into IMC Accidents - General Sources
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.
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:
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."
"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"
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.
Pilots may feel pressured to reach their when they have passengers on
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
|Lack of Instrument Time
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).
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
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.
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
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.
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.
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.
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.
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.
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!
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.
advanced training. Why not get that Commercial certificate or
Instrument rating you've been thinking about.
where the terrain is. Add a GPS with terrain capability to your
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
|October - March
While returning to the S.F. Bay Area
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.
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