Aftermath: Too Low, Too Slow

The photograph is haunting, if you know when it was taken.

Most of the upper part of the frame is filled with a bright yellow wing, banked fairly steeply to the right. The flap is down a notch; the aileron too is deflected slightly downward. The lower part of the picture contains a patch of bare ground, three widely spaced hangars and a little group of people who are certainly looking up at the airplane, although their faces are not discernible. The airplane’s heading, judging from its relationship to objects below, is about 300 degrees.

The picture was taken from the back seat of a CubCrafters Carbon Cub, a light-sport cousin of the Piper Super Cub, by a passenger, the father of a Girl Scout whose troop had been invited to see the flight demonstration. It was his first ride in a light airplane. When he snapped the picture, the spin that would take his life and that of the pilot in the seat in front of him had already begun.

The accident took place at a dirt airstrip southeast of Denver. The weather was VFR, but with a gusty wind blowing out of the south; the nearest reporting point, Centennial Airport, 12 miles distant, called it 12 knots gusting to 26.

A number of people, including the wife and daughter of the passenger, witnessed the accident. The most detailed description given to NTSB investigators came from a 350-hour private pilot who watched from the driveway of his house just across the runway. After running up, he reported, the airplane took off southward, directly toward him, from a large open area north of Runway 5/23. It broke ground in 200 feet, made a slight left turn into the wind and climbed steeply. “The angle of attack on climb was significant,” he wrote. “I would estimate [it] to be more than 30 degrees and as much as 45 degrees.” The airplane “hovered” for a moment — that is, its groundspeed appeared to drop to near zero — at a height of 150 or 200 feet.

Then the right wing dropped “sharply” — the photograph was taken — and the airplane descended vertically, turning. It struck the ground not far from where the onlookers in the photograph were standing. At impact, the witness said, the nose was coming up; it was, he guessed, at a 30-degree angle to the ground.

From the description of the airplane seeming momentarily to hover, it appears probable that the Carbon Cub, which like the Super Cub boasts exceptional low-speed and climbing performance and resistance to stalling, maintained 40 knots or so into the wind. The implausible-sounding angle of attack (probably meaning pitch angle) of 30 to 45 degrees makes sense when you consider that the airplane probably stalls at 20 degrees, the wind-aided climb angle could have been as great as 25 degrees, and the witness’s head-on perspective deceptively foreshortened the climb.

The pilot, 49, was a 9,000-hour ATP and United Airlines instructor with 747 and 777 ratings who had flown P-3s and E-3s — reconnaissance types, the latter carrier-based — in the Navy. He had 3,000 hours in Carbon Cubs. Obviously, lack of experience was not the problem.

In addition to witnesses who saw the accident, several others volunteered earlier observations of the pilot’s flying, all tending to create an impression of ostentatious recklessness — though the low-speed capabilities of the airplane are such that its maneuvers might look reckless even if they weren’t, and these testimonies were offered with benefit of hindsight.

A woman had been driving southward on the road alongside the airport the previous day when she saw the bright yellow airplane turning so low that she thought it had crashed. She stopped and turned back to look for it.

Another witness of the same flight the previous afternoon related that “the pilot would fly directly into the wind and then hold the plane completely still in the wind; it looked like a helicopter at times. ... He would then point the nose of the plane straight up so that the plane was at an almost 90-degree angle to the ground. ... He would hold that position for a second or two and then roll the plane aggressively over to the right or left, heading straight for the ground. He would then swoop up, circle the air park and perform the same maneuver again.”

An International Aerobatic Club-trained judge with 1,200 hours of aerobatic experience reported seeing the pilot “doing departure stalls at approximately 200 feet agl. Some of the stalls were downwind, after doing downwind takeoffs on Runway 22 (sic). The nose was in excess of 45 degrees nose up. The wind conditions were very gusty. I considered this to be extremely careless and reckless.”

A fourth pilot, using remarkably similar language and a similarly indignant tone, reported seeing the pilot the previous day “doing downwind departure stalls at 200 [feet].”

A departure stall is one performed while climbing at takeoff power. It may not be clear why a downwind departure stall would be any different from an upwind or crosswind one — when instructors and students perform these maneuvers at 3,000 feet agl, they pay no attention to the wind direction — but things are different close to the surface.

Because of friction with the ground, wind speed typically increases rapidly with altitude between zero and, say, 1,000 feet. A steady change in speed is called a “wind gradient,” while a marked shift in wind speed over a short vertical distance is called a “wind shear.” When an airplane is climbing downwind through a wind gradient or across a wind shear, the increasing speed of the tailwind manifests itself as a reduction in both climb rate — because some power is being used to accelerate in order to keep up, so to speak, with the accelerating wind — and climb angle. If the airplane is on the back side of the power-required curve, as it is when performing a departure stall, it is unable to accelerate, and an increasing tailwind — or a gust from behind — registers as a drop in indicated airspeed.

Dropping below the stalling speed is not the same thing as stalling, which is a matter of angle of attack, not speed. But a stall will ensue if the pilot does not get the nose down very promptly, because the airplane will start to settle and its angle of attack will increase.

So the reason it might be considered “extremely careless and reckless” to perform downwind departure stalls at low altitude — apart from Part 91’s prohibition of “abnormal attitudes” below 1,500 feet — is that, if a strong enough wind gradient exists, the airplane may stall unexpectedly; it may take longer to regain flying speed; and it may lose more altitude than usual in the process.

These “downwind departure stalls” had been performed the day before the accident, and so the mention of them serves mainly to illustrate the witnesses’ contention that the pilot was in the habit of performing excessively bold maneuvers at excessively low altitudes. When the accident took place the airplane was flying upwind, not downwind; but a similar principle can be said to apply in gusty conditions. A sudden decrease in headwind has the same effect as climbing downwind through a wind shear, and a sudden change in wind direction can turn coordinated flight into a sideslip. In any case, performing extremely low-speed maneuvers close to the ground in a gusty wind is not something a cautious pilot would do.

You get pretty good at handling an airplane when you have 3,000 hours in the type, but even highly skilled pilots make mistakes. The semantics of description will always be slippery. If this accident had taken place during a sanctioned airshow, it would have been counted as a chance mishap; because it occurred during an impromptu display — albeit of a kind the pilot had apparently practiced many times — and with a casual passenger, it was “excessive and unsafe maneuvering.”

Sometimes, a mishap is the only difference between recklessness and virtuosity.

Whatever else you may call it, however, it was an unambiguous tragedy for two families.

This article is based on the NTSB’s report of the accident and is intended to bring the issues raised to our readers’ attention. It is not intended to judge or to reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory.

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, "Technicalities" and "Aftermath," with FLYING readers.

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