Let there be no doubt: Thunderstorms inspire fear in all pilots, high time or neophyte. And for good reason. Thunderstorms have huge amounts of destructive power and, according to the AOPA Air Safety Foundation, caused 25 percent of all fatal weather-related accidents in 2004. It's a thunderstorm's turbulence that causes most of the trouble — although convective storms also can contain deadly icing conditions, hail, and lightning. This turbulence can set off a monumental roller-coaster ride, causing dangerous swings in airspeed and/or radical upsets as the airplane rolls, pitches, and yaws out of control. Pilot disorientation usually follows, incorrect control inputs follow that, and ultimately the airplane can experience structural failure. How many times have thunderstorm accident reports mentioned witnesses saying words to the effect that airplane "parts fell out of the bottom of the clouds"? Quite a few.
Aviation safety depends on a triumvirate of attributes: knowledge, skill, and judgment. Lack any one of those attributes, and your flying isn't as safe as it should be. Assuming we all know that thunderstorms can be deadly, that leaves skill and judgment as our weapons in dealing with them.
What's the safest way of avoiding a thunderstorm encounter? Staying on the ground whenever convective activity is mentioned, of course! For any pilot — especially newly minted, non-instrument-rated pilots — that may be the best strategy. It all depends on your comfort and experience level in dealing with convective situations. But you won't develop the skills and judgment you need for wisely coping with convection by canceling flights. And you certainly won't get the most out of your airplane's utility.
Experienced instrument-rated and current pilots will find that gradual immersion is the best way to build the skills and judgment necessary for thunderstorm avoidance. The skills include developing a savvy for interpreting preflight weather information, knowing how to safely maneuver your airplane, and interpreting the in-flight weather situation. Good judgment means knowing, yes, when to stay on the ground, plus mastering the ability to formulate alternate plans of action and carry them out. The emphasis, as always, is on thunderstorm avoidance.
The preflight weather briefing is the first step toward safe flying in thunderstorm season. You'll want to be sure to obtain any convective sigmets, along with all the other usual products that briefers should issue.
Surface analysis charts can be quite helpful, although they're sometimes overlooked. It's important to remember that most thunderstorms occur in the "warm sector" of a frontal complex. This sector is east of any cold fronts and south of warm fronts. It's in this region where high temperatures and dew points conspire to set off thunderstorms as the day progresses. When checking METARs from airports in the warm sector, look for dew points of 65 degrees F or higher. This indicates a high water-vapor content. As air parcels rise, this high moisture content provides the fuel for further lifting aloft. Dew points above 70 degrees should serve as warnings, so don't be surprised if convection occurs when a region of high dew points appears.
The warm sector is also a place where southerly winds prevail. Except for the western states, these winds transport lots of moisture from the Gulf of Mexico, along with plenty of warm air from more southerly latitudes. You'll notice that those southerly winds are strongest just in advance of any oncoming cold fronts. This is one reason why lines of thunderstorms and huge mesoscale convective complexes (MCCs) can crop up ahead of cold fronts.
Telephone briefings are fine in most cases, but these days we have many additional sources of convective information via the Internet. Most of these briefing products use graphics, so interpreting them is usually stone simple. A picture is worth a thousand words, so please be sure to check out the graphics on the following links on the Aviation Weather Center's Aviation Digital Data Service (ADDS) Web site's convection tab:
Yes, there are many other excellent Internet sources for great weather depictions. But ADDS, to me, is a wonderful, free site for one-stop shopping. And it includes some of the latest products from our best centers of meteorological research.
To keep the weather flying excitement to a minimum, try using these rules of thumb:
Let's say the worst has happened: You've flown into a thunderstorm. Now what? The top priority is slowing the airplane to maneuvering speed and preparing it for a bout with turbulence. In retractables, extending the landing gear can help stabilize the airplane. Go to the power and pitch settings that you (hopefully) have previously determined will yield maneuvering airspeed. Above all, do not extend the flaps. This will reduce the size of your maneuvering flight envelope, and much more easily expose you to structural overloads.
Next comes a call to ATC to alert it of your predicament. Controllers may be able to help direct you away from the worst of the cell, but first they need to identify you on radar. This is where being on an IFR flight plan can really help speed your exit from danger.
Any turns should be made with very gentle banks. This keeps wing loadings and G-loadings down. By all means, do not try to maintain an altitude. This will only cause dangerous airspeed excursions as you chase the altimeter's and vertical velocity indicator's needle swings. Instead, ask ATC for a block altitude — say, from 5,000 feet to 10,000 feet, or as is appropriate for your level of turbulence — and fly attitude. Keep the wings as level as you can, keep the attitude indicator's "nose" on the artificial horizon, and accept any altitude deviations.
Icing conditions are common in thunderstorms, so be sure your pitot heat is turned on, and that you use any other anti-ice equipment at your disposal.
It's not a good place to be, that's for sure, and it's certainly not the sort of weather-flying experience we are all looking for. But if you follow the rules we've just discussed, you shouldn't ever have a front-row seat in a thunderstorm encounter.
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