Drive System Loss Of Lubrication Operation

The ability of a rotorcraft to remain operative for a given amount of time after a loss of function of the primary lubrication system is becoming an important design parameter in modern rotorcraft drive system design, since other more prevalent failures modes have been addressed and mitigated by design and detection measures. There is an industry need to improve safety and drive system loss of lubrication system performance that provides some reliable extended time for operators to fly and land safely. The design challenges and testing required for meeting the requirements can be quite difficult for the designer, program, and certifying authorities. This paper overviews the civil regulations governing loss of lubrication system substantiation and approval, overviews general design issues with loss of lubrication system operations in rotorcraft identifying the typical "hot spots" in a gearbox, explores possible design solutions, and gives a brief performance history of Bell's loss of lube testing including the successful testing of a Bell 427 main rotor gearbox.