General aviation accidents in degraded visibility: a case control study of 72 accidents.

BACKGROUND Accidents in degraded visibility continue to account for a disproportionately large number of fatal crashes and fatalities in general aviation (GA). However, the relatively small percentage of these crashes annually suggests that even a small reduction in the number of crashes can result in a large reduction in associated fatalities. OBJECTIVE This study identified risk factors associated with GA accidents that occur in degraded visibility. METHODS Data collected during 72 National Transportation Safety Board investigations of GA accidents were compared with data collected from 135 control flights matched on weather conditions, location, time, and rules of flight. Study variables included pilot demographics, experience, testing and accident histories, and the purpose and length of flights. Initial comparisons were conducted using Chi-square analyses, followed by the development of a logistic regression model. RESULTS Univariate analyses identified significant differences in pilot age at accident, age at initial certification, certificate level, instrument rating, testing performance, and previous accident involvement. There were also significant differences between groups related to aircraft ownership, purpose of flight, and intended flight length. The logistic regression revealed significant increased risk for pilots initially certified after age 25 [odds ratio (OR) 4.5, 95% confidence interval (CI) 1.9-10.81, without instrument ratings (OR 4.8, 95% CI 1.8-12.8), with prior accidents/incidents (OR 3.1, 95% CI 1.1-8.7), and for intended flights longer than 300 nmi (OR 4.6, 95% CI 1.6-13.8). CONCLUSIONS Certain risk factors (e.g., instrument rating) were consistent with previous research, while others (e.g., age at certification) raise questions for future research.