Just imagine an early U.S. Mail pilot boarding the train with his mail pouch to continue westbound to deliver the mail. This may have been one of the earliest encounters of pilot vs. thunderstorm, with the pilot being unable to complete the flight as planned.
Have the odds changed with the advent of new technologies? General aviation pilots now have lightning detectors, improved ATC radar and communications, and some even are equipped with on-board color weather radar. Armed with these tools, should pilots reconsider the advice of their first flight instructors, who preached the merits of not even flying in the same county as a thunderstorm?
My first experiences in flying around thunderstorms started shortly after I got my private license in a J-3 Cub in 1955. During the last eight years, however, I have been flying weather research missions, purposefully flying into the hearts of level 6 and supercell thunderstorms for the South Dakota School of Mines and Technology in Rapid City, S.D. To date, I have more than 1,000 thunderstorm penetrations, giving me an unusual insight for what may be in store for a general aviation pilot who winds up near thunderstorms.
I am fortunate in that I fly a highly modified North American T-28 aircraft that carries a wide variety of sensor equipment to record what is inside a thunderstorm. This aircraft has been modified and equipped to make repeated flight through thunderstorms possible, if not totally routine.
The Research Technique
Our weather research hinges on the capabilities of the T-28. N10WX does not have radar, or even a stormscope. My ability to fly through a thunderstorm with the precision required for research is a team effort between the pilot and the ground crew.
I have a ground controller watching dual doppler ground-based weather radar and, in some studies, we even use two weather radars for a better look at the target storm. The T-28 ground track is taken from the on-board IFR-certified GPS and then overlaid on the weather radar scope to the ground controller, who is aware at all times of my location in the storm.
The aircraft is designed to withstand only 60 to 65 decibels within a thunderstorm, so guidance from the ground is critical.
I normally work in Class A airspace, so I also have the opportunity to use ATC radars and controllers to help in initial storm location. We have, however, worked as low as 10,000 to 12,000 feet in investigating the intensity and behavior of storms at all levels.
With that experience in mind, I find it reasonable to conclude that I would not want to be anywhere near a thunderstorm in my Cessna 172. When flying it, I apply my first flight instructors advice to the letter. Simply put, a general aviation aircraft is not likely to survive an encounter with anything but the mildest thunderstorms without some damage – and possibly disaster.
There is a lot of fiction floating around out there as to what a thunderstorm is like, both inside and immediately outside of the storm. There are four main areas that cause pilots and their airplanes trouble when it comes to thunderstorm encounters – icing, lightning, turbulence and hail.
Thunderstorms may be a summer problem, and summer may bring heat, but icing is alive and well in thunderstorms. A cold and wet cell can create conditions that will slap two inches of ice on an airframe in two minutes flat. Engine icing can also be a problem.
The T-28 is not fuel injected and is normally aspirated and supercharged – a combination that makes carb icing a real problem. Without a system to pump alcohol directly into the carburetor to assist carb heat, the engine wouldnt stay running for long. The propeller is also de-iced with alcohol and my almost iron-clad rule is that when the alcohol is gone, Im out of there.
When I can no longer carry the wing ice, the procedure is to descend to where temperatures are above the freezing level, let it melt off, and go back up into the storm. This aircraft, with 1430 horsepower on tap, can carry two to three inches of ice and maintain altitude with only a little help from the updrafts.
Lightning is also a big problem with thunderstorms. It can become very intense, with a strike visible every five to 10 seconds.
Sometimes the lightning will hit the airplane. Last summer, while flying into a supercell, I was hit by lightning that resulted in a cockpit glow for several seconds. The only damage to the airplane was a pair of burn holes on the trailing edge of the horizontal stabilizer, but an unmodified aircraft would likely sustain much more damage. This aircraft has been hit more than 20 times.
The other hazard to lightning is disorientation during some demanding instrument flying. Just imagine an intense strobe light constantly flashing in the cockpit while you attempt to keep the airplane upright and on course.
A third area of concern in thunderstorm flying is the turbulence. It is severe, and Im talking about the FAA definition of severe: Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. This is an area where the aircraft structural limits could be exceeded and requires the most attention when inside a storm.
Finally, hail can severely damage an airplane in a matter of seconds even if youre not inside the actual storm. The T-28 is armored and can withstand up to 2-inch hail, so its not that great of a concern while on the research flights, however some unprotected research instruments do occasionally get damaged by the impact of hail.
Such is thunderstorm flying. If one of the problems is a demon waiting around the corner for an unsuspecting pilot, consider that all four may be happening more or less simultaneously. I personally have encountered this fearsome foursome about five miles from the target thunderstorm I was approaching, so you dont have to be in the thick of things to get hammered by all of the bad stuff a thunderstorm can throw at you.
