Business & Commercial Aviation September 2005
Listening for Trouble
B&CA flies Safe Flight Instrument’s Powerline Detection System.
On June 15, 2005, the owner/pilot of a small piston-powered helicopter was returning home to Cherokee County Airport near Jacksonville, Texas, after conducting business in Shreveport, La. Around 8 a.m. eyewitnesses near the small town of Rusk, Texas, watched the helicopter, which was following a highway, descend into unmarked power lines. The little aircraft crashed to the ground, killing the pilot, the 31st civilian to die in five years due to wire strikes in the United States.
Just one week later, the pilot of an ex-military surplus OH-58 helicopter performing a power-line survey struck one of the lines near Graham, Texas. In that encounter, the helicopter was damaged, but the pilot survived with minor injuries. That same week, a Bell 206B struck a residential powerline in Michigan, injuring all four persons aboard the JetRanger.
“Wire strikes are the number one operational cause for helicopter accidents when a collision with objects takes place,” said Matt Rigsby, transportation industry analysis officer for the FAA Southwest Region Rotorcraft Directorate.
All helicopter pilots are taught to respect (if not fear) wires of all types since they’re difficult to detect, especially in low visibility situations, and can easily bring down the most robust helicopter in the sky.
New power industry strategies to make wires less visible to the public by sandblasting away reflectivity or camouflaging them in green, will likely increase the hazard to unwary or unlucky helicopter pilots. Even more disturbing is that this practice of making lines invisible continues in places where they cross highways and roads, which are often the field landing sites for medevac helicopters.
Although laser (see “Laser Wire Seeker” sidebar), infrared detection systems and powerline mapping databases for EGPWS are currently available to improve situational awareness, for many operators this equipment is simply too expensive. And when you consider that most reported powerline strikes take place at altitudes of less than 200 feet, and most of the lower output supply lines are only slightly above tree level, a truly comprehensive powerline database is years away, at best.
So, into that reality steps Safe Flight Instrument Corporation. The White Plains, NY, based company has developed a system that is both affordable and practical for helicopters and crews that operate in heavy wirestrike environments, such as those who fly utility, news, law enforcement, EMS and agricultural operations, along with corporate pilots who routinely fly to off-airport locations.
“Powerline strikes are one of the greatest threats to both civil and military helicopter operations worldwide,” said Randall Greene, Safe Flight’s President and CEO. “A horrific EMS helicopter crash in the mid-1990s led Safe Flight to begin development of a Powerline Detection System (PDS) that would give pilots an audible warning of the proximity of live power lines. Today, we are pleased to have such a product in the marketplace.”
As most wire strikes involve light single engine helicopters, a practical detection system must be lightweight and inexpensive; high-tech laser and radar-based systems are neither. The Safe Flight system is essentially a radio receiver that detects the frequency of the electromagnetic field of the powerline (60 Hz in the United States, or 50 Hz for Europe; the system can be adapted to either). The system picks up the field of energized wires only; it cannot detect non-energized lines, or static lines such as deactivated electric lines or those that support radio antennas. Since the system “hears” the live wire, it is only an aid to situational awareness and no substitute for the Mark I eyeball. Still, for those who fly among wires, any help in spotting them is always welcome.
Looking for Wires
The major components of the Safe Flight PDS are a receiver and display unit, a signal amplifier and an antenna. The receiver/display unit measures about 1.5 inches high by 2.5 inches wide by 5.5 inches deep and weighs about one pound. The unit mounts on a JetRanger’s instrument panel, but its compact size makes it easy to install in a variety of locations within easy reach of the pilot. The display face has a sensitivity knob, a warning lamp/switch that acts as both the warning indicator and mute switch. A small power LED is provided to verify power to the unit. A separate press-to-test switch is mounted nearby on the instrument panel.
The system relies on an airframe-mounted antenna to receive the signal: antenna selection and placement varies by aircraft. On a JetRanger, the antenna is located on the transition section of the aft fuselage just forward of the tail-boom attachment. The antenna is a small whip type and is located just below a communication antenna. Safe Flight is developing a method for sharing existing antennas, thereby making a separate antenna unnecessary. The small signal amplifier is located just aft of the cargo bay on a bulkhead. Additional aircraft wiring is minimal, with one cannon plug for power supply and another for the antenna wire.
The alert function consists of both a Geiger-counter-like tone through the headset and a warning capsule on the receiver/display. As the aircraft closes in on the energized wire, both the volume and frequency of the tone increase, with a steady WARN light. Maximum range for the unit is about 3,000 feet, and varies with the intensity of the field. The stronger the field or closer the aircraft is to the field, the more intense the audio warning.
