Aircraft control forces and EMG activity in a C-130 Hercules during strength-critical maneuvers

Background: The force levels required to operate aircraft controls should b e readily generated by pilots, without undue fatigue or exertion. However, maximum pilot applied forces, as specified in aircraft design standards, we re empirically derived from the subjective comments of test pilots, and may not be applicable for the majority of pilots. Further, experienced RNZAF H ercules flying instructors have indicated that endurance and fatigue are pr oblems for Hercules pilots. The aim of this study was to quantify aircraft control forces during emergency maneuvers in a Hercules aircraft and compar e these forces with design standards. In addition, EMC data were recorded a s an indicator of muscle fatigue during flight. Methods: Six subjects were tested in a C-130 Hercules aircraft. The maneuvers performed were low-level dynamic flight, one engine-off straight-and-level flight, and a two-engine s-off simulated approach. The variables recorded were pilot-applied forces and EMC activity. Results: Left rudder pedal force and vastus lateralis act ivity were both significantly greater during engine-off maneuvers than duri ng low-level dynamic flight (p < 0.05). Maximum aircraft control forces for all controls were within 10% of the design standards. The mean EMC activit y across all muscles and maneuvers was 26% MVC, with a peak of 61% MVC in v astus lateralis during the two-engine-off approach. The median frequency of the vastus lateralis EMG signal decreased 13.0% and 16.0% for the one engi ne-off and two-engine-off maneuvers, respectively. Conclusion: The forces r equired to fly a Hercules aircraft during emergency maneuvers are similar t o the aircraft design standards. However, the levels of vastus lateralis mu scle activation observed during the engine-off maneuvers can be sustained f or approximately 1 min only. Thus, if two engines fail more than 1 min befo re landing, pilots may have to alternate control of the aircraft to share t he workload and enable the aircraft to land safely.