For the most part, pilots do a fantastic job of avoiding thunderstorms. This is probably because the dangers of flying into convective weather have been hammered into our heads since day one of private pilot ground school. Consequently, when pilots get word of thunderstorms along their route of flight, they do the safe thing: Stay on the ground, divert to an alternate if in flight, or maneuver well clear of any towering cumulus or cumulonimbus buildups.
These conservative strategies work. According to preliminary reports from the National Transportation Safety Board (NTSB), there were only 15 thunderstorm-related aircraft accidents in all of 1994. That's a very, very low number, considering the hundreds of thousands of flight hours logged by general aviation last year. Statistically, those 15 accidents are almost insignificant.
Insignificant, that is, unless you consider that all but five of those accidents involved fatalities. So while thunderstorm accidents may be few, they are more likely to kill. Most of the pilots involved in fatal thunderstorm accidents appear to have lost control in the cruise phase of flight. One of last year's fatal thunderstorm accidents took place during approach, another happened on takeoff, and another occurred while climbing. All but one of the nonfatal accidents happened while landing or taking off and seem to have been the result of encounters with wind shear or gusty surface winds.
A look at the accident reports conjures up a "typical" scenario for fatal thunderstorm accidents. It's a chain of events that sounds a lot like a "typical" VFR-into-IMC accident. The pilot takes off in good VFR weather and is aware of the potential for trouble ahead — either from a preflight briefing, a flight watch update, or a studied look out the windshield. The pilot presses on, even though the ride may become more turbulent and the view outside more ugly. Eventually, he gets in over his head and the airplane suffers a catastrophic airframe failure.
Why? If you could turn back time, stop them on their way to their waiting airplanes, and ask any of those 10 unfortunate pilots if they would ever knowingly fly into a thunderstorm, I'm sure the answer would be a resounding "No way." And yet, thunderstorm accidents occur like clockwork each year.
I believe pilots press on into adverse weather for two main reasons. One is the age-old rationale that "It'll never happen to me." While this brand of fatalistic optimism has been the eternal sustenance of men in combat (where they have little control over their fates and their lives are governed by orders from above), it should never enter the cockpit (where the pilot-in-command is in charge and it's his responsibility to come up with the rules that ensure a flight's safe outcome).
The other reason pilots press on is because conditions often deteriorate slowly, luring in the unsuspecting. It's one thing to be in good VFR conditions, see a buildup, and avoid it visually. It's quite another to be plodding along in cloud or haze, without a way to steer around storms with certainty. Flying IFR at night is the worst setup.
It doesn't take much creativity to imagine how many situations must play out. If in instrument conditions, clouds become denser and darker. Rain begins or intensifies. Turbulence, an annoyance 10 minutes ago, now requires the pilot's full attention in order to keep the airplane under a semblance of control. Preoccupied with fighting turbulence, the pilot undergoes a kind of tunnel vision in decision-making. He concerns himself with the here and now. Thoughts of an exit plan are relegated to a secondary status. A radio call or two to air traffic control may signal the urgency of the situation at this point, but by now it's a struggle to stay upright. The pilot may not even consider that he's entered a thunderstorm. The only clues may be the first glimpses of lightning ("Are those my strobe lights?") and the unmistakable sound of thunder.
If flying VFR, the flight may stumble into a thunderstorm as the pilot picks his way around a growing number of clouds. "Hah! Got past that one," the pilot thinks. Then it's time to deal with more clouds, each one darker than the last. Bank angles become steeper as the clouds keep coming. After rolling out from one heading, there's not enough distance to clear that next cloud, and then the sequence of events parallels those outlined in the previous paragraph.
Sound familiar? Count yourself lucky.
To help avoid these kinds of surprises, I mull over a kind of checklist before each flight in thunderstorm season. To be sure, a thorough preflight weather briefing tops the list, and I pay special attention to certain National Weather Service products.
The area forecast is good for a general picture of any flight precautions, gives a short and sweet synopsis, and predicts the altitudes of cloud tops. It's also essential to check the convective outlook and have a look at the severe weather outlook chart, if that's possible. The former spells out the day's anticipated convective weather; the latter portrays this information graphically. Radar summary charts (I receive them through a weather fax service) are useful tools for visualizing convective situations, but the cell locations depicted there are often hours old by the time they come churning through the fax machine. Rareps (radar reports) let you call up data from the nation's network of ground-based weather radars, give the boundaries of any precipitation echoes, and identify the locations of the highest buildups.
