Safe Flight's device warns of 'hot' power lines

 - May 27, 2008, 7:14 AM

After three years of development and testing, Safe Flight Instrument’s “Powerline Detector” system for helicopters received FAA supplemental type certificate approval last month. The approval applies to the White Plains, N.Y.-based company’s own Aerospatiale Gazelle, and STCs for other helicopters will be sought as customer needs dictate. The first customer for the power-line detection system may be the Swedish air force, which is considering the device for its fleet of 12 Eurocopter Pumas. Schweizer Aircraft is considering the system as an option for its helicopter models and the U.S. Army evaluated the system for its Bell TH-206 training helicopters.

Using an extra-low-frequency receiver, the Safe Flight system detects power lines by measuring the electrical energy they radiate. Consequently, only active “hot” power lines are detectable, leading a company spokesman to characterize the device as a “live-wire detection system.” When the intensity of the field exceeds a preset value, the system illuminates a warning annunciator and sends a Geiger counter-like pulsed signal to the pilot’s headset and illuminates a warning light on the system’s control panel. If the aircraft flies closer to the power lines, the signal increases in frequency.

The greater the electrical power in the lines, the farther away the system will detect them. For example, the system will detect large three-phase high-voltage lines at about 1,500 to 1,800 ft. Single lines carrying lower voltage trigger the warning at about 800 ft. The system does not provide an indication of the location of the electrical source with respect to the aircraft nor does it differentiate between types of power lines.

Weighing only eight-tenths of a pound (not including the external antenna), the basic unit measures 5.51- by 2.4- by 1.55 in. and is designed to mount in the instrument panel. The control panel consists of a sensitivity rheostat switch, an annunciator light, which also functions as a mute button to turn off the audible warning, and a green power-on light. Adrian Rosenberg, Safe Flight helicopter pilot and assistant engineer, told AIN the sensitivity switch was added after early testing showed that flight over populated areas triggered warnings nearly the entire time when the aircraft was at low altitudes. A cyclic-mounted mute button is available as an option.

Although two antenna installations were tested–a nose-mounted bent-whip antenna and a fuselage-mounted HF antenna–only the latter was certified. The basic price of the system is $9,500, not including installation, which Rosenberg estimated would take about two days.

Demonstrating the Powerline Detector system to AIN last month in the company’s Gazelle, Rosenberg flew near and over a variety of power lines in northern New Jersey, being careful to stay outside New York City’s enhanced Class B airspace. With the helicopter at an altitude of about 500 ft agl, the system began issuing its audiovisual warnings of a three-phase power line when it was about a quarter-mile away to the left.

The clicking of the aptly described Geiger-counter audio warning in the headset was unlike any other cockpit warning and instantly noticeable. As Rosenberg flew the Gazelle toward the power line, the clicking increased in frequency until it reached a rapid pulse, holding at this level until the power line passed beneath the helicopter. With the line behind the helicopter, the clicking frequency decreased. The annunciator displayed warn in red whenever the audio clicked.

Over a small town with a normal array of power lines, the system clicked incessantly until Rosenberg decreased the sensitivity of the receiver. He said it takes some practice to get the sensitivity set at a level that eliminates unneeded warnings yet still catches potentially serious ones. He demonstrated the mute button, which worked, silencing the clicker. The annunciator lamp displayed mute in yellow with this function engaged.


There are two main limitations of the Safe Flight power line warning system, in AIN’s estimation. The first is its inability to provide a direction to the source of the warning. It was easy to imagine flying low level along a valley in a low-visibility condition, not an uncommon situation for many helicopter operations, and hearing the Geiger counter go off in the headset. There’s no way of knowing if the detected power line crosses the valley directly in front of the aircraft or is converging from one side, or even if there are multiple lines.

On the other hand, if the warning were combined with another source of information, such as a moving map or chart depicting the location of known power lines, one’s confidence level would increase significantly. Detection of non-charted power lines would be an added bonus.

The second limitation is that the Powerline Detector is only a live-wire detection system. “Dead” power lines, non-powered cables, guy wires stabilizing poles and towers and other obstacles are not detected. As Safe Flight puts it in writing, the system “does not warn against all power lines and will not alert pilots of some strike hazards that emit electromagnetic fields.”

However, if the pilot flies with these limitations always in mind, Safe Flight’s Powerline Detector could provide an extra margin of safety that will help avoid an unpleasant encounter with a hot wire. Given the system’s light weight and relatively low cost, it may well end up as a standard safety item on many helicopters.