Plane & Pilot
Tuesday, June 8, 2010

Dealing With Convective Weather


Some pilots simply lock their airplanes in the hangar when convective weather is about. Others learn to cope.



Shortly after returning from a recent Grand Caravan delivery from Long Beach, Calif., to Seoul, Korea, I spoke at a LoPresti First Saturday event in Sebastian, Fla. There were about 400 people present, many of them curious about the method and madness of ferry flying. Inevitably, one of the first questions I was asked was how I deal with “hard IFR” and thunderstorms. That’s obviously a major concern in Florida, especially in April through October, when tropical thunderstorms and rain are most prevalent.

Not All Bad News
The good news is that convective weather isn’t as much of a problem on the Pacific, and it’s also rare over the Atlantic. One major factor in regions of thunderstorms, thermal activity, usually is absent over the ocean. Another, orographic lift, isn’t possible when there’s no terrain to provide the launching platform for the upsloping air. The bad news is that we repeatedly cross the dreaded Intertropical Convergence Zone (ITCZ) that runs 10 degrees north and south of the equator, and we fly over land, too, especially dangerous in places such as Africa and South America.

Whatever form convection takes, however, pilots have no choice but to either deal with it or stay on the ground. It can be a special problem for ferry pilots. After all, if you’re halfway out on the 2,160 nm leg to Hawaii and you run into bad weather, you have only two choices: continue to your destination or return to the mainland. Since an abort can be an expensive option, we usually try to continue. (More on that later.)

That doesn’t mean we drive on blindly into convective weather. As the crash of an Air France Airbus 330 off Brazil in June 2009 demonstrated, airplanes large and small are equally subject to the violence of thunderstorms. Satellite observations of the ocean adjacent to Air France 447 at the time of the accident suggest the airplane flew through an area of extreme convective activity.

Options For The Little Guys
Fortunately, in general aviation, we have a few choices not readily available to the heavy iron. If the weather isn’t too tall, we may be able to climb above it. While that may work if we’re light enough to make the climb, if we have a turbocharger out front and if we have oxygen on board, it may compromise range because of less favorable winds at high altitude. If we can see the weather coming from a good distance away, the more viable option may be to attempt a deviation as early as possible.

Given the choice, we’ll sidestep to the right first, the sooner the better to shorten the off-course distance. Thunderstorms and other snockly weather are low-pressure zones with counterclockwise rotation (in the Northern Hemisphere), so we try to fly to the right to take advantage of potential tailwinds.

Descend—The Final Option
If that doesn’t work and flying left looks equally dicey, we have only two options remaining: turn back or descend. Practical considerations (read “money”) nearly always influence our decisions. I once had to turn around in a Cessna 421 five hours out over the Pacific en route to Hawaii because of weather. It was a tough choice, made tougher because I was on a fixed-price contract and any additional expense would be mine to eat. I did it anyway. The total cost of the abort (fuel, parking, hotel, meals, car, etc.) came to about $2,000.

Accordingly, I’ve made dramatic descents several times over the Pacific to avoid penetrating CB activity. A descent is a fairly simple solution as long as you don’t mind burning ridiculous amounts of fuel in turbines and flying for what may be hours at a few hundred or a thousand feet above half an ocean. You know there’s nothing to hit on the way down, the wind and turbulence often will dissipate as altitude decreases and you have the confidence of knowing exactly the elevation of the ocean.



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