Plane & Pilot
Tuesday, February 11, 2014

Understanding VFR Into IMC Accidents

A study of situational and pilot-related factors

AOPA's findings agreed with this statement as "most often, these fatal accidents resulted from pilots deciding to continue VFR flight into instrument meteorological conditions." Goh and Wiegmann dug deeper into VFR into IMC accidents, finding that the median number of flight hours of pilots involved in such events was lower than among other accident types. There was also a higher incidence of VFR into IMC among pilots at, or below, the private pilot certification level in comparison to higher levels of certification. Two additional studies looked at some pilot demographics and environmental factors, but few statistics were offered as support.

In an effort to better understand what may influence pilots to make and continue flights in which they're threatened by poor weather, faculty at ERAU-WW utilized guidance from the aforementioned studies, as well as new research concepts to conduct a new inquiry on continued VFR into IMC accidents.

The current investigation used a type of regression analysis, which is a method to understand how strongly variables are related to, or predict, an outcome. In this case, terrain, time of day, receipt of a weather briefing, filing a flight plan, pilot age, pilot flight time, pilot certification and communication with air traffic control were examined to see how they were related to or influenced the outcome of either a VFR into IMC accident, or an accident-unrelated VFR into IMC. In order to complete this study, 40 VFR into IMC accident reports and 40 non-VFR into IMC accident reports were pulled from the NTSB database and were mined for the previously listed factors. The resultant model indicated that the identified factors were capable of correctly classifying an accident in more than 76% of cases (which was found to be statistically significant). In short, the predictors were collectively good indicators as to whether an accident was VFR into IMC.

The study found two particular factors that provided a statistically significant influence on VFR into IMC accidents: terrain and the receipt of a weather briefing. It's not surprising that high or mountainous terrain would be more deadly for a pilot that inadvertently flies into poor weather, but there's likely more to this "story." Weather conditions are often poor or rapidly changing in mountainous areas, making it more likely that pilots be exposed to such conditions in these areas.

Moreover, pilots may be accustomed to poor weather in high terrain and be more likely to "push the limits," which seemed to be the case in many accidents in the state of Alaska. In the lower 48, the
opposite was true, with many accident pilots unfamiliar with mountainous terrain and weather getting caught up in the grip of the unique weather phenomena around hills and mountains.
As is often the case, the pilot intentionally presses on with a flight that clearly should be terminated due to deteriorating weather conditions.
Oddly, the significant majority of VFR into IMC accident pilots received a weather briefing, meaning they were concerned about the weather, or at the very least, knew of poor forecasted conditions. A significant number of weather briefings included "VFR not recommended" statements that clearly went unheeded. Therefore, the problem isn't so much that pilots aren't checking the weather, but instead are misinterpreting or ignoring clues given by Mother Nature.

Other interesting findings from the ERAU study show that as pilot certification level increased, the likelihood of VFR into IMC went down. This indicates that with experience and more advanced education, pilots are more likely to avoid such occurrences.


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