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VFR into IMC Accidents - General Sources
VFR-into-IMC accidents are a big problem in the S.F. Bay Area.  While they accounts for about 5% of all fatal accidents in the U.S., its responsible for fully one third of all fatal accidents in the San Francisco Bay area.  There are few good articles on the topic, but here some references and tips that you can follow.  

A University of Illinois research paper analyzes 409 of these accidents from 1990 to 1997 and tests possible hypotheses on why these accidents occur.  

Here are some of the hypotheses:
Situation Assessment
Pilots press on into deteriorating weather because they don't realize they're doing so.  In other words, pilots continue from VFR into IMC "when they misdiagnose the changes in, or severity of, the weather.  The loss of situational awareness that precipitates a 'VFR into IMC' event may be due to a variety of reasons including a lack of experience interpreting real-time weather by low-time or 'fair weather' pilots."   

Risk Perception 
"Another explanation for why pilots would continue VFR flight into IMC is that  pilots are overconfident in their abilities and do not fully appreciate the risks of flying into adverse weather. Indeed, much of pilot training involves teaching pilots to feel confident in their ability to control the aircraft in all flight regimes.  However, an unfortunate by-product of this training may be a degree of overconfidence in one's skill level and an unrealistic optimism about the chances of avoiding harm through personal control....[one study showed] that general aviation pilots exhibited both relatively low levels of risk awareness and generally high optimistic self-appraisals of abilities and judgment"

Decision Framing
This is the hypothesis discussed in our July 2005 newsletter article. It suggests that pilots frame their decisions in terms of potential loses (e.g. cost of diverting to another airport) and therefore push on into bad weather, particularly if their close to reaching their destination.  This may explain the large number of VFR into IMC accidents that occur in the Livermore Valley--just short of pilot's destinations in the S.F. Bay area.

Social Pressure
Pilots may feel pressured to reach their when they have passengers on board. 

The study found what we've been telling you all along.  While about 20% of all GA accidents are fatal, 80% of VFR into IMC accidents are fatal (and the most recent numbers from the Air Safety Foundation are closer to 90%!).  What is new, is that they compared the top 11 accident factors/causes for VFR into IMC accidents with GA accidents in general.  I've added a third column to their data which shows the ratio between the two columns.

Factors/Causes VFR GA VFR/GA ratio
Weather conditions 69.2% 22.5% 3.1
Terrain conditions 24.9% 19.8% 1.3
Spatial Disorientation 23.7% .98% 24.2
Aircraft Control 23.2% 6.4% 3.6
Light Conditions 23.0% 4.89% 4.7
Lack of Instrument Time 15.9% .5% 31.8
In-Flight Planning/Decision 12.7% 5.9% 2.2
Preflight Planning/Decision 11.2% 4.9% 2.3
Weather Evaluation 11.2% 1.2% 9.3
Altitude/Clearance 8.1% 1.5% 5.4
Over Confidence 7.5% <1% >7.5

Pilot Flight Experience
The median number of hours of flying experience for pilots with VFR into IMC accidents was 580 hours vs. 900 hours for all GA accidents (statistically significant to the 99% level).

Pilot Certificates
A larger proportion of pilots in the VFR into IMC accidents had only private or student licenses (71.6% of the total), versus 57.9% of pilots involved in GA accidents.  Note: higher certificate in this case means Commercial or ATP.  The study doesn't address whether pilots had an instrument rating. 

Presence of Passengers
A statistically significantly higher proportion of VFR into IMC accidents had passengers. 54.3% if VFR into IMC accidents had passengers versus 44.7% of all other GA accidents. 

The data supports the Situation Assessment theory that pilots with fewer flight hours and less instrument time may have less experience interpreting deteriorating weather and flight visibility.   Having Nonetheless, those of us with thousands of hours are hardly immune to this accident type; one of the Livermore Valley accidents was by a 10,000 hour ATP rated pilot.   Don't fall into the trap of believing a VFR into IMC accident won't happen to you just because you're a high time pilot!  In analyzing S.F. Bay area VFR into IMC accidents, we found there was not a large advantage to having an instrument rating.