To experience the PDS in action, one recent morning B&CA strapped into Safe Flight’s Bell 206 and went hunting. We selected a nearby suburban area we knew was festooned with a variety of powerlines and headed out. Our primary interest was residential supply and wires less than 100 feet high, which are of most concern to pilots who fly in the wire zone.
Down to the Wire
For our first target, we selected a typical, three-phase set of 115 kV powerlines that crossed a river about 100 feet above the surface. Using a bridge that was about 4,000 feet away from the lines (verified by GPS) as a reference and flying at 1,000 feet and 100 knots, we set up a flight path perpendicular to the wires. Shortly after passing the bridge, the audio warning began to click in a moderate beat. Within 10 seconds the clicking frequency and tone increased noticeably and the visual indicator illuminated. As we closed to within 20 seconds of striking the lines, the frequency and volume of the warning became impossible to ignore, beckoning for evasive action.
We executed an evasive climb, but the warning did not begin to dissipate until we added about 500 feet in altitude. Repeating the procedure, and executing a 180-degree turn, reduction in tone did not begin until we had backtracked at least another 500 feet.
The system does not give cues for avoidance tactics, the most common of which is to climb. Obviously, that maneuver could prove disastrous if the aircraft is immediately below a wire.
Next, we flew an oblique intercept of the wire. The warnings repeated at the same closing distance.
Using a knob, we decreased system sensitivity approximately 25 percent and still got an unmistakable warning when we closed to within 1,000 feet of the lines.
Flying along at 2,000 feet over a populated area with multiple residential supply lines the PDS produced an occasional tone, which was neither alarming nor annoying. The mute switch can also be used when in cruise to silence such unwanted warnings. When it is selected, a “MUTE” light on the switch illuminates.
We scouted for an area to test the system on lower voltage residential lines, thereby simulating a departure from a field location. Using a small lake as a substitute for a landing field, we identified a residential powerline that followed a bridge across the narrow end of the lake. The powerline was about 20 feet above the water’s surface. We approached the line head-on and started receiving indications when about 1,000 feet distant and by 500 feet were receiving steady, unmistakable warnings. We repeated the exercise with the same result. The field simulation had been undeniably successful.
Affordable and Practical
Total cost for the Safe Flight wire warning system is about $12,500 for the equipment and a basic data package for local installation and approval. Installation time varies, but typical installation takes about two days. There are currently over 15 aircraft operating the system. Safe Flight holds several STCs for helicopters including the Bell 206 family and Aerospatiale Gazelle, with installations also available for the Eurocopter EC 135, AS355 and AS365, and the Mil-17. Interest in the system is very high among airframe OEMs. Since PDS is an aid and not a flight or communications instrument, it is not TSO certified, but the manufacturer says the system does meet RTCA DO-160D.
About 17 percent of wire strikes involve de-energized lines, the type that the Safe Flight PDS cannot detect. Even so, this shortcoming seems acceptable when viewed in the context of the overall problem; after all, live wires, which the PDS does see, account for 83 percent of the strikes. Thus, the Safe Flight system can help pilots avoid the far more common hazard.
Ironically, when an unlucky pilot does collide with wires, but is lucky enough to survive the encounter, his bad luck can return after extricating himself from the wreckage.
Power companies may sue for revenue lost during the interruption of power flow and for the cost of repairing the line. Since some high-capacity power lines provide $1 million worth of juice per hour, the post-strike tab could be hefty indeed. (It’s hardly surprising then that a survey performed by a major university suggests most wire strikes in which the aircraft is not destroyed go unreported.)
While the Safe Flight PDS is not an all encompassing wire detector – nor is it promoted as such – it helps tremendously in alerting pilots to a whole lot of potential trouble. Helicopter pilots performing landing site reconnaissance at night or in low visibility, EMS crews on approach or departure, news gatherers in the heat of action, and even pilots who earn their keep inspecting and repairing power lines can all benefit from the PDS.
Yes, high-tech wire detectors, enhanced vision systems, and terrain and obstacle databases all help to keep pilots clear of wire hazards. The Safe Flight PDS is one more tool in that lifesaving array, one that provides a simple, affordable solution for those who need it the most, and in some cases, can afford it the least. The PDS provides pilots with an extra set of ears to complement an already busy set of eyes, so they can hear the hum of the wires without feeling their sting. B&CA