Modeling the Impact of Helicopter Vibrations on the Musculoskeletal Health of US Army Blackhawk Helicopter Pilots

Abstract

The UH-60, used for troop transport, MEDVAC, and mission control, has evolved over the last 45 years from the Alpha Model to the Lima and Mike models that are currently utilized. Previous studies investigated the impact of Whole-Body Vibrations (WBV) on aviators and the resulting musculoskeletal injury, but none have investigated the efficacy of the Mike model’s Active Vibration Control System (AVCS) on reducing the impact of helicopter vibrations on musculoskeletal health. Computational analyses of a biomechanical model using OpenSim and motion capture at varying levels of vibration was conducted. This quantifies the response of the spine and the surrounding muscles when vibratory loads are applied while positioned to manipulate the flight controls. A musculoskeletal model was developed to represent the aviator in the seated posture required to effectively manipulate the flight controls. To develop the model, the team recorded motion capture data with a pilot in a pilot test for concept validation. This data was then processed and input in the OpenSim inverse kinematics tool to determine joint angle and to demonstrate the muscle-tendon length of several muscles in the back. Unlike the initial predictions, the muscles in the right side of the back were not consistently longer than those of the left side. A survey was also developed that builds upon previous efforts, seeking to understand the aviator’s perspective on musculoskeletal injury and prevention, with a focus on the back. Aviators are asked to describe the cause of their injury, methods of injury prevention, and recovery techniques encompassing numerous subpopulations of flight experience: Lima-majority, Mike-only, Mike-majority, and an even mixture of L/M. The data attempts to characterize the impact of the AVCS on aviator spine health. The AVCS should decrease the rate of injury by reducing the vibratory loads experienced by the aviator. This survey is unique to previous questionnaires as it focuses on the user’s perspective of differences between the two models, and the injury or pain felt by each service member. While it was expected to see a trend of reduced injury occurrence amongst the Mike-only aviators versus those with Lima-majority flight hours, this was not the case. Injury prevalence was consistent across most populations, indicating the potential inefficacy of the AVCS. Analysis of open-ended responses, particularly from the hybrid group, provide some context for the perceived impacts of using the AVCS. Some population demographics were not represented in this survey due to the nature of the unit being surveyed, which may impact the validity of some results. By quantifying the perceived efficacy of the AVCS as it relates to chronic musculoskeletal injury using a survey of pilot experience factors (flight hours, airframes, operating theatres, etc.), and by representing the maladaptive posture of the pilots with a computational simulation based on experimental pilot data; a full picture is developed of the risk of issue related to the near and long-term health of US Army Aviators. The aim is to expand the overall understanding of how vibration is impacting the musculoskeletal health of aviators and their perceived impact on lifelong health from the profession. The ultimate goal is to aid in the design of additional countermeasures to improve aviator spine health and to serve as a platform for optimization of systems like AVCS.