Weather Decision-Making for GA Pilots
by Susan Parson
Reprinted with permission from FAA Aviation News
Aviation has come a long
way since the Wright brothers first flew at Kitty Hawk. One thing that has
unfortunately not changed, as much is the role that weather plays in fatal
airplane accidents. Even after a century of flight, weather is still the factor
most likely to result in accidents with fatalities.
the safe perspective of the pilot's lounge, it is easy to second-guess an
accident pilot's decisions. Many pilots have had the experience of hearing about
a weather-related accident and thinking themselves immune from a similar
experience, because 'I would never have tried to fly in those conditions.'
Interviews with pilots who narrowly escaped aviation weather accidents indicate
that many of the unfortunate pilots thought the same thing - that is, until they
found themselves in conditions they did not expect and could not handle.
the broad availability of weather information, why do pilots continue to be
surprised and trapped by adverse weather conditions? Ironically, the very
abundance of weather information might be part of the answer. With many weather
providers and weather products, it can be very difficult for pilots to screen
out non-essential data, focus on key facts, and then correctly evaluate the risk
resulting from a given set of circumstances.
article describes how to use the FAA Aviation Safety Program's Perceive - Process - Perform decision-making framework as a guide for your preflight
weather planning and in-flight weather decision-making. The basic steps are:
'Perceive weather hazards that could adversely affect your flight by
obtaining all the information you need for good situational awareness.
'Process this information to determine whether, and how, the hazards create
risk to the safety of your flight.
Perform by acting to mitigate the risk and evaluate the outcome of your
you plan a trip in a general aviation (GA) airplane, you might find yourself
telling passengers that you are first going to 'see' if weather conditions are
suitable. In other words, your first preflight weather task is to perceive
the flight environment by collecting information about current and forecast
conditions along the intended route. Flight Service and DUATS are the approved
sources of aviation weather information, but there are many other resources that
can help you get the maximum benefit from your weather briefing. A few
If you have a basic idea of current and forecast conditions and weather systems
before you call the Automated Flight Service Station (AFSS) or access DUATS, it
will help you better absorb information and identify areas that require closer
investigation or discussion with the briefer. Many pilots start by getting the
big picture with televised or online weather, and then go to the National
Weather Service's Aviation Weather Center <http://aviationweather.gov>
and Aviation Digital Data Service (ADDS) <http://adds.aviationweather.noaa.gov>
for aviation-specific information. ADDS also offers interactive tools that can
help you better visualize weather conditions.
standard flight plan form, develop an estimate for altitude, route, and
estimated time en route so you can get the most appropriate information from the
AFSS briefer or DUATS.
Be honest - with yourself
and with the briefer - about any limitations in pilot skill or aircraft
capability. If you are new to the area or unfamiliar with the typical weather
patterns, including seasonal characteristics, speak up.
questions - what
you don't know can hurt you. The worse the weather, the more data you need, and
you should definitely seek a 'live' briefing from an FSS specialist before you
head for the airplane. If you are flying in instrument meteorological conditions
(IMC) or marginal visual flight rules (MVFR) that could deteriorate, be sure to
get information on which direction (north, south, east, west) to turn for better
weather, and how far (or how long) you would have to fly to reach it. Also,
don't forget to check the pilot reports (PIREPs) - fresh information from
someone who has actually experienced the weather conditions can add
substantially to your weather picture.
in your tanks is useless unless it is processed through the engine. Similarly,
weather information in your hands is worth little, unless it is processed
through your brain. Weather is certainly complex, but the good news is that you
don't have to have a degree in meteorology to effectively and accurately analyze
the weather information that you just obtained. Here's a simple way to start
processing your weather briefing data.
might remember from ground school, the three basic elements of weather are:
temperature (warm or cold); wind (a vector with speed and
direction); and moisture (or humidity). These three weather elements
combine in various ways to create conditions that affect pilots.
the range of possible combinations is nearly infinite, weather really affects
pilots in just three ways. Specifically, the basic weather elements can.
Consequently, you need to analyze your weather briefing data in terms of how
current and forecast conditions will create any of these hazards for your
flight. Use any method that works for you, but you might find it helpful to jot
information from METARs and TAFs into a format like the tables on the next page.
The columns match the order in which the weather data is presented, with labels
along the top for the three major weather impacts. Make rows to record
conditions for departure, en route, and arrival phases of flight. This method
can help you make 'apples to apples' comparisons, and to see at a glance
whether, and how, the three weather impact conditions will be present for each
phase of your flight. You might make a similar analysis of winds aloft.
you identify the weather issues for your flight, the final part of processing
your information is to evaluate whether the pilot-aircraft team is up to the
challenge. For example, you may be a very experienced, proficient, and current
pilot, but your weather flying ability will be limited if you are flying a
1980s-model aircraft with no weather avoidance gear. On the other hand, you may
have a new technically advanced aircraft with moving map GPS, weather data link,
and autopilot - but if you do not have much weather flying experience, never
count on the airplane's capability to compensate for your own lack of
experience. It also helps to compare conditions to your personal minimums.
third step, making a preflight weather plan, is a strategic, 'big picture'
exercise that should include:
there good weather within your aircraft's range and endurance capability? What
direction do you turn, and how long will it take to get there? In bad weather,
can you identify an acceptable alternative airport for each 25-30 nm segment of
where to find VFR weather will help only if you have enough fuel to reach it.
