Understanding VFR Into IMC Accidents

The lethality rate of weather accidents, in other words the chances a fatality will occur in such an event, is around 63%, one of the highest among all accident types. Of these weather-related accidents, half involved attempts to continue to fly under Visual Flight Rules (VFR) into Instrument Meteorological Conditions (IMC). Among these continued VFR into IMC accidents, more than 72% were fatal versus 17% among other types of general aviation events.

A prominent study by human factor and weather accident experts Juliana Goh and Douglas Wiegmann stated VFR into IMC accidents are "a major safety hazard within general aviation," a fact clearly supported by accident statistics.

Another reason why there appears to be so much interest in these types of accidents is they're highly preventable, because as is often the case, the pilot intentionally presses on with a flight that clearly should be terminated due to deteriorating weather conditions.

And, of course, in order to have a good plan for prevention, we need to better understand the phenomenon. Thus, Embry-Riddle Aeronautical University-Worldwide (ERAU-WW) recently conducted a study to attempt to better inform pilots about VFR into IMC and offer suggestions for prevention.

Causes And Factors
Because of the extraordinary incidence and high lethality of VFR into IMC, numerous other studies have been conducted by academia, FAA, AOPA and the NTSB on the subject in an effort to better understand causes and factors related to these accidents, all of which guided the current ERAU-WW inquiry.

Of particular interest has been the relationship between flight time and accident occurrence, as well as between pilot certification and accident occurrence. Evidence supports the fact that pilots with low flight time (less than 500 hours) are involved in nearly half of all general aviation accidents. Private pilots make up around 38% of pilots, yet are involved in 49% of accidents. Commercial pilots make up 21% of the pilot population, yet are involved in 28% of accidents. Other types of pilots actually are involved in lower percentages of accidents in relation to their percentage of the population. Interestingly, student pilots make up 15% of pilots, but are involved in only 6% of accidents.

Among studies specifically focusing on weather and VFR into IMC, it has been identified that pilots often misunderstand weather or don't receive adequate education on how to interpret weather reports. According to a study by Coyne, "Despite its importance for flight safety, manypilots believe weather is the most difficult and least understood subject in their pilot training." While VFR into IMC is often assumed an unintentional digression by pilots, human factors expert Wiegmann noted that the cause of such occurrences is "often found to be a willful disregard for the regulations and cues that dictated an alternative and safer course of action."

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.

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.

However, there was also a positive correlation between flight time and VFR into IMC accidents, meaning that pilots involved in these accidents had higher flight time. Coupled with the previous finding, it appears that higher-time, lower- certification-level pilots are more at risk.

Of course, higher-time pilots are more likely to be exposed to poor weather. But it also speaks to some of those hazardous attitudes we should all avoid, specifically overconfidence in one's ability to cope with weather, that may exceed expectations and abilities. Some other relationships uncovered by the current study were that older pilots were less likely to be involved in these types of accidents.

Also, pilots flying in mountainous terrain were less likely to be on a flight plan, perhaps counterintuitive to what might be considered good practice. Other factors, such as time of day and air traffic control (ATC) communications, had weak associations with VFR into IMC, indicating such events were less likely to occur during the day and when in communication with ATC. These findings are intuitive, as poor weather is easier to see and avoid during the day, and ATC can provide assistance to pilots in trouble especially in high terrain.

Lessons Learned
So what are the "takeaways" from this study? One is that perhaps we need to examine pilot weather education. Clearly, those with lower certification levels could benefit from situational-based training (SBT) that concentrates on weather decision-making and risk assessment. With the high incidence of VFR into IMC in elevated terrain, more focus should be paid to SBT in mountainous terrain, complete with their unique weather attributes. This could easily be reproduced in simulation.

Moreover, weather-briefer training could be modified or augmented to better provide pilots with more emphasis on warnings and hazards that may positively influence pilot decision-making. Other findings, such as the fact that pilots with low certification levels and high flight times having a higher incidence of VFR into IMC, beckons improved recurrent and flight review training to include SBT and hazardous attitude evaluation specifically related to flights in or around rapidly changing or deteriorating weather conditions.

Also, the findings indicate some actions to mitigate risk in marginal weather conditions, such as avoiding night flights in such conditions, filing of flight plans and using all available resources to help keep them safe, namely interaction with ATC. Thankfully, studies such as these highlight improvements that pilots, as well as the industry as a whole, can make to improve the knowledge base and amend operational habits to make flying safer.

David Ison, Ph.D., holds a masters of aeronautical science from Embry-Riddle Aeronautical University-Worldwide. He's an assistant professor of aeronautics and program chair of the masters of aeronautical science program. A copy of his research for this study can be requested by contacting Ison at david.ison@erau.edu.