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Winging It! With Dr. Paul

Gemini

"But you were born under the sign of the twins," observed the First Lady's astrologer at the fashionable Washington cocktail party. "How come your pilot certificate says ASEL?"

"I never went in much for that 'safety in numbers' crap," I replied, seeking refuge in the crowd. Much later, upon reflection, I realized it was far more complicated than that.

Consider the probabilities. Mind you, modern aircraft engines are comfortingly reliable. Yet each has a finite life. The fan up front, it's said, is there only to keep the pilot cool. If you don't believe it, let the fan stop in flight, and watch the pilot start sweating.

TBO tells only half the story. We know, on the average, how long a properly maintained and flown engine can be expected to last. But individual engine lives are distributed about the mean. Even a well established variance does little to assure us a failure-free operation. The distribution tells us only how frequently engines fail, not when this particular fan will cease keeping us cool.

What has this to do with multiengine flight? Simply this: every operation carries with it a finite probability of an engine failure. Whatever the exact numbers are, and slim as the likelihood of failure might be, when you hang a second engine on the airframe, that probability inevitably doubles.

Engine failure odds in a twin are a little like the frequent flier in fear of terrorist attacks. Required to fly often on business, he asked his chief statistician the odds of a bomb being placed aboard a particular airliner. The statistician, dividing the number of bombings by the number of flights, came up with comforting odds: one part in ten to the sixth, or a million to one.

Those are reasonable odds, but our friend was not reassured. What chance, he asked, of two bombs aboard?

Unprecedented, you say? Well, you're right, but the magic of mathematics is that it provides precise answers to meaningless questions. One in ten to the sixth, squared, is one chance in ten to the twelfth. A trillion to one against. Our traveling executive liked those odds quite a bit better, and thereafter always carried a bomb in his baggage on every trip.

So I trust the odds, and fly singles. In a twin, I'd have to play it safe by always caging one engine before takeoff, lest two fans fail in flight.

But what do you do when an engine actually does fail? In a single, it's pretty obvious. You land. Not so simple in a twin; you have a decision to make, and if close to the ground, quickly and correctly the first time. Now, what are the odds of making the wrong call? Pretty good, if the accident statistics are to be believed. For many light twins with one engine out climb about as well as a single with one engine out.

Only it's worse than that. We read all the time about pilots feathering the wrong fan, or rolling over beyond recovery from adverse yaw, or just plain flying it into the ground while trying to cope with an engine out on the gauges. Not that they haven't learned the right procedures, but how many of us have an opportunity to actually practice them, once the checkride is behind us? The very risk makes meaningful recurrency training untenable in a twin, save in a simulator. And few outside of the airlines or the military receive that kind of a workout with any degree of regularity.

Truth is, the very skills most likely to save your neck when a fan stops spinning are those least often practiced. You don't think twins are riskier than singles? Just look at the insurance rates - there's one industry which does its homework very well, and plays the percentages better than our traveling executive.

My friend Claude, a CFI and fellow Gemini, added a multi rating to his ticket a few years ago. He had some extra income to tax-shelter, and plunked it down on a crash course. Four hours in an Apache, six in a simulator, groundschool and checkride for a cool kilobuck. He's not logged an hour of multi time since. Nobody will rent him a twin. I think the FBOs are in league with the insurance companies. Or maybe they just don't trust Geminis.

That's really why I'll likely never fly twins. It's not in my stars.