Update: Wire Strikes
By William H. Wimsatt
Exposure to wires, antennas or other obstructions to air navigation generally occurs within and around the airport environment for airplanes. For agricultural aircraft they are a fact of life; and wire strikes are the No. 1 cause of helicopter accidents.
Historically, pilots have borne the brunt of responsibility for wire strikes on the rather illusory assumption that pilots can see and avoid wires, towers and all measure of obstructions. Meanwhile, Utility Companies have largely stuck their heads in the sand while keeping a firm finger of blame pointed directly at the Pilots. Yet, the Utilities have always been well aware of Federal Aviation Regulation, Part 77 which sets forth the obstruction standards both around and away from airports; and have known of the need to notify the FAA about constructions or alterations which are more than 200 ft. in height or penetrate any imaginary safety surface of an airport.
But things change, sometimes for the better, and the law presently sees the responsibility for wire strikes as more or less equally shared between the cockpit and the Utility Board Room. The reality of the situation is that wires, and often the towers that support them, are difficult and sometimes impossible to see, even if the general location of the wires is known. Their visibility and the ability to detect and locate them are affected by sunlight, masking terrain and changes in perspective (during climb or descent).
A pilot can mentally draw imaginary lines between towers; and, this can be helpful at times. When transiting an area, it is easy to stay above an imaginary line drawn from tower to tower. But what about landing or working at low altitude in an area where there are wires? Seeing real wires or avoiding imaginary lines are just not a viable solution to the hazard or risk of wire strikes. SPHERICAL MARKERS ON THE LINES ARE!
A visibility expert from the Scripps Visibility Laboratory in San Diego noted that: wires and towers are hard to detect when masked by surrounding terrain; it is impossible to judge distance from a wire, yet the mind will supply missing details and form conclusions, which are not likely accurate; accurate distance judgments can be made from a line marked with spherical colored balls; and, at 60 mph there is less than _ second to detect and avoid an unmarked power line. Whereas at 60 mph more than 20 seconds is available to detect and avoid a marked power line. Few would dispute that marker balls are helpful. Most agree this Is a reasonable way to deal with the wire strike problem.
BOTH THE UTILITY AND AIRCRAFT have a right to use the airspace above the ground. Utilities purchase this right with an easement or right-of-way. Aircraft have freedom of movement within navigable airspace, according to our government, which regulates this airspace.
Helicopters can operate anywhere, even as low as the ground under the regulations governing navigable airspace [14 CFR 91.119(d)]. But a Utility must tell the government before putting up any span of wires more than 200 ft. above ground level [14 CFR 77.11 and 77.13].
The Utility has a right to expect aircraft will operate carefully around their wires, but they also have a responsibility to do what is reasonable to help aircraft avoid those wires. How? Notify the FAA as the regulations require. And, evaluate for marking those wires which are difficult to detect and located where low flying aircraft work. This is the responsibility Utilities share with aircraft to prevent and avoid wire strikes. Both depend on each other for their mutual safety and protection.
In July 1992, representatives from the aviation community, the electric utility industry and government agencies convened as a task force to develop a comprehensive program to improve low level flight safety throughout California. In mid-1993, major California utilities field tested the validity of a wire marking criteria and methodology at about 100 transmission lines statewide. Evaluators included utility engineers, pilots, FAA inspectors and State aviation officials.
After the field evaluation, researchers found a significant degree of consistency in the risk level determinations among all evaluators, regardless of background. Seeking an even greater degree of consistency, the task force revised the guidelines to more precisely focus the evaluator’s attention on two key factors: wire visibility and likelihood of aircraft at the wire’s elevation. In October 1993, Assembly Bill 1017 implemented a statewide program of pilot education and further evaluation of criteria developed for marking wires. The heart of the Wire Strike Education & Prevention Program was the procedure for requesting marking and evaluating a particular span of wires or supporting structure for marking according to established criteria.
Any person could request that a Utility mark a wire or a supporting structure. The Utility was then required to evaluate that wire or tower using the Wire Strike Risk Assessment Criteria. Within 90 days of the request, the Utility was required to notify the requestor whether the wire or tower would be marked. This Wire Strike Education & Prevention law sunset as of 1 January 1996. But, to an extent, this program continues today on a voluntary basis. The Wire Strike Risk Assessment Criteria, still exists in the hands of the electric utility industry in the State of California and likely throughout the United States. The assessment criteria for evaluating wires focus on the two primary considerations that common sense suggests define a hazardous wire location, namely, the visibility or detectability of the wires and the likelihood or foreseeability of aircraft at that location and altitude. It is an effective criteria which is numerically graded, such that the scores are then placed upon a matrix to determine the degree of risk as high, medium or low.
The pilot of a low flying aircraft need only contact the Utility responsible for the wires and report the hazard or ask that they be evaluated for marking. With the Wire Strike Risk Assessment Criteria in hand, the Utility can readily go to the scene and address the hazard posed by any particular span of wires. If it’s low risk, there is no need to mark the wires and the evaluation can be filed as protection against any legal or non-legal future complaints. On the other hand, if the risk is high, the Utility now has both the knowledge of the risk and a reason to place spherical markers on the line in order to do their fair share to minimize that risk.
William H. Wimsatt is a partner of the law firm of Magaña, Cathcart & McCarthy. He is aircraft and helicopter rated and has successfully represented clients in wire strike cases throughout California.
Navigable airspace is defined as "Air space at and above the minimum flight altitudes prescribed by or under this Chapter, including air space needed for safe take off and landing." [14 CFR 1.1] For aircraft other than helicopters, FAR 91.119(c) states, "Over other than congested areas. An altitude of 500 ft. above the surface except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 ft. to any person, vessel, vehicle or structure. [14 CFR 91.119(c)] There are many situations where an aircraft would be within the exception noted in FAR 91.119(c). Search and rescue, police patrol, aerial survey, lake patrol, amphibious operations and patrol search for illegal aliens all require low level operations. Although it might be pointed out that power lines and their supporting towers are structures, the pilot still has to be able to see them to avoid them. That’s where the marking, or lighting at night, becomes necessary.