This is the primary reason to give thunderstorms a wide berth. I was not convinced of it, even though Id been told, until I learned the old-fashioned way.
Into the Fray
The first hail strikes on my windshield were a surprise and I had to check the engine instruments since the hail was occurring in clear air before I even got to the storm. When I looked out at the wings and could see the hail bouncing off, I became a real believer.
I have also seen many times that thunderstorms are not totally predictable in either direction or intensity. When we work a storm, we work it for an hour or so, so I get a good feel for the direction and speed a thunderstorm can attain. The only conclusion I can reach is not to trust a thunderstorms forecast or even its ground track.
The point is that intentionally flying through a thunderstorm, into a thunderstorm or even near a thunderstorm is usually a really bad idea. Its not too difficult to avoid the isolated thunderstorms you can see, so make the effort to do so.
Imbedded thunderstorms are another matter. Avoiding them or getting out of them is certainly more difficult if you are on an instrument flight in actual IMC and have no clear visual indication of what lies ahead.
Having a spark detector or airborne radar makes the picture a little clearer, but it still is far from perfect. Thats the primary reason we use ground-based weather radar when were making research flights into the storms. Thats the only way to get the big picture needed to operate in the areas where we do research.
An airborne radar or even ATC radar, which is optimized for tracking traffic, are not adequate tools to navigate safely around or close to thunderstorms. The big surprise with thunderstorms is what might be lying around the corner undetected. During my research flights, my ground control is monitoring the situation closely and that is the only way to avoid unpleasant surprises.
With the stakes high and the danger escalating, general aviation pilots have few options if theyre flying IFR in an area bristling with thunderstorms. When I conduct safety seminars, I ask pilots what they would do if they inadvertently penetrate an area that starts to feel like a thunderstorm. Some of the answers I get are troubling. Too many times the answer is, Press on, because it cant last too long and the shortest way out may be straight ahead.
Many pilots come to this conclusion simply because they doubt their ability to make an instrument 180-degree turn and retreat out of harms way. Others take the AIMs instruction to plan and maintain course to take you through the storm in a minimum time to mean hold your original course and it will take you through the storm in a minimum time.
In almost all cases, it is safe to turn around, whereas to not do so could lead to disaster. I have been inside some storms for six to eight minutes and the specialized aircraft I was flying is the only one I know of that could come out the other side.
When the storm grabs me, the instrument flying technique I use is one of attitude flying. I must be able to ride with the turbulence so the airspeed is 140 knots indicated and the speed can be kept within -10 and +15 knots. I do this with a combination of power and altitude changes. Airspeed control is essential and is the biggest challenge in getting out of thunderstorm conditions.
The T-28 does not have a published maneuvering speed as such, because military operating manuals are developed to different standards and with different nomenclature than civilian flight manuals. The military does have a turbulent air/thunderstorm penetration speed, which I use for my operation. In civilian airplanes, use Va if thunderstorms are inadvertently encountered.
The use of power is an important tool to help control airspeed in a thunderstorm. Keep in mind, however, that you may not have the full range of power available because you may be limited in how little power you can hold. An engine can cool to critical temperatures inside the cell, and you must keep the engine warm enough to prevent carb icing, if so equipped.
In the T-28, for example, the minimum power setting is 25 inches of manifold pressure to ensure the radial engine stays warm enough to keep cranking. If you cant reduce power enough to control increasing airspeed, the only thing left to do is raise the nose and allow the airplane to climb.
In any storm, all updrafts end at some point, followed by a downdraft. In a downdraft, full power is available and the airspeed can fall lower than Va, so downdrafts are easier to work with.
If you start an immediate 180-degree turn at the first signs of thunderstorm conditions, any updraft should be short in duration. The important thing to remember is not to try to maintain your assigned altitude, as very high or low airspeeds can result very quickly. This situation is an emergency and any required actions to cope with the emergency are legal and appropriate.
I normally operate with a 3,000-foot altitude block, which is sufficient for most storms. However, sometimes I have had to tell ATC of my inability to remain within the block. I have always had excellent cooperation in working this problem.
You might not intentionally fly into a thunderstorm, but solid IFR conditions and embedded thunderstorms may result in an inadvertent entry. Keep airspeed under control, notify ATC that youre turning around and will probably make altitude deviations to cope with the updrafts and downdrafts.
A perfect standard-rate turn is ideal, but holding 20 degrees of bank on the attitude indicator will make the turnaround much easier.
Who knows, maybe I will see you someday, boarding the same westbound train when we cant complete our flights as planned because of thunderstorms. That would surely be much safer than pressing on into the unknown, and might be a lot of fun, too.
-by Charlie Summers
Charlie Summers is chief pilot for the Institute of Atmospheric Sciences at the South Dakota School of Mines and Technology. He is a Gold Seal CFI with more than 14,000 hours.