By David Jack Kenny
On Aug. 5, 2013, the 34-year-old pilot of an Air Tractor AT-400 became at least the fourth crop duster in the past few years killed when his airplane collided with a meteorological tower. This time the accident site was in the southeastern corner of the Oklahoma panhandle, but key details of the tragedy were similar to those of earlier crashes in Texas and California. The towers in question were placed in remote agricultural areas to evaluate prospective sites for wind farms—and all were just under 200 feet tall, thereby avoiding the FAA’s requirement that they be marked and lighted as potential hazards to aerial navigation. All four collisions happened in good visibility in the daytime.
The Air Tractor’s pilot held a commercial certificate for single- and multiengine airplanes. According to his employer, he had about 1,750 hours of career flight experience, including around 600 in the AT-400. On the morning of the accident, he’d taken off from a private strip with about 100 gallons of fuel and 200 gallons of herbicide. A property owner in the vicinity recalled having seen the accident airplane make frequent flights over the area, including several earlier that morning. A witness operating a road grader about half a mile away saw the Air Tractor fly straight and level into the tower at an altitude he estimated as 150 feet agl—a guess confirmed almost exactly by the airplane’s on-board GPS data logger.
Unlike those in the earlier accidents, the Oklahoma tower wasn’t completely unmarked. Its owners had gone to the trouble of painting its upper third in alternating white and orange bands. But at the time of the accident, the airplane had been flying almost directly toward the sun, making the slender structure nearly impossible to see. The right wing of the Air Tractor hit it squarely in one of the orange sections about 35 feet from the top, shearing off the wing’s outermost seven feet and throwing the airplane into the ground inverted. A 350-foot ground scar littered with aircraft parts led to the main wreckage.
The NTSB, the National Agricultural Aviation Association, and the FAA—among others—have drawn attention to the hazards meteorological towers pose not only to crop dusters, but to EMS, firefighting, and law enforcement flights. NTSB recommendations and FAA guidelines on marking structures below the 200-foot threshold remain voluntary, and this accident shows that even good-faith efforts to comply with their recommendations don’t guarantee that those structures will always be seen. In the end, the best defense available is the one routinely used by instrument pilots: Choose altitudes where there’s nothing else to hit.
Time is money, and fuel is more money, and margins are tight in almost every kind of aerial work. But unfulfilled contracts are also bad for business, while wrecked aircraft are ruinously expensive and lost lives beyond price. Flying at altitudes where obstacles must be marked and charted might add another minute to each leg—30 seconds in climb, 30 more in descent. Two hundred feet is also the threshold for depicting obstructions in many GPS terrain databases, raising the possibility of a life-saving alert. If cruising at 500 feet agl seems too wasteful, operators might at least require their pilots to climb to 300. It seems like cheap insurance.
FAA Advisory Circular 70-7460-1K, "Obstruction Marking and Lighting"
"Surviving the wires environment" video
"Emergency Procedures" Safety Advisor