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Flying Carpet

Runaway autopilot

Years ago when I instructed part-time in Indiana, my instrument student Pete surprised me with an opportunity to fly for his company. “We’ll start with rental airplanes while you help pick out a suitable twin,” he said during a lesson. Having only 140 hours of multiengine experience at the time, I asked why he chose me.
Flying Carpet
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Greg Brown flew both corporate and airline stints before returning full time to personal aviation.

“As an instructor you are thorough, cautious, and safe,” said Pete. “You’ll need a type-specific checkout and we’ll initially pay a higher insurance premium, but those are good investments in my opinion.” I took the job, and ultimately we purchased a cabin-class Piper Navajo.

My first lesson was how much work it takes to run a single-airplane corporate flight department. I spent more time managing maintenance and logistics than piloting. For one thing, radios were less reliable back then, meaning frequent visits to the avionics shop. Then one day the landing gear wouldn’t retract after takeoff. Flying the normally speedy twin home from the East Coast at the 130-knot maximum-gear-extended speed was memorable for the wrong reasons.

On the airplane’s first annual inspection under our ownership, our mechanic found the pitch trim out of limits. After he corrected it to factory specs, I could no longer trim the nose down adequately and had to manhandle the yoke to descend. Resetting trim to the factory’s maximum forward limit didn’t solve it. After much hemming and hawing, a factory engineer finally admitted off the record that the published trim specs for our model were wrong. He confidentially advised me that “many owners choose to unofficially set the trim in the range where it actually works.”

This airplane featured a curtained, plastic-bag-lined toilet in the aft cabin that happily no one ever used. (My pilot duties included cleanup.) An associated “relief tube” evacuated urine via funnel, hose, and under-fuselage venturi, where it vaporized outside the aircraft. This device proved handy on extended flights.

Pete usually accompanied staffers on longer missions, so we took turns covering the controls when nature called. But one day after dropping employees at Boston, I found myself returning five hours home alone. After sipping coffee early in the flight, I realized I’d forgotten to bring a relief bottle. Landing would cost an hour, and being eager to get home I initially determined to tough it out. But as pressure grew, I couldn’t help but contemplate entrusting the airplane to autopilot and hurrying aft to the relief tube. That would be stupid, but with each increasing degree of discomfort my risk assessment skewed further toward, “heck, it would only take a minute.”

Finally, cruising clear and empty Ohio skies on autopilot at 180 knots, I could wait no longer. As I reached to unbuckle my seatbelt, the airplane abruptly pitched skyward. It was all I could do given the associated shock, speed, and G forces to regain control before going vertical, disconnect the autopilot, manage power, and wrestle the big twin’s nose back down. Had it happened a moment later I wouldn’t be here writing this.

Afterward the avionics folks could not reproduce the anomaly; the autopilot worked fine for extended periods with the occasional sudden pitch-up to alarm my passengers. Over many attempts the techs determined that the autopilot trim servo was improperly trimming the airplane nose-up in level flight, making the pitch servo battle it to maintain altitude. On longer flights the latter would ultimately overheat and cut out, releasing the nose upward. Once it cooled, however, the autopilot would again operate.

I don’t remember how I addressed nature’s call following that long-ago runaway autopilot—an empty pop can might have been involved—but needless to say, I have never again considered leaving the controls without another competent pilot to cover them. Oh, and I always carry a relief bottle.

Greg Brown
Greg Brown
Greg Brown is an aviation author, photographer, and former National Flight Instructor of the Year.

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