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Thunderstorms/Pilots/AFSS/ and ATC

By Michael Lenz
Reprinted with permission from FAA Aviation News

An 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.

The Aeronautical 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 areas.

  • 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 the idea.

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 your route.

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.

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