What happened
A large-scale safety study conducted by the Canadian Aviation Safety Board (later the TSB) analyzed 333 weather-related accidents involving Canadian-registered aircraft between 1976 and 1985. The investigation focused on a specific and deadly phenomenon: pilots initiating or continuing flight under Visual Flight Rules (VFR) despite encountering Instrument Meteorological Conditions (IMC).
During this ten-year period, while VFR-into-IMC accidents represented only 6% of all recorded accidents, they were responsible for a staggering 23% of all fatal accidents and 26% of all aviation fatalities. The study noted that while the total number of aviation accidents was declining, the proportion of fatalities caused by flying into adverse weather was actually increasing.
The investigation
The study utilized a systematic approach, clustering accidents with similar characteristics to identify patterns and applying the "man/machine/environment" model of safety analysis. The researchers examined various sectors, including pilot licensing, aircraft equipment, and regulatory frameworks.
Key areas of investigation included:
- The adequacy of VFR visibility minima in uncontrolled airspace.
- The risks associated with flying in mountainous or hilly terrain.
- The safety implications of Special VFR (SVFR) regulations.
- The effectiveness of pilot training, licensing, and weather briefing services.
Data showed that charter operations were disproportionately represented in these accidents, accounting for nearly 27% of VFR-into-IMC occurrences despite making up less than 19% of all accidents. Furthermore, many accidents occurred in remote regions or mountainous areas where visual references are difficult to maintain.
Findings
The investigation established several critical contributing factors to these fatal accidents:
- Inadequate visibility minima: The one-mile visibility minimum in uncontrolled airspace makes it extremely difficult for pilots to maintain aircraft control via outside reference, often leading to loss of control.
- Terrain hazards: Over half of the studied accidents occurred in mountainous or hilly terrain, where unpredictable winds and turbulence increase risk.
- Regulatory gaps: Current regulations for commercial VFR operations in uncontrolled airspace do not provide enough of a safety margin compared to international standards.
- Operational risks: The reduction of SVFR weather minima and the lack of accessible weather briefing services in remote areas contributed to poor decision-making.
Safety action
The report issued several recommendations to the Department of Transport to mitigate these risks, including increasing VFR visibility minima for commercial operations and in mountainous regions, reconsidering the reduction of SVFR minima, and improving the publicity of transcribed weather services in remote locations.