Flap distraction

December 1, 1992

Unfamiliarity with an aircraft is one of the primary causal factors in accidents. Distraction could run a close second, but it's difficult to document. The AOPA Air Safety Foundation's accident database is brimming with records of pilots with low time in type who get into trouble. The accident frequency curves show a very high involvement when the pilot has fewer than 200 hours in a particular make and model. The lower the time in type, the greater the risk. If you and the airplane have survived a long courtship together, the odds of the marriage running a happy course get better — not perfect, but better. A strenuous initial check-out should uncover most of the airplane's idiosyncrasies, so there will be no surprises when you really may not have time for any.

Having time to perform the important tasks is also important. We all have the same amount of time available to us, but how one uses it can make the difference between an uneventful flight and one that provides material for remedial discussion later. Combine low time in type with distraction from the essentials of flying, and you have the basic ingredients for a mishap.

A pilot I know very well was returning from a business trip in an elderly but impeccably maintained Beech Debonair. Fatigue may have been a small factor, as it sometimes is after a long flight. The weather was excellent VFR, and at least four other Saturday-afternoon fliers were in the pattern of the uncontrolled destination airport.

The mix of traffic was typical for the airport, with several fixed-gear singles and one taildragger. Speed differences on final were running 20 to 30 knots, which had caused the pattern to become elongated.

The flap switch on this Debonair is a three-position control: Up, center Off, and Down. An interlock on the switch must be pulled out before selecting Up or Down. With no flap indicator and no preselect function, a look at the trailing edge of the wing is needed to see if what you asked for was what you got. When the switch is moved to the Down position, the flaps will go to full down unless the switch is repositioned to Off at the desired intermediate setting.

While that is an exhaustive description of a simple system, it has a definite bearing on the events as they unfolded. Sometimes, it's the little things that get you.

The pilot entered the pattern on the downwind leg a little high and fast. Time for the before-landing check and to set the flaps at 10 degrees. The CTAF was fairly buzzing with people announcing their positions at several airports in the region. The Warrior on downwind, ahead of the Debonair, was number three for landing.

It was at the height of all this activity that one of the primary laws of aerodynamics asserted itself. Wolfgang Langewiesche wrote, in Stick and Rudder almost 50 years ago, about the flying instinct. A pilot can sense an impending stall by such items as sound, the softness of the ride, mushiness in the controls, and other seat-of-the-pants indicators, Langewiesche said. The Bonanza pilot was experiencing it. This decreasing sense of buoyancy, as Langewiesche calls it, alerted the Debonair pilot to look at the airspeed indicator, which was rapidly winding down to 60 knots rather than stabilizing at the desired 80. The attitude of the aircraft was proper for flaps 10, the power was correct, but the flaps were full down. He had forgotten to return the flap switch to Off when the flaps had extended 10 degrees. So they deployed fully. It was a simple and potentially lethal mistake.

The stall, had it occurred, would have been unexpected because the aircraft was not in the exaggerated nose-up attitude that we frequently see in training, and the pilot was genuinely distracted by looking for traffic. The element of surprise, coupled with torque from partial power and an almost certain delay in response, could have led to the Debonair plunging to the ground quicker than you can say "incipient spin."

The NTSB would have given the probable cause of the accident as "failure to maintain airspeed." But the real cause would have been distraction, a design-induced error of which the pilot was aware, and lack of familiarity with the aircraft due to low time in type. Given the lousy record of pilots new to their aircraft, I had nearly taken the bait. This pilot learned a lesson.

It is a virtual certainty that, if we've just checked out in a new type, distraction will be lurking nearby. It takes time to investigate an airplane's particular control response, flight characteristics, qualities, and quirks. The time to do that is when our attention is focused on learning, not when it's drawn to other tasks.


See also the index of "Safety Pilot" articles, organized by subject. Bruce Landsberg is executive director of the AOPA Air Safety Foundation.