Wire strike

By David Jack Kenny

Their ability to get in and out of incredibly constricted spaces is one of the most useful attributes of helicopters, enabling them to carry out assignments that just aren’t feasible in any other kind of aircraft. From emergency rescues to external load hoists and powerline rigging, vital if nerve-wracking jobs depend on a pilot’s skill at putting the aircraft into spaces just barely larger than itself. Of course, doing that successfully depends above all on avoiding obstacles fixed-wing pilots rarely have to think about except during forced landings. Trees, buildings, and cliff faces all claim their share of rotorcraft, but the most common threat is also the least visible and consequently the deadliest. All the cables, static lines, guy wires, and assorted power and signal conduits that crisscross the country—some active, some abandoned, and most of them unmarked—pose the single greatest hazard to pilots, crew, and passengers who need to take off or land someplace other than an airport.

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About 6 p.m. on May 24, 2013, a Robinson R44 was destroyed when it hit powerlines near Cross Timbers, Mo. The 32-year-old pilot and his 21-year-old passenger were both killed; fire consumed most of the wreckage hours before rescuers located the site. The helicopter had taken off from the Lucas Oil Speedway near Wheatland about half an hour earlier on a sightseeing flight; it was owned and operated by the company, of which both pilot and passenger were employees.

The flight departed from a designated landing zone near the track. According to the landing-zone manager, the flight was only expected to last 20 minutes; when it hadn’t returned after 30 minutes, he tried to reach the pilot by cell phone. Calls to other possible stopping points turned up no trace of the aircraft, and it was declared missing around 9 p.m. A search-and-rescue team finally found the site in deep woods at about 1:30 a.m.

One witness saw the helicopter apparently land in a field, then take off again and transition to level flight. He did not estimate its altitude. Investigators found a broken powerline trailing from a pole to the accident site; transfer marks matched the yellow paint of the main rotor blades. At the point of contact, it would have hung about 65 feet above the ground. It was not marked, and was too low to have been shown on the sectional chart.

The pilot had almost 2,000 hours of flight experience, including more than 900 in that specific helicopter. According to company contacts, he preferred to maintain at least 300 feet agl whenever clouds didn’t require him to stay lower–a good practice given that obstacles rising more than 200 feet agl are supposed to be marked. The skies that day were clear. It’s not known why he decided to land, if in fact he did. It might have been for passenger comfort–earlier that day another passenger had gotten sick in flight–or to get a closer look at something interesting on the ground. The witness’ sketchy description might be consistent with a normal takeoff profile, accelerating while remaining outside the shaded areas of the height-velocity diagram. NTSB photographs of the cable show a stranded wire the color of rust, perhaps half an inch in diameter. Unless the pilot noticed the poles, it would have been impossible to see.

Robinson R22 and R44 helicopters are subject to special training requirements defined in Special Federal Aviation Regulation 73. Many operators satisfy some of those requirements by showing their pilots a safety awareness film prepared by Frank Robinson, their inventor. He takes pains to point out that wire strikes are the single most frequent cause of fatal accidents in his creations, and admonishes the viewer to “always assume there are wires.” Not seeing them doesn’t mean they’re not there.