Accident Survey of Fly-by-Wire Powered-Lift Aircraft toward Understanding Variable Configuration eVTOL Aircraft Certification Risks
Abstract
This paper outlines observations from an FAA-sponsored research project that examined aviation fly-by-wire (FBW) accidents in helicopters, transport-category airplanes, and powered-lift aircraft. The goal was to identify risk areas that will help guide a focus for FAA certification testing. Part of this study specifically focused on current powered-lift tiltrotors, identifying six general categories of causal factors for accidents, which will be discussed in detail regarding how they influenced flight control designs. The results of this survey, along with extrapolation to current designs, will be discussed and will illustrate why manufacturers are moving toward state-based flight control designs. In a state-based flight control scheme, the pilot does not have direct control over aircraft attitudes and motor tilt angles. Instead, the pilot requests a speed and or flight path with inceptor input, and the commanded attitudes and motor tilts are scheduled by the flight control computer. Additionally, recent lessons learned from electric vertical takeoff and landing aircraft accidents will be discussed, along with a comparison of powered-lift causal factors to accidents in the helicopters and transport category FBW fixed-wing aircraft. From this analysis, broad observations will be offered about the trend of how accident-causal factors may evolve with greater maturity in aircraft design. This accident survey will be detailed further as part of an upcoming FAA research report titled “An Approach to FBW HQ Testing Linking Development Tools to Civil Cert Requirements.”