More fuel means access to more alternatives. It also spares you the worry (and
distraction) of fearing fuel exhaustion when weather has already increased your
Always know how low you can go without hitting terrain and/or obstacles. Make a
specific terrain avoidance plan for any flight that involves MVFR conditions, a
temperature/dew point spread of 4' C. or less, any expected precipitation, or
operating at night.
such as the pilot's reluctance to appear 'cowardly' or to disappoint passengers
can be very powerful, so your weather planning should include preflighting your
personal weather minimums with your passengers, and state up front that you will
delay or divert if conditions exceed these values.
know what you will do if you have to divert at any particular point. Preflight
is the time to think through alternative arrangements (e.g., hotel, rental car)
in the event that weather conditions worsen.
meeting you at your destination that you will call when you arrive, and that you
will delay or divert if weather becomes a problem.
waiting it out is one of the most effective safety tools. A single day can often
make the difference between risky and routine.
En Route Weather
weather is not severe enough to cancel the trip, many pilots choose to take off
and take a look. If you make such a decision, safety requires staying alert to
weather changes. At typical GA aircraft speeds, a 200-mile trip can leave a two
to three hour weather information gap between the preflight briefing and the
actual flight - and weather can change a lot. Use these sources of information
before you take-off:
your eyes to see whether the conditions around you match the conditions that
were reported or forecast. If not, you need to start getting more information.
Listen to ATIS and ASOS/AWOS broadcasts as you fly. If conditions are worse than
forecast, it's time to seek more information.
Flight Advisory Service (EFAS, or Flight Watch).
Available on 122.0 MHz in the continental United States from 5,000 feet AGL to
17,500 feet MSL (124.67 MHz at higher altitudes), call Flight Watch for en route
weather advisories pertinent to the type of flight, route of flight, and
Traffic Control (ATC).
If you are not already on an IFR flight plan, monitoring ATC frequencies
(available on aeronautical charts) along the way can tell you a lot. For
instance, are other GA aircraft along your route deviating for weather? Having
the ATC frequency tuned also makes it easier to request information and
and Weather Avoidance Equipment.
Data link is an increasingly popular method of getting in-flight weather
information. Data link uses satellites to transmit METARs, TAFs, NEXRAD, and
other information to the cockpit for display on the multifunction display (MFD)
or a handheld unit.
order to properly evaluate and interpret en route weather information, you need
to be aware of limitations such as:
Research has determined that weather transitions are sometimes too subtle for
the visual system. The human eye responds best to changes, including motion and
light (e.g., flashing strobe). In deteriorating weather conditions, reductions
in visibility and contrast can occur so gradually that the pilot does not notice
until there is a significant reduction in visibility.
In flight weather information obtained from ATIS and ASOS/AWOS broadcasts can
contribute useful pieces to the en route weather picture, but remember that it
is only a 'snapshot' of a limited area in the airport vicinity.
Interpreting EFAS information while you are also flying the aircraft - especially in adverse conditions with no autopilot - can be very challenging.
Keep a chart at hand so that you can quickly visualize location of weather
relative to your position and route, and determine whether (and where) you need
Traffic Control (ATC)
Be aware that radar 'sees' only those entities that reflect energy.
Precipitation density is indicated by the strength of the return and, while
radar does not detect turbulence, an intense precipitation return may imply its
existence. Similarly, icing does not show directly, but may be inferred by the
presence of moisture, clouds, and precipitation at temperatures at or below
and Weather Avoidance Equipment
Today's cockpit weather displays give pilots an unprecedented quantity of
weather data, but data link is not a silver bullet. The quality of the
information depends heavily upon update rate, resolution, and coverage area.
Accurate analysis of data link information depends on your understanding each of
preflight weather plan is a strategic tool. Use en route weather data and
analysis to make tactical ('right now') weather decisions based on what you
actually find in the air. Suggestions:
immediately if you see or suspect deteriorating weather. For example, head for
the nearest airport if you see developments such as:
forming beneath your altitude,
Gray or black
Hard rain or
forming above that require you to descend; or
below your pre-established personal minimums.
always easier to reevaluate conditions and make a new plan from the safety of an
delay. If you
need help from ATC in avoiding or escaping weather, ask sooner rather than
later. Remember that navigational guidance information issued to a VFR flight is
advisory in nature. Suggested headings do not authorize you to violate
regulations, and they are not guaranteed to keep you clear of all weather.
make assumptions about what the controller knows about your flight.
If you are
handed off while on a suggested heading for weather avoidance, confirm that the
next controller knows you are requesting this assistance.
to ATC, 'cleared direct when able' means to fly direct when you are able to
navigate directly to the fix. It does not mean that you are now clear of
weather. Always ask whether a direct course will keep you clear of radar returns
indicative of thunderstorm activity.
- Help other
your workload permits, contribute to the system by making PIREPs yourself. If
you aren't certain about how to give PIREPs, take a look at the AOPA Air Safety
Foundation's free online 'Skyspotter' course (http://www.aopa.org/asf/online_courses/skyspotter),
which includes a handy PIREP form that you can put on your kneeboard. If you
don't have a form handy, don't let that stop you from contributing - tell the
FSS specialist or controller what you see so that other pilots can benefit from
you land after a challenging flight in the weather, you probably want nothing
more than to go home and unwind. The immediate post flight period, however, is
one of the best opportunities to increase your weather knowledge and
understanding. Make it a point to learn something about weather from every
flight. Take a few minutes to review and reflect by considering these questions:
Weather is a fact of life for pilots. Developing your weather knowledge and
expertise is well worth the time and effort you put into it, because weather
wisdom will help keep you, and your passengers, safe in the skies.
Note: For more information, please go to:
Susan Parson is a Special Assistant in Flight Standards' General Aviation and
Commercial Division and is an active GA plot and a NAFI Master CFI.