I have been studying general aviation accidents for almost 50 years and it is amazing that over all this period of time we have lost eight, plus or minus a few, IFR airplanes to thunderstorms each year. It’s amazing because when I started there was little or no radar information on thunderstorms available, where now our cup runneth over with radar and lightning information. In 2004 there were eight airplanes lost in storms. They were high-value singles, light twins and a turboprop twin. All likely had some manner of weather-avoidance gear.
Apparently we need to step back and examine how all the available information is used, both in planning, the strategy part, and in flying, the tactics part. Tom Benenson, who is handling strategy, remarked when I told him to don his combat boots before writing that maybe we should call it “Shock and Awe.” Maybe, because it is shocking that some pilots don’t recognize thunderstorms for the awesome things that they are. But we’ll stick with “Strategy and Tactics.”
As we were discussing this, some mention was made that it might be addressed from the perspective of the new pilot and the experienced pilot. In truth, there is not much difference because thunderstorms don’t discriminate. Scott Crossfield, with more experience than the rest of us could ever hope to have, lost a battle with a storm in north Georgia recently. And a perusal of the accidents shows a broad level of experience. Of the eight 2004 thunderstorm accidents reviewed, only three involved pilots with less than 1,000 hours. The high time pilot claimed 30,000 hours.
The simple fact is that once the airplane is in a thunderstorm, experience might not count for much. So, the trick is to stay out of the beasts. Does experience help here? Are there effective ways to do this? Read on.-RLC
If you fly enough, the day will come when you will want to depart with a thunderstorm in the vicinity. The key to avoiding trouble here is found both in staying a safe distance from the rain and the mean looking clouds, and in visualizing the outflow from the storm. That outflow can make the surface wind shift almost instantly, and if it switches to a tailwind when you are at a tender point in the flight, you can be in a world of hurt. The big outflow comes on the side which the storm is moving toward and, as the name suggests, it blows away from the storm. Thus, logic suggests that you take off toward the storm, but that also means you would have to turn away from the storm after takeoff, which could involve an increasing tailwind in the turn, which might in itself create problems. Have another cup of coffee and let the storm pass.
Once we take off to fly in an area where storms exist or are forecast, the battle is joined. One definition of tactics is maneuvers designed to gain success. There are a number of things to guide us in doing this, so let’s look at all of them.
What we see is all important because before a cumulus cloud becomes a cumulonimbus cloud it goes through quite a mean building stage. With no lightning and no rain yet falling, it can dish out a level of turbulence that might make aircraft control difficult. Remember, thunderstorms don’t just exist. They also develop and the appearance of building cumulus gives the only clue here. For years I have flown with a sight level through which you can look to see if the tops of building clouds are above or below your level. It is also useful in judging how fast the clouds are building. If they are building rapidly, they might form into a thunderstorm. If there is any question about cumulus building through your level, best point the airplane in a different direction.
Congested cumulus clouds can be bad news if they build above your level and become difficult to avoid. They may or may not build into a thunderstorm but, again, aircraft control might be difficult inside those clouds.
The time of day often has an influence on the strength of thunderstorms. Like all meteorological rules of thumb this is not 100 percent true, but the middle of the morning is often when storms are at their weakest. Late afternoon is when they most like to make whoopee. Squall lines often pay no attention to the time of day, but I have seen strong ones weaken in midmorning.
Before leaving vision as a thunderstorm avoidance tool, I have to add something that has been said many times before. If clouds look mean, they probably are mean. Guidelines are given for thunderstorm avoidance: five miles for garden-variety storms, and I’ve seen numbers from 15 to 25 miles for severe storms. That may or may not be enough. The real distance, especially from severe storms, is obvious from looking at the clouds around the storm. If they look turbulent, they will be turbulent. The best deal is to visually stay away from any clouds associated with storms, especially severe storms that tend to be quite visible and quite obvious in intensity.
The up- or downlink of Nexrad information has added a most valuable tool to what you see. This has, in fact, greatly changed the tactics of thunderstorm avoidance. We can see the big picture, and by watching storms from afar we can get some idea of how they are changing in relation to a desired track or destination airport. This is important because the picture we get on the ground, before takeoff, is likely to change a lot if much time elapses before the area is reached.
While with vision, airborne weather radar and lightning detection devices, we used to fly toward an area of weather and make deviation decisions when we got close, now those decisions can be real tactical decisions that are made well in advance using the big Nexrad picture.
When dealing with thunderstorms it is best to stay clear of clouds, when you can see. Barring that, the object is to keep the airplane as dry as possible and to avoid areas where the onset of heavy rain is sudden. When using radar, an area where rain goes from light to heavy in a short distance is described as having a steep gradient. That is the signature of a thunderstorm. The picture of this is a bit better on airborne weather radar than on Nexrad because of better definition. On Nexrad, the age of the picture when received in the airplane was a big question when the equipment first came into use. I think there is general consensus that that is not a problem as long as the information is used conservatively.
A broken line of thunderstorms poses a particular en route question. Sure, there might be a gap that meets the five miles from precipitation avoidance standard for thunderstorms that are not billed as severe. But the atmospheric conditions that are spawning that broken line exist to some extent in the precipitation-free areas, so going through a gap in precipitation might yield a rough ride. The best ride would be if you could slip through clear of clouds.
Embedded thunderstorms used to be a big challenge, but Nexrad helps sort out the rainy clouds from the regular clouds. Because some rainfall rates show as heavy on Nexrad even though there is no thunderstorm, lightning detection gear or the downlink of lightning information is helpful in deciding what rain is okay to fly through and what is not okay. Certainly I have learned that, from flying with both Nexrad and airborne weather radar, and despite assurances that both offer the same picture, Nexrad paints a gloomier picture. I have flown through red on Nexrad, where I always avoid red on the ship’s radar. Flying through red on Nexrad is not something to do lightly and the decision has to be made based on gradients and lightning data.
If flying toward a low or a front with associated thunderstorms, count on them to be more numerous the closer you fly to the front. A strong squall line is actually more likely to be 100 or so miles ahead of the surface position of a front.
The controllers show weather on their scopes and have available the Nexrad picture. They can be some help with information and should certainly be consulted if there is no on-board equipment. But with the availability of portable weather receivers, as from Garmin and Control Vision, which can be carried in any airplane, every serious IFR pilot should be flying with Nexrad and lightning information.
There are conditions, especially in the Midwest, where the IFR altitudes available to a normally aspirated airplane are terribly unfriendly on stormy days. At such times, many pilots elect to fly VFR, beneath the clouds, while dodging all rain shafts.
Staying out of rain, in or out of clouds, doesn’t guarantee a smooth ride. If it’s a stormy day, the air is likely disturbed well away from rain, so always be ready to keep the airplane going through some substantial turbulence. More often than not, when an airplane is lost in turbulence the first thing that happens is a loss of control. So, control is job one.
If the turbulence is strong, the airspeed is fluctuating wildly and the rain is hard, the airplane might indeed be in a thunderstorm. If this happens, the battle is not automatically lost, but some really good flying will be required if the risk is to be managed. Forget holding altitude. Concentrate on keeping the wings level and the pitch attitude level. Adjust power to keep the airspeed as close to maneuvering speed as possible.
The conventional wisdom is to keep going straight ahead. Two reasons for that: It’s probably the quickest way out, and any intentional bank angle will put the airplane that much closer to a loss of roll control.
Having said all that I’ll qualify some of it.
If you are flying toward the east and the area of weather is moving east, the farther you fly into it, the worse it will be. An early decision to turn away here might be the best. If you are headed west into the same storm, the worst part of it will be the first part, and if you get through that then straight ahead might indeed be best.
When the destination is near, the temptation to delve into weather is the greatest.
Any temptation to fly an approach with thunderstorms in the area has to be dealt with through an understanding of the nature of those thunderstorms. What are the bases? Some thunderstorms have relatively high bases. I once took a lightning strike in smooth air beneath such a storm. Such storms are sometimes found on the slope of a warm front with the cold air beneath mitigating the flow of air down and out of the storm.
What is the surface wind doing at the airport? It can change from minute to minute but one thing is sure. If the surface wind at the airport suggests that it is under the influence of a thunderstorm, don’t go there. Major airports have wind shear detection equipment that samples wind at locations around the airport and controllers use that information to de-velop wind shear alerts.
If an approach is begun in suspected thunderstorm activity, the first sign of a strong updraft on the approach is positive word to abandon that approach. A downdraft and increasing tailwind would follow that updraft, and either can put a low and slow airplane into the ground short of the runway.
Also on approach, if there is a thunderstorm in the vicinity, visualize how the outflow will affect the landing runway. If there is no wind effect at the airport now, what will it be when the outflow of the storm gets there? I well remember landing to the southwest one day when there was a thunderstorm approaching the airport from the northwest. As I began the landing maneuver, the wind shifted to a gusty deal out of the northwest and it took every bit of available control power to manage the drift. In retrospect I should probably have gone around.
That brings us to the single most important part of the tactics of thunderstorm avoidance. Storms move, strengthen, dissipate and are temporary events. No storm ever trapped an airplane. Every airplane lost in a storm was flown into that storm by the pilot and there’s a high likelihood that the pilot knew he was trespassing on Mother Nature.
Does a high level of experience help? It can and should as long as lessons are learned from “been there and done that.” On the other hand, if a pilot suffers under the illusion that he has seen it all, trouble might be brewing because there is no “all” in relation to flying weather.
So, as with so many things, it might be said that when dealing with thunderstorms and airplanes, patience is the only virtue and impatience is the only sin.
