The wires you do not see

Helicopters have a higher risk for wire strikes because of the way they are flown. A helicopter’s unique capabilities lend it to the type of work often requiring low-level flight over unknown terrain, such as picking up an accident victim or slinging buckets of water to fight a fire. Wire and object strikes comprise the top operational cause of fatal helicopter accidents, and it’s a sobering thought to know that two fatalities occur for every five wire strikes. Studies have shown that although flight experience can lower risk in many aspects of flight, there is no statistical difference regarding wire strikes between high-time and low-time pilots. Wires are hard for everyone to see.

Back in the 1980s flying power line patrol, you would think I would have been a wire avoidance expert, flying about 1,500 hours a year at an altitude no higher than 300 feet. But just as the data show, experience is not an asset for avoiding a wire strike—which I almost proved one day.

A local TV station was doing a feature about flying helicopters on power line patrol, and I had just landed in a small field to meet them. There were no hazards, except for a small telephone wire at the opposite end of my approach. An hour later the cameraman asked me to depart in the other direction from the approach, and it was during takeoff I suddenly remembered that little wire. Instantly adding more power with an aggressive cyclic climb, I finally saw the wire zipping underneath about five feet, followed by a man that was stupid, I’ll never do that again moment. I had changed my planned departure path without careful thought and another reconnaissance of that area.

An average of 76.6 aviation accidents per year in the United States involve wires or power lines, according to a 2010 FAA Safety Alert for Operators.Techniques helicopter pilots use to avoid wire strikes include thoroughly assessing an area from a higher altitude, realizing the wires not seen are most dangerous. Scan for easier-to-see poles and towers, and don’t assume there aren’t extra wires splitting off in a different direction. Try to make the departure path the same as the approach path; no hazards on approach dictates you should be clear on departure. The more eyes the better, so use people onboard, having all crew and passengers with “eyes outside” looking for any hazards. Private helipads should be treated as carefully as off-airport areas, as they do not offer the same assurances as public helipads or airports. Wires adjacent to a private helipad do not require marker balls, nor do towers less than 200 feet have to be lighted. Picture landing at an unfamiliar hospital helipad at night, with an unlighted 190-foot communication tower 250 feet away.

Helicopter terrain avoidance warning systems and sectional charts, while useful for en route flight at safe operating altitudes, can be of limited use when operating low level as obstacles lower than 200 feet are not included in the database. A safe en route altitude is dependent on the area flown, but many would consider 500 feet to be a minimum for onshore daylight conditions. Avoid “getting squeezed”—deteriorating weather can reduce the available altitude, resulting in a lower cruising altitude and increasing the risk for a wire strike. Power line detection systems are effective but only detect energized lines. Support wires, guide wires, zip lines, ropes, and some tramlines are not energized and so do not produce an electromagnetic field that can be detected. A wire strike protection system, which typically can cut a steel cable up to three-quarters of an inch, also has its limitations. It doesn’t provide 100-percent frontal coverage, and it’s dependent on the helicopter flying at least 30 knots at no less than a 60-degree angle to the wires with no more than plus or minus 5 degrees pitch attitude. All these systems certainly lower the risk of a wire strike, but the best wire strike deterrent is the pilot.

It isn’t the wires you see that will kill you, but the ones you don’t see.

Markus Lavenson is a captain in the Sikorsky S–92 and Leonardo Helicopters AW139 flying oil and gas support missions in Alaska and the Gulf of Mexico.