Crashworthy Seat Cushion Change Considerations

There is currently an emphasis on improving mission capability in helicopters through improved seat occupant interface. The current issues primarily revolve around lower back fatigue as well as numbness and pain in the legs. While much of this issue is the result of cockpit design and its ergonomic interface, seat cushions are seen as a way to improve the mission capability. Cushion changes, if not done properly, can lead to degradation of the seat's crashworthy performance. Thus, changes should be carefully evaluated prior to incorporation. Typical problems that can result from a cushion change include increased seat stroke, increased pelvis acceleration and lumbar load peaks, submarining of the occupant under the lap belts and spine misalignment during vertical loading. With any cushion change the responsible parties should consider the potential impacts and test or analyze to ensure that the impact is not hazardous to the seat user. This document provides a description of some of the potential hazards associated with cushion changes and the recommended validation actions. These recommended actions are independent of requirements of the certifying or qualifying authority. In addition, the document provides a brief summary of a recent program to upgrade cushions on a Navy program.