HUMS Condition Based Maintenance Credit Validation

There is an increasing desire to use rotorcraft Health and Usage Monitoring Systems (HUMS) to facilitate Condition Based Maintenance (CBM) approaches to achieve operating cost reductions and other benefits. This type of application must be supported by the certification process, as it is an example of a “maintenance credit”. Guidance material on the process of obtaining a credit is presented in Advisory Circular AC 29-2C MG-15. Current HUMS have achieved very few credits, and the material in the AC is largely untested. However HUMS in-service experience shows that the potential for future credits does exist. This paper presents work performed by Smiths Aerospace and Sikorsky Aircraft Corporation (SAC) on an FAA research program, with the primary goal being to research the end-toend process for approving an example HUMS CBM credit in accordance with the requirements of the AC. The primary target CBM credit selected for the work is to extend or eliminate a current 2,500 hour TBO on the oil cooler of the S-92 helicopter. A key element of the work is to demonstrate and validate the ability of HUMS algorithms and methodologies to detect incipient mechanical faults and facilitate timely maintenance intervention. The work will assess the CBM credit potential of both the current mechanical diagnostic algorithms and methodologies in in-service HUM systems, and the additional capabilities gained through the application of emerging advanced HUMS analysis methodologies. The results of the FAA program will go into the public domain, and should be of value in helping to test and refine the guidance material in AC 29-2C MG-15, and to realise the maintenance credit potential of HUMS.