Also, the data suggests that having poor weather evaluation skills contributes to these types of accidents.  That's one of the reasons I often take students flying when visibility is less than 5 miles.  I want them to be able to see what that looks like, so that they'll recognize it in the future. 

The data also supports the Risk Perception theory that pilots are overconfident in their abilities, as this factor is more than 7.5 times more likely for these types of accidents.   While it great that pilots in general are confident, it's a little disturbing that every time pilots are surveyed, the vast majority rate their piloting skills as "above average."  Of course, that's just not possible.

The data also supports the Social Pressure theory, since a higher percentage of VFR into IMC accidents carry passengers. The researchers felt that the Decision Framing theory should not be discarded, even though they were unable to find accident data that would validate it. 

What to do about it
So instead of just talking about it, what do you do about it to avoid VFR into IMC accidents?  Here are some thoughts.

  • Check the weather.   You should be calling FSS before every flight anyway, just to make sure there are no TFR's or NOTAMs that can bite you.  You might as well check the weather at the same time.

  • Have alternate plans in mind.   Think about where you're likely to encounter weather and have a plan for what to do about it when you encounter it.  It shouldn't be a surprise to you that if you're flying back into a coastal region at night that you might encounter the marine layer.  As my kids would say, Duh!

  • If you encounter diminished visibilities, follow your plan!   That may be to do a 180 degree turn, divert to another airport, climb, request a pop-up IFR clearance or something else.  Whatever it is, don't wait to do it!  Too many accidents occur because pilots don't take action when they first detect a developing problem.  

  • Get advanced training.  Why not get that Commercial certificate or Instrument rating you've been thinking about.

  • Know where the terrain is.  Add a GPS with terrain capability to your Christmas list. 

Finally, remember that we're entering the dark time of year when you're far more likely to have a VFR into IMC accident at night.  Here are the statistics for S.F. Bay area VFR into IMC accidents during the last 10 years.

  Total VFR into IMC Day VFR into IMC Night IFR into IMC
April - September 10 8 2
October - March 14 5 9

Descent While returning to the S.F. Bay Area 
General Aviation pilots do most of their flying in the daytime.  When I surveyed pilots at safety seminars, only a small percentage of pilots indicated that more than 5% of their total flying was at night.   It's very hard to see terrain at night, so it's important that you use IFR-like procedures, and maintain a safe altitude over all terrain.  If in doubt, stay at least 500 feet above the MEF figure (the large number in each quadrangle of your VFR Sectional Charts) to assure terrain clearance.   Also, if there are common routes that you fly at night, fly them in the daytime to determine a personal minimum safe altitude for flying the route at night.  For many S.F. Bay area pilots, this might be over some of the local passes such as the Hayward and Sunol passes in the East bay, and the Altamont pass just west of the Tracy & Stockton area.  As the picture to the left shows, Sunol Pass can often be blocked by clouds.

Try to plan your flight to arrive back in the Bay area before darkness, particularly in the winter months when days are short. If you're unable to get through any of the passes, make a 180 degree turn early, and land at Livermore, Stockton or other airports where it is still clear.  Rent a car, call a friend to get you, or stay overnight in a motel.  Alternatively, you may be able to get above the marine layer, cross the bay area, and then descend in open areas near your destinations, if the local ATIS or FSS suggest that there are still cloud openings near your destination airport.  In any case, choose an alternative that guarantees that you won't end up on a mountain ridge where you'll become another statistic!

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Attention Bay Area pilots:  Max Trescott recently completed an analysis of fatal accidents in the Bay Area for the past ten years. The key results are that fatal accidents are twice as likely to occur at night as compared to the rest of the U.S. Also, VFR into IMC accidents are up to 6 times more likely than in the rest of the U.S. Register at faasafety.gov  to receive email notification of the next seminar detailing Bay area accident analysis.