly, a probabilistic modeling of damage accumulation is attempted. From this investigation, a conservative estimate of the change in reliability from interval extension is obtained.