Thunderstorms/Pilots/AFSS/ and ATC
By Michael Lenz
Reprinted with permission from FAA
airborne encounter with a thunderstorm can result in a badly shaken pilot at
best or a damaged aircraft or fatal accident at worst. Most of us know better
than to fly blindly into convective weather, and we successfully avoid such
encounters, but enough accidents bear witness to the fact that some pilots do
manage to get themselves into trouble. In the majority of those causes, the
facts show that the pilot inadvertently penetrated an area of severe convective
weather. We might ask ourselves, why a pilot would fly into a thunderstorm? Why
didn’t the pilot know there was a thunderstorm there? Why indeed?
Thunderstorm accidents are
dramatic, and they invariably depict a very interesting chain of events.
The following account from an
Aviation Safety Reporting System (ASRS) report by a Mooney M-020 pilot provides
one clue and relates to encountering some nasty towering cumulus.
“I had received permission to
deviate to the SSW from Daytona Beach Approach and the controller handed me off
to Orlando Approach. Orlando directed me to intercept V-3, when able. I was
unable to find a pathway between the towering clouds. The controller said he
needed me to take up a heading to the airway, and although I explained that I
was deviating to avoid the buildups, he said I was flying IFR and he needed me
to take up a heading to the airway. The ride was so rough I was forced to
deviate from the heading to return to calmer air. The controller said that I
could not continue to deviate without first asking for permission and that he
needed me on the airway because there were jets that needed to descend to my
altitude. The controller instructed me to climb to 8,000 feet and there was so
much turbulence that I could hold my altitude only within about 500 feet due to
rather violent up and downdrafts. This wild ride had lasted for about six
minutes when I reached the airway.”
A second clue might be found
in a second encounter with convective weather that resulted in a fatal accident.
In this case, the same transmission from air traffic control (ATC) may have had
two very different meanings to the pilot and the controller. The pilot, while
deviating around a storm, was told to proceed direct to his next flight plan
waypoint “when able.” To the controller, this meant that after deviating, you
should proceed direct. To the pilot, who has been receiving ATC help in getting
around storms from the last ATC facility, this may have meant, “You’re clear of
the weather, now you can go direct.” This accident involved three fatalities.
Another accident points out
the difficulty in making a visual assessment of severe weather. Here the pilot’s
view out the window must have differed greatly from what the approach controller
knew was there. The pilot was offered a vector for weather deviation, but
declined, saying the route ahead looked to be VFR. There was a subsequent
exchange between the pilot and controller indicating that weather deviations
would be approached and that each would be keeping the other advised. During
this time, airliners were deviating around weather in this area. The pilot flew
into a strong cell, which resulted in another fatal accident.
We can’t over emphasize how
important understanding is between ATC and pilots concerning convective weather.
For starters, tell the controller what services you want. Let the controller
know if you have no weather detection equipment on board. Be certain there is an
understanding regarding the information and services you need and your
limitations and capabilities. It may be vital to restate this, as you are
handed-off from controller to controller. The price of a misunderstanding here
can be fatal.
Some controllers are willing
to help and can provide excellent information and guidance to stay clear of
storms. Others may not be as skillful and experienced at it.
Information Manual (AIM 7-1-15) offers in part:
It should be remembered that
the controller’s primary function is to provide safe separation between
aircraft. Any additional service, such as weather avoidance assistance, can only
be provided to the extent that it does not derogate the primary function. It’s
also worth noting that the separation workload is generally greater than normal
when weather disrupts the usual flow of traffic.
To a larger degree, the
assistance that might be rendered by ATC will depend upon the weather
information available to controllers. Due to the extremely transitory nature of
severe weather situations, the controller’s weather information may be of only
limited value if based on weather observed on radar only.
The AIM goes on to point out
that deviations may be more readily accommodated in en route areas than terminal
When weather conditions
encountered are so severe that an immediate deviation is determined to be
necessary and time will not permit approval by ATC, the pilot’s emergency
authority may be exercised.
This is a safety of flight
issue. Do not hesitate to ask, even a busy controller, and remember you can
assert your emergency authority anytime safety comes into question.
Know Before You Go
A safe flight, when there is a
chance of thunderstorms begins with a good preflight briefing. This should be
done as close to departure time as practicable. Thunderstorms are explosive when
they build rapidly—growing at rates up to 6,000 feet per minute! Remember, too,
that flying on any day when then atmosphere is ripe for thunderstorms can result
in quite an uncomfortable ride, even as thunderstorms are building or when
entering areas of weak precipitation.
Automated Flight Service
Station (AFSS) briefings prioritize weather hazard areas—pointing out where you
shouldn’t go. The pilot needs to know where he or she can go. That’s a tougher
question, but here’s how to get the best information.
Once airborne, initiate calls
to Flight Watch early. One AFSS specialist I spoke with said “There’s nothing
worse than a call from a pilot who’s already in trouble. Air Traffic may not be
able to help much either.”
On convective weather days, as
soon as you’re established in cruise is probably a good time to get the first
in-flight weather update. You may think, “That’s too soon to start worrying
about it. Didn’t we just take off?” Do the math. Even a short and prompt trip to
the airplane after completing a weather briefing –with preflight, run-up and
departure routings to get established on course and at cruise altitude –can take
around an hour or longer. Time went by quickly for you because you were busy.
The towering cumulus and thunderstorms have been busy too!
In a previous weather article,
the number of pilots involved in fatal weather accidents who called for
in-flight weather was termed “dismal.” There were 19 radio contacts for weather
out of 586 accidents. Not all of these were for convective weather, but you get
To get the best information
from Flight Watch, give them what they need from you up front: Your call sign,
type aircraft (this gives them idea of your speed—a key ingredient to rapidly
building or moving thunderstorms), present position, IFR or VFR, destination and
Some AFSS’s have a new tool,
at both the Flight Watch and in flight or “Radio” positions. It’s called Oasis
and with it they can overlay your present position and proposed route of flight
on the weather radar picture. Much more importantly, they can suggest an
alternate route using airways and VOR’s that are clear of storms.
The AFSS specialist is
probably familiar with the area of storms. In fact, if you simply monitor the
Flight Watch frequency (122.0) while en route, you can learn a lot just by
listening. When it’s time to call, if you find the Flight Watch frequency
crowded, you may want to try a call to the In Flight AFSS specialist or “Radio.”
These frequencies are usually not as congested, but the specialist you talk to
may not be certified and trained to provide en route weather to the same level
as the Flight Watch specialist.
For more information on flying
safely and thunderstorms, including a convective mini-course, visit the AOPA Air
Safety Foundation’s web site at
Michael Lenz is a Program
Analyst in Flight Standards’ General Aviation and Commercial Division.