QinetiQ has completed a programme of research for the Civil Aviation Authority to investigate the causes of and factors affecting civil helicopter accidents involving operations in degraded visual conditions. A review of accident data for the period from 1975 to 2004 was carried out using the CAA's MOR database, which identified a significant number of cases that involved controlled flight into terrain, and inadvertent entry into instrument meteorological conditions (IMC) followed by loss of control due to spatial disorientation.

In a follow-on simulation investigation, two test pilots evaluated aircraft with undamped rate responses and Attitude Command - Attitude Hold cyclic control responses in flight tasks and simulated visual conditions based on typical accident scenarios. Subsequent to the trial, the pilots' ratings and objective data including pilot control demands, aircraft responses and flight path were analysed to examine the impact of visual conditions on task performance and safety for the aircraft control types flown. An examination of the sufficiency of visual scenes equivalent to Useable Cue Environments of 1, 2, 3 and poorer to support pilotage was carried out using two special techniques; image analysis and tau analysis.

The results were compared with the findings of a review of the civil regulations most pertinent to civil helicopter operations in degraded visual conditions. A conceptual framework was developed based on the findings of the studies which illustrates the strong inter-dependency between helicopter handling qualities and visual cues, and the way that these impact civil operations and requirements and, ultimately, flight safety. It was concluded that the Aeronautical Design Standard-33 Useable Cue Environment and associated response type criteria could provide the basis for safer operations in the Degraded Visual Environment, including inadvertent entry into IMC, and that the Attitude Command - Attitude Hold response type is essential for these types of operations.