Wire strikes are a seriousthreat to helicopter safe-ty. Ranked as a leading

cause of rotorcraft accidents world-wide, power lines claim on average2 helicopters every week. Any air-craft operating below 1000 ft is vul-nerable to a wire strike—and, sincemost helicopter missions involveprolonged flight at low altitudes,the risk is particularly high for thissegment.Government and industry safetyorganizations support a multilay-ered strategy to combat this threat.Mitigation strategies include train-

ing, awareness and technology,both airborne and on the ground.The threat of wire strike accidentsincreases daily. In the US alone, theweb of power lines covers 4.5 mil-lion miles and is growing. Industryand consumers around the worldhave an ever-increasing appetite forpower and connectivity. To satisfythis demand, utility companies arebuilding continually on vast net-works of wires, towers and newtechnologies such as wind turbines.Like a spider web, this growing net-work silently awaits its prey.FAA, NTSB and industry studies

identify wire strikes as a factor inroughly 5% of all rotorcraft acci-dents. For civilian aircraft, decadeto decade, this rate is highly consis-tent, although since 1996 theseaccidents are becoming moredeadly.For the rotorcraft industry, wirestrike accidents are very troubling—the threat is hard to see, the acci-dents are often fatal, and in everycase it either substantially damagesor destroys the aircraft.Utilities/Aviation Specialists PresRobert Feerst, an expert in wirestrike prevention, says, “At typical

84 PROFESSIONAL PILOT / November 2012

By Stuart LauATP/FE/CFII. Boeing 747/747-400,757/767, CRJ, Saab 340

HELO AIR SAFETY

A plan for reducing wire strike accidents

Powerline sensors, HTAWS and specialized trainingcan significantly lower helo collision rate with cables.

Most helicopter missions are flown at very low altitudes, and powerlines are often nearly invisi-ble to pilots. Specific training in the “wires environment,” proper crew resource managementand technology can all lessen the threat of an accident.

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flight speeds, wires are almost invis-ible. If there is one takeaway, wireand obstruction strike accidents arepreventable if the pilots and crewunderstand what the enemy lookslike. You have to have the awarenessevery time you operate in the wiresenvironment. Until you have a basicunderstanding of what can get youin trouble, it’s a lethal place.”Unlike other accident categories,experience and weather are not typ-ically identified as causal factors inwire strike accidents. In fact,according to FAA, the average ageof the accident pilot is 43.5 years,with over 4000 hrs of flight time.Likewise, the weather is typicallygood—86% of these accidentsoccur in daytime VMC.During the 1990s, lighter pistonand turbine-powered helicopterssuch as the Robinson R22/44 andBell 206 series accounted forapproximately 2/3 of all wire strikeaccidents. In recent years, larger,more advanced helicopters havebeen involved in an increasingnumber of deadly collisions withobstacles such as wires and towers.On Jun 30, 2012, a EurocopterAS350B was destroyed while flyingat low altitude in VMC through theVerde River canyon near CampVerde AZ. The accident occurredwhen the aircraft struck a cablespanning the river. Investigatorsfound a severed steel cable on theeastern shore of the river. Both thecable and aircraft main rotor bladeshad evidence of wire contact. Thesevered cable, which normallywould have been suspended 40–50ft above the river, had gray paintand composite blade fibers embed-ded in the wire strands. Two of the 3main rotor blades were damaged 3ft inboard of the tips. The pilot and3 passengers were killed.On Jul 25, 2012, a EurocopterAS532 Cougar—a Super Pumaderivative—on a predelivery testflight collided with electrical cablesin the mountainous Gorges duVerdon (Alpes-de-Haute-Provence).The daylight flight under VMC hadoriginated from Marseille and wascarrying 6 Eurocopter employees fora final verification flight prior todelivery to the Albanian Army. All 6Eurocopter employees died in theaccident.On Aug 5, 2012, a PHI Air Medic -al Bell 407 operating as an EMS

flight from College Station to SanAntonio TX collided with a cellphone tower. While operating underPart 135 in night-time VMC, the air-craft struck the tower, damaging alanding skid. The flight endeduneventfully due to some quickthinking by firefighters at SAT (Intl,San Antonio TX). On notificationfrom ATC, the firefighters construct-ed an impromptu “landing pad”with mattresses and weights fromtheir living quarters. The pilot, flightnurse, paramedic and patientescaped injury following a “bal-anced landing” with a severed skid.

Intervention recommendations

In 1980, NASA released CivilHelicopter Wire Strike AssessmentStudy—a report that analyzedNTSB and FAA accident reports.The study made several recommen-dations of interventions to mitigatethe threat, such as pilot warningdevices, wire cutters and improvedtraining. The authors concludedthat pilot warning devices wouldhave been beneficial in preventing76% of the accidents, wire cutterswould have been 49% effective,and pilot training would have madea difference in 56% of the cases.In Aug 2011, the Intl HelicopterSafety Team (IHST) released its ana -lysis team’s Compendium Report,

which analyzed 523 US civil heli-copter accidents from the calendaryears 2000, 2001 and 2006. IHST’sintervention recommendations mir-rored the earlier NASA study insuggesting improved pilot trainingand the installation of equipmentsuch as proximity detection sys-tems, wire detection systems and awire strike protection system (WSPSor wire cutters), any or all of whichwould help mitigate the threat of awire or object strike.In the context of a proactive safe-ty management system (SMS)—andbased on the severity (loss of equip-ment and harm to the occupants)and frequency of these accidents—operators would be required to putcontrols in place to mitigate the riskassociated with continued flightoperations at low altitudes. Themost successful risk mitigationstrategies involve employing bothsoft and hard safeguards (controls).Soft safeguards may include pro-cedures and training focused onpreventing collisions with obstaclessuch as wires and towers. A FlightSafety Foundation (FSF) study sug-gests a thorough preflight review ofaeronautical charts and high-alti-tude surveillance or reconnaissanceflights over the area of operations.While familiarity with all terrainand obstructions in an area is desir-able, this becomes challenging

