Whole body vibration exposure for MH-60S pilots

Pilots of the MH-60S helicopter are exposed to continuous whole body vibration (WBV). Pilot fatigue is a growing operational concern due to the increased frequency of extended durations of missions (6-8+hours) in support of Operations Iraqi Freedom and Enduring Freedom. Endurance aspects of the currently used rotary wing seating systems were not optimized for the longer missions and wide range of pilot anthropometric measurements, which is now typical of naval aviation. The current seating systems were designed primarily to meet crashworfhiness requirements, not for the wide range of pilot anthropometry or to mitigate WBV. Albeit, an issue, pilot fatigue and reduced mission effectiveness are also critical concerns. Current Hazard Reports (HAZREP) indicated that pain in both pilots' legs and backs begin 2 to 4 hours into the flight and increase with time. Situarional awareness also decreases with an increase in flight duration due to the constant distraction of pilots shifting in their seats while trying to get comfortable. Froom (1987) reported a dose-response relationship between the length of military helicopter flights and back discomfort. He also concluded that this pain is typically dull, over the lower back, and its prevalence and intensity are dependent on the total flight hours of exposure. This study evaluated WBV produced in the pilot seating systems onboard the MH-60S. The purpose of the study was to test and compare the effectiveness of three different seat cushions, the current seat cushion versus two anti-vibration seat cushions A and B. The three seat cushions were measured for acceleration levels averaged over five-minute intervals using a triaxial seat pad accelerometer. The recordings were completed for several round-trip straight and level flights. A frequency analysis from 0-80 hertz (Hz) was conducted on all acceleration measurements to determine the dominant axis and frequency of the pilots' vibration exposure. The results were then compared to the applicable Threshold Limit Values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH) [1] to determine the MH-60S pilots' permissible exposure time for all seat cushions. The results of the study showed that for all three seat cushions the vibration levels of the z-axis at 16 Hz had the shortest allowable exposure duration, according to the ACGIH TLVs, In the z-axis at 16 Hz, the MH-60S's current seat cushion almost pierced the 4-hour exposure time limit curve and anti-vibration seat cushion B pierced the 8-hour exposure time limit curve. The anti-vibration seat cushion A reached the 16-hour exposure time limit. Anti-vibration seat cushion A outperformed the current seat cushion and anti-vibration seat cushion B by exhibiting significantly reduced vibration levels. Using the criteria set forth in Military Standard 882 and DoDI 5000,2, the current seat cushion and anti-vibration seat cushion B may result in a mishap severity category III or IV. This mishap category would be consistent with IIIC, which requires Program Executive Officer approval, or IVB/C, which requires Program Manager approval for associated human and programmatic risks. These guidelines should be incorporated into the design and acquisition process and should be integrated within Capability Development Documents (CDDs) and Capability Production Documents (CPDs) that provide the basis for future requirements, funding and follow-on contract documents.