Multi-axis Vibration Mitigation Properties of Seat Cushions during Military Propeller Aircraft Operational Exposures

There have been increasing complaints of annoyance, fatigue, and musculoskeletal pain during prolonged exposures to propulsion-generated vibration in military propeller aircraft. The objective of this study was to evaluate the effects of seat cushions on mitigating the higher frequency (>10 Hz) multi-axis vibration associated with Navy E-2C Hawkeye operations. An E2C crew seat was used in the laboratory during exposure to a selected operational signal. Triaxial accelerations were measured at the interface between the human and cushion (seat pan and seat back). The most pronounced effects were observed at the blade passage frequency (~73.5 Hz). The highest vibration occurred at the seat pan in the fore-and-aft (X) direction of the subject (lateral direction of the aircraft). Substantial vibration was observed at the seat back in the vertical (Z) direction. Significantly lower levels of fore-and-aft (X) vibration occurred at the seat pan with all cushions as compared to the original E-2C cushion (P<0.05). The largest reduction in the X acceleration was about 40% with a mean reduction of approximately 20% among the cushions. The results raised questions regarding psychophysical effects and whether the vibration mitigation at the blade passage frequency is sufficient for reducing the reported symptoms. INTRODUCTION Back pain in crew members has been documented in both rotary-wing and fixed-wing propeller aircraft . However, poor posture has been identified as the primary contributing factor, particularly in helicopters 6, 8, . More recently, increasing reports of annoyance, fatigue, and even symptoms of back pain have received more serious attention in propeller aircraft. These symptoms have been associated with increased aircraft vibration and exposure to longer missions associated with current international affairs. One particular case involves the U.S. Navy E-2C Hawkeye, a carrier-based early warning command and control platform. The Navy conducted a survey of 185 E-2C aviators that included 42% Pilots/Copilots and 58% Navy Flight Officers or NFOs. The results indicated that 80% of the respondents had experienced neck and/or back pain in a one-year period. The majority of these individuals indicated that the pain lasted for at least Approved for public release; distribution is unlimited. AFRL/WS-05-2250 (27 Sep 2005) 23 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 27 SEP 2005 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Multi-AXIS Vibration Mitigation Properties of Seat Cushions During Military Propeller Aircraft Operational Exposures 5a. CONTRACT NUMBER