A check of pilot reports (pireps) is also worth a look. If there are enough, and if sufficiently descriptive, you can use pireps to confirm or reject any of the previous day's forecasts for the weather along the route of flight.
Of course, I'll also ask for any current sigmets, and review terminal forecasts along the anticipated route. If thunderstorms are forecast, and if they're associated with an advancing cold front, I'll also be sure to scope out the winds aloft. It's a well-known fact that, east of the Rockies, strong southerly flows of air — from the surface to about 10,000 feet — often precede cold fronts having the most severe thunderstorms.
Pilots should also think hard about the type of airplane they'll be flying. Single-engine, no radar, no lightning detection? Then it's safest to make sure the flight can be done under VFR. Single- or twin-engine recip, small-antenna radar, Stormscope or Strike Finder aboard? Flying IFR can be more comfortable, but understand the limitations of your storm avoidance equipment and give any returns a wide, wide berth. Multiengine, turbine-powered, and a high-powered radar? Be sure you can top or divert around any storms, and don't let the higher-performance radar lull you into complacency. Heavy precipitation can attenuate radar returns and make the worst storm cells appear relatively benign. As with any other type of aircraft, avoid any contouring radar returns by at least 20 miles and stay even farther away from any particularly sinister-looking radar signatures. These include hooks, pendants, scallops, and any returns with steep contours. Steep contours are those with little distance between each level of return. For example, if a cell shows a rapid progression from green to yellow to red, it's a safe bet that the storm is a severe one.
Geography should play a part in the preflight thought process, too. A thunderstorm in Florida is one kind of animal. A thunderstorm in Kansas is of a different species. In Florida, where highly localized air mass thunderstorms are practically a daily occurrence, visual avoidance is fairly easy. In the Midwest, thunderstorms can be more intense, cover a larger area, and make diversions more problematic.
Are there any rules of thumb to help ensure safe flying in thunderstorm season? You bet. There are no hard and fast rules when dealing with something as fluid as the weather, but here are the ones I use:
- Have a conversation with yourself. Are you comfortable with the forecast or the latest reports? If not, don't fly. It takes time and experience to become adept at flying in tricky weather situations. If you think the weather is too much for your experience level, don't fly. There's no shame in that decision, just an expression of your good judgment.
- Don't take off or land if a thunderstorm or its effects are nearby. This includes gust fronts; gusty, shifting winds; or clouds and other visibility-restricting phenomena.
- Don't fly if lines or clusters of thunderstorms are present along your proposed route of flight. If the convective outlook, rareps, or terminal forecasts indicate the possibility of thunderstorms, mentally prepare yourself — before takeoff — to reverse or alter course, or land at an alternate.
- Leave early in the morning. Thunderstorms intensify as the day wears on and surface heating builds.
- File IFR, or use flight following if VFR. Though ATC radar is not designed to portray weather radar returns accurately, air traffic control can be very helpful in alerting you to the weather ahead and providing information about alternate plans of action.
- Stay visual. The best way to avoid thunderstorms is to keep them about 20 miles off your wing tip. Don't fly beneath an anvil or other high cloud associated with a thunderstorm. Invisible hail shafts falling from these clouds can severely damage the airplane.
- Carry plenty of fuel. Diverting to an alternate airport, flying around storm cells, and having to hold because of storm-created ATC delays can eat up fuel quickly. Widespread low ceilings and visibilities may mean flying hundreds of miles to the nearest suitable airport.
- Cultivate a distrust of the smaller, less powerful airborne weather radars. While they can be a great help, they lack the power to define storms reliably. Attenuation of their signals can begin the moment rain begins, rendering them of little use at the precise time that they're needed the most.
- Keep up a conversation with flight watch. Never let yourself be caught thinking, "I wonder what it's doing along the next leg," or "Is the forecast for my destination holding up?"
- Always have an alternate plan of action for each segment of your flight. At any given stage in the flight, you should have a very good idea of what you will do should the weather deteriorate.
- Maintain situational awareness. Unless you know exactly where you are, you can't understand the relative position or extent of any reported convective activity. Nor can you know which way to turn should a landing at the nearest airport become necessary.
A thunderstorm accident can happen to you. If you previsualize worsening situations, then mentally prepare to execute alternate plans of action, you'll be better able to avoid an area of convective weather and live to fly another day.
Very often this means waiting for a few hours, or even a day, before taking off.
The pilot who just sits there — flying on but locked into inaction, hoping for the best in the face of the worst — is least likely to survive.
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