PROFESSIONAL PILOT / November 2012 85

Safe Flight’s powerline detection system (left side of instrument panel) “listens” for the electro-magnetic signature of energized power distribution lines. As the helicopter nears the live wire,the audible tone increases in frequency, providing ample warning to the pilot to change the air-craft’s flightpath.

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when covering large geographicareas—and it is important to under-stand that not all power lines andtowers are charted. High-altitudereconnaissance flights will aid thepilot in locating towers and wires,but maintaining a high level of situ-ational awareness is difficult whileflying single-pilot during periodsinvolving multiple distractions—both internal and external—such asradio communications or searchingfor airborne traffic.

An invisible threat

According to an FSF report,experts agree that precautions suchas a chart review and reconnais-sance flights may not be adequatefor detecting all wires. MultipleNTSB accident reports supportclaims that wires are often nearlyinvisible in flight. Contributing fac-tors vary widely—from dirty wind-shields to low light, or even toomuch light when flying directlytoward the Sun.Optometrist Warren DeHaanadds, “Pilots notoriously have themis conception that they will see thewires in time at the wire level. Youjust cannot count on it. The wire isnot consistently visible.”Feerst adds, “Wires are difficult tosee, partly because the way thehuman eye functions and partlybecause of the effects of some back-grounds and light angles in camou-

flaging wires. The eye starts to loseits visual acuity at 3° off center.Unless you’re looking right at thewire, you’re unlikely to see it.”Having trained more than 25,000crewmembers worldwide since1985, Feerst adds, “There is no sub-stitute for training. Our courseteaches core survival skills for low-level operations—this includes crewresource management (CRM) for notonly the pilot, but all occupants ofthe aircraft, whether it’s a para -medic, lineman, observer or patrol-man.”

Feerst notes that, during single-pilot ops in the low-level wires envi-ronment, it is critical to have every-one engaged in the search for haz-ards. CRM is a core component ofhis wire strike prevention courses.HAI recommends formal training forany operator engaged in low-levelflight operations.Hard safeguards may include theuse of airborne technologies and/orground equipment to prevent orprovide an added level of protectionto the aircraft and its occupants dur-ing low-altitude flight ops. Airbornetechnological solutions may includeboth preventative systems and reac-tive devices.Preventative systems include prox-imity detection systems such as ter-rain awareness and warning systems(TAWS) and power line detectionsystems. Reactive devices includewire cutters. Ground-based equip-ment ranges from simple sphericalpower line markers to more techno-logically advanced obstacle colli-sion avoidance systems.Sandel Avionics HeliTAWS is aunique proximity detection systemthat combines WireWatch—a con-tinuously updated database ofknown power lines and towers—with a high-resolution terrain andobstacle database. Sandel CEOGerry Block says, “Just as HeliTAWSitself helps pilots avoid CFIT, ourWireWatch feature helps eliminatethe hazard of near-invisible trans-mission lines by enabling helicopter

86 PROFESSIONAL PILOT / November 2012

Wire strike protection system (WSPS)-equipped Bell 407 operates at low altitude. As a last line ofdefense, WSPS can lessen the consequences of a wire strike accident by slicing through the cable.

Safe Flight says its powerline detection system—a low-cost, lightweight detection system—can beinstalled in a helicopter in 2 days. More than 50 examples are in service on 17 helicopter types.

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crews to spot known wires.”Launched during Heli-Expo 2011,HeliTAWS is the only multihazardavoidance system currently avail-able. WireWatch provides pilotswith additional situational aware-ness and alerting of known wiresabove 100 ft AGL. The database isupdated using information from util-ity companies and operators.Several power line detection sys-tems have been developed in recentyears. Safe Flight Instrument Corp’spowerline detection system (PDS) isan example of a relatively low-costdevice designed to warn pilotswhen they near wires that are ener-gized. Safe Flight’s PDS senses theelectromagnetic field generated bylive electrical power lines and emitsa pulsing audible sound and visualalert. Alerts begin around 1800 ftand the frequency of the audiblesound increases as the helicopternears the wires. According to themanufacturer, only 17% of wirestrikes involve de-energized lines.Thus, PDS would have effectivelyprovided a warning in 83% of theaccidents. Currently, more than 50Safe Flight PDS systems are installedon 17 different helicopter typesworldwide. Installation of thereceiver, display and antenna takesapproximately 2 days. Cost is rough-ly $12,500.Helicopter laser radar (Hellas) isanother more advanced and costlydetection system that uses an eye-safe laser to scan the environmentfor wires and other flight obstacles.Developed by Fairchild Controls—an EADS company—the system pro-vides optical and acoustic signals towarn pilots of a hazard. Hellas isdeployed on several advanced heli-copters and costs in excess of$100,000.A WSPS or wire cutters may lessenthe consequences of a frontalimpact with power lines. A typicalinstallation consