In-Flight Emergencies: Surviving a ride in a thunderstorm

Immediate Action Items

• Try to hold a level attitude; accept altitude excursions
• Slow to VA (maneuvering speed)
• With retractable-gear airplanes, extend landing gear
• Disconnect autopilot
• Turn on anti-ice equipment
• Tighten seat belts and turn up cabin lights
• Maintain heading as best you can

Stumbling into a thunderstorm. It's the stuff of every pilot's nightmares. What makes the fear even more plausible for pilots of small general aviation airplanes are some of the inherent shortcomings bound up in this kind of flying. Because piston singles and twins don't cruise as fast as turbine-powered airplanes, there's more time for fast-moving weather to change between the time of a preflight weather briefing and the time of any en route weather encounter. If a small airplane has weather detection equipment, it has built-in shortcomings. Lightning detection equipment can give a false view of a storm's shape or location. Low-powered radars with small antennas can't effectively portray storm contours, or penetrate areas of moderate to heavy rainfall due to attenuation of radar signals. Worst of all, piston-powered airplanes fly in the lowest layers of the atmosphere, where clouds are densest and most prevalent.

When instrument meteorological conditions prevail, those of us who fly with piston engines are much more likely to fly in the soup than those with turbine equipment. And if you're on instruments, you can't see a storm cell embedded in clouds and lurking ahead. At night, visual avoidance of storms and their associated clouds-the all-time, bar-none, absolutely bulletproof way of avoiding thunderstorms-is even more difficult.

So while all pilots should fear an inadvertent thunderstorm penetration, it's probably more important for piston drivers to understand the procedures to use should a storm be encountered. This isn't to say that pilots of turboprops and turbofan-powered airplanes aren't exempt from straying into storm cells. Some of the most prominent accidents in recent history have proven that.

Here's a basic storm-penetration checklist you should keep in mind whenever your route includes a chance of thunderstorm activity. It assumes that the worst has happened: You've flown right into a thunderstorm, it's too late to think your way out, and it's time for some kind of action.

Fly attitude. This is the prime directive. Do your best to keep the nose on the attitude indicator's artificial horizon and keep the wings level. This is the best way to keep both airspeed and G-forces to a minimum while in the storm. Inform ATC of your predicament. Controllers may be able to help you with information about nearby airports or the extent of any precipitation echoes that their weather units' radars may be painting, and can provide other helpful radar services-even if it's just a voice to talk to.

Accept altitude excursions. Don't chase the altimeter in an attempt to hold an assigned altitude. Instead, fly a level pitch attitude as mentioned above. Tell ATC that you'll need a block altitude clearance so that you can ride the updrafts and downdrafts with its knowledge and consent.

Set up V_A (maneuvering speed), V_B (maximum gust intensity speed), or turbulence penetration speed-whichever is published in the airplane's pilot's operating handbook. You should know the power settings that yield these airspeeds. Go to those power settings, because airspeed fluctuations will make it impossible to use the airspeed indicator as a reference.

With retractable-gear airplanes, extend the landing gear. This will add drag and help to prevent dangerous airspeed increases. It may also aid directional stability, owing to the strake-like effect of the extended gear. You may lose a gear door in turbulence or experience momentary overspeeds past V_LO or V_LE, but this is an acceptable tradeoff for preserving a reasonable airspeed.

Do not extend the flaps. An airplane's flap-extended flight envelope is relatively small. As a result, an airplane with flaps extended can more easily suffer G-force-related damage and structural failure in turbulence.

Disconnect the autopilot or wing leveler-if your airplane has this equipment. An autopilot will try to hold heading and altitude. A wing leveler will fight to keep the wings on an even keel. Pitching up and down to hold altitude, and banking constantly to hold heading, is what you don't want when flying in a thunderstorm. This will also subject the airplane to high G forces. Yes, autopilots should automatically kick off line when they're subjected to extreme commands, but don't count on it. Turn the autopilot off before it begins sending wild pitch and bank commands.

Turn on pitot heat and any other anti-ice equipment. Thunderstorms imply icing conditions as well as severe or extreme turbulence, so use everything you've got to keep ice off the airplane.

Tighten seat belts and secure objects in the cabin. You could be bounced around to a fare-thee-well, so make sure you and your passengers have your belts cinched up tight. You should never have loose objects lying around the cabin. You'll find out why if you ever fly into a thunderstorm.

Turn up instrument and cabin lights. Should lightning strike near you, the flash can be blinding. Your vision will restore much quicker if these lights are turned up. Lightning strikes to airplanes have the potential to knock out electrical systems, but current usually passes harmlessly through the airplane.

Maintain your heading. Turning can induce huge G forces, and the quickest way out of a storm is often to just bear with it and forge ahead. A 180-degree turn could be disastrous, because of high, turbulence-induced G loads during the prolonged time required for a standard-rate-turn course reversal. If course corrections are needed, make heading changes slowly and with minimal bank angles.

Keep your wits. Of course you're scared. But remember that others have made it through thunderstorms. By following the advice listed above, you're doing all that you can to avoid the worst outcome of a clash with a thunderstorm.

Even discussing flight into a thunderstorm can be hair-raising, so maybe this is a good time to make a short review of the tried-and-true methods of storm avoidance. Here are a few of the most important items:

Fly early in the day. That's when convection is at its lowest. Stay visual. Remain at least 20 nm from any cumulus buildups. Don't try to fly through a gap between buildups. The gap could close. Don't allow yourself to be trapped on top of building cumulus clouds. In the end, you won't able to outclimb them, and you'll end up in convective clouds. Don't try to fly under a thunderstorm's cloud bases. A downburst or microburst could swat you out of the sky.

Obtain a good preflight briefing, and stay informed during the flight. This means knowing thoroughly the current and forecast weather along your route, and checking in with flight watch (122.0 MHz) while en route.

Turn back or land at the first sign of growing cells crossing your route of flight. If forecasts call for thunderstorms with the potential for covering more than 50 percent of the area along your route of flight, be spring-loaded for a 180-degree turn or a diversion to an alternate.

Follow these guidelines, and your summer flying should be as safe and surprise-free as it comes.