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Too slow, too lowToo slow, too low

CEN10LA031CEN10LA031

By David Kenny

Student pilots are drilled on slow flight, stall recovery, and spin avoidance throughout primary training, and for good reason: Understanding how the airplane handles at minimum controllable airspeed is a crucial survival skill. So is being able to feel an incipient stall. An inadvertent stall chews up more altitude in some airplanes than others, but it always uses some. If an uncoordinated stall develops into a spin, “some” is likely to be a thousand feet or more—one of the principal reasons that spin accidents are fatal more often than not.

It’s drummed into students before they’re ever signed off to solo. It’s tested on the private and commercial checkrides, and brought up on every meaningful flight review. And still, every year, pilots decide to motor along at low speed close to the ground. Many are experienced enough to know better. Some make the further mistake of trying steep turns—to look at something below, perhaps, or avoid unexpected obstacles—and pay for it with their lives.

On Oct.27, 2009, an Aeronca 7AC Champ spun in next to Interstate 75 in northern Michigan, narrowly missing a car driven by two off-duty state troopers. Both the 52-year-old pilot and his passenger died from their injuries despite the efforts of the troopers and several other passing motorists, including a nurse. Fuel poured from the ruptured tank onto the airplane’s engine, but never caught fire.

The troopers were among six witnesses who had seen the airplane flying very slowly just above the highway. Estimates of its altitude ranged from 60 feet to 300 feet. The troopers described the airplane making a series of “very abrupt” right turns—one suggested that the pilot might have seen elk and was going back for a closer look—before suddenly rolling right and corkscrewing into the ground. The other witnesses confirmed the abrupt, nose-down descent, and a GPS unit recovered from the wreckage showed the aircraft slowing from a groundspeed of 68 knots to 44 kt. The markings on the Champ’s airspeed indicator showed a power-off stall speed of 42 knots, and the witnesses agreed that winds were calm at the site.

The troopers also noted that traffic on the Interstate was light at the time, and the grass median was unobstructed. One commented that “at no time did it appear as if the plane was trying to land,” and the condition of the prop suggested that the engine was running at the moment of impact.

The pilot claimed more than 2,800 hours on his last medical application and held ratings for airplane single-engine land, single-engine sea, multiengine land, and instrument airplane. He had bought the Champ, a 1946 model, in August 2007 and had it completely restored, a process that took nearly two years. It received a replacement airworthiness certificate at the end of May 2009. An oil change was done 15 hours later, just four days before the accident; this was the last maintenance work recorded on the airplane. The pilot’s logbook was not recovered, and his make-and-model experience wasn’t reported.

The pilot’s experience with accelerated stalls is likewise unknown—especially his recent experience, and more specifically his recent experience with accelerated stalls in the Champ. Perhaps he’d carefully explored the corners of the flight envelope at altitude before taking a passenger sightseeing just above the treetops. But if not, he wouldn’t be the first pilot who came to grief after forgetting that stall speed varies with the aircraft’s weight and attitude, and is usually higher than the wings-level minimum shown in the book (and on the airspeed indicator). Unfortunately, he probably won’t be the last.