The wind was blowing out of the south, 23 knots gusting to 27, when the 172 touched down on Runway 14. The crosswind was about 40 degrees. A pilot on the ground, using a handheld radio, was at the approach end of the runway giving wind advisories to a group of airplanes returning from a nearby Sunday morning fly-in. He watched as the 172 touched down “a little too much tail low for the wind, I thought, but still on the grass part of the runway.” (The runway, about 3,300 feet long, had a 22-foot-wide band of blacktop in the center of a 100-foot-wide grass strip.)
“I believe all three wheels were down and he was safe,” the witness reported. “Then he called to say he was taking off again to do the landing over.”
The pilot on the ground watched the 172 until it was airborne, then turned away. When he looked back down the runway, “…to my amazement [the 172 pilot] … was in a tight power turn into a left downwind and stalled at about the 180-degree point, at about 200 feet high.”
Another witness reported the wingtips “rocking up and down about 10 degrees off horizontal as its fuselage tilted up and down about 10 degrees off horizontal.” He said that as the airplane approached a grove of trees its altitude increased to about 200 feet, and as it began to level off the right wing rose perpendicular to the ground and the airplane nosed straight down.
The airplane came to rest in flat pastureland about 1,500 feet northeast of the airfield. The ground scar indicated that the airplane was heading about 344 degrees when it struck the ground. It was destroyed and the 240-hour private pilot and his passenger were killed. There was no indication of a mechanical problem; the engine, which had undergone a 100-hour inspection 12 hours before the accident, was in good condition, and gouging and bending of the propeller indicated that it had been turning on impact.
The National Transportation Safety Board’s finding of probable cause was straightforward: “The pilot’s failure to maintain adequate flying airspeed during the climbing left turn resulting is a stall condition. Contributing factors were the gusty crosswind conditions, and the pilot’s excessively tight turn maneuver during the initial climb.”
This accident is typical of a class of mishap lumped under the heading of “downwind turns.” A downwind turn is one in which the airplane turns from a heading into or across the wind to a heading on which the airplane and the wind are moving in approximately the same direction.
Much has been written here, a good deal of it by me, about the physics of downwind turns. Despite it all, many pilots refuse to budge from the belief that turning downwind is dangerous because the airplane is bound to lose airspeed in the process. They support their opinion by pointing out that many airplanes do, in fact, crash when turning downwind.
(One should not to grouse too much about failing to persuade-why should one zealot bow to another?-but I was disheartened recently when a reader, writing to congratulate Richard Collins on a discussion of downwind turns, closed with the remark, “Now if we could just convince Garrison.” Since my views and Dick’s on the matter are, as far as I know, identical, I felt as Pat Robertson would if he were reproached for too fanatical an advocacy of gay rights.)
The unfortunate thing about the zombielike persistence of the physics dispute is that it distracts pilots from what they should really understand about downwind turns. This accident is illustrative; it is apparently a “downwind turn” mishap, but on closer examination it reveals aspects unrelated to the turn, aspects that could have caused an accident even had the wind been calm.
The first thing to note is that when the airplane stalled, it was no longer turning. The wings were at least momentarily level and the airplane had reached the downwind heading.
The second thing to notice is that the pilot reached the downwind leg at an extremely low altitude and quite close to the runway.
The third is that the normal pattern for the airport, where the pilot had landed many times before, was a right hand pattern, but the pilot turned to a left downwind leg.
It seems that the pilot was dissatisfied with his first landing and decided to have a second try, not because he had to-the first had apparently brought him safely, if not elegantly, to earth-but because he wanted to show himself or others that he could do better. Both the steeply banked “power turn” close to the departure end of the runway and the fact that the turn was to the wrong side suggest a somewhat impulsive style of flying. The left turn was especially unfortunate because it made the airplane vulnerable to gusts from behind while it was still at a low altitude; a right turn would initially have put the wind more on the nose, giving the airplane more time to gain altitude.
To the extent that downwind turns have special dangers, it is only when they take place at low altitude. The first difficulty is the visual disorientation experienced when flying in a strong crosswind near the ground. The airplane seems to be sliding sideways, and one is tempted either to bank more steeply into the turn or to step on the inside rudder in order to “catch up” with the airplane’s apparent motion. The only reliable way to stay coordinated in a turn across a stiff wind is to consult the inclinometer ball.
The second difficulty has to do with wind shear. Wind speed sometimes increases rapidly with height above the ground. An airplane climbing downwind through the gradient will experience lagging indicated airspeed and a loss of climb rate. The magnitude of these effects depends in part on the airplane’s rate of climb and ability to accelerate under power, and in part on the steepness of the wind gradient. A climbing airplane has little excess power available for accelerating, especially if it is banked; and so the way to keep up with an increasing tailwind is to lower the nose, temporarily sacrificing rate of climb, and to reduce the angle of bank. This is a natural enough reaction to sagging airspeed, but when both airspeed and rate of climb sag simultaneously, a pilot close to the ground may become confused about how to react.
The witness’s mention of the airplane’s altitude increasing as it approached a grove of trees suggests an updraft that could have pushed the airplane abruptly into an accelerating flow. It’s important to realize, however, that losing indicated airspeed is not the same thing as stalling. As long as the angle of attack is below the stalling angle, the wing will not stall regardless of the airspeed. But the pilot must push the nose of the airplane down when the airspeed drops; otherwise the airplane will begin to settle of its own accord in a flat attitude, increasing the angle of attack of the wing and then, perhaps, producing a stall.
The apparent impulsiveness of the decision to make a second circuit may have clouded the pilot’s judgment. Under conditions of strong gusty wind, safety requires a few sensible precautions.
The fundamental requirement is an airspeed cushion roughly equal to the variations in wind speed. It may not be possible to hold the airplane on the ground in a crosswind once it has reached flying speed, but after lifting off the airplane should be turned into the wind sufficiently to keep the ground track aligned with the runway. The initial climb should remain shallow for long enough to establish good climbing speed plus a cushion; usually just a few seconds’ delay is sufficient.
The initial climb should be straight ahead to an altitude of at least 200 or 300 feet before starting a crosswind turn. (An extended initial climb in a strong wind is advisable anyway, just to keep the pattern the right shape and in the right position.) The angle of bank should be moderate, and it’s important to keep an eye on both airspeed and coordination, but not to focus your attention on the ground. In fact, a climbing turn in a strong following wind, like a night takeoff over unlighted terrain, should be handled as an instrument rather than a visual-reference maneuver.
Level the wings for several seconds on the crosswind leg to assess your position in the pattern. If the wind is across the runway, you may need to adjust your turn to the downwind leg inward or outward to maintain the proper distance. Be aware, too, that because of the wind other traffic may have drifted out of position, and an airplane that took off after you but turned sooner may end up ahead of you, or coming up from below, on the downwind leg.
Having laid out all these cautions, I wonder if it’s not best for pilots, or at least some pilots, to go on believing that a downwind turn is inherently dangerous because it necessarily involves a loss of airspeed. This is factually false and implies a misunderstanding of the relationship between the airplane and the air. But if it instills fear and concentrates attention, perhaps the myth of the downwind turn ought to be allowed to survive on the grounds that it does less harm than good.
This article is based solely on the National Transportation Safety Board’s report of the accident and is intended to bring the issues raised to the attention of our readers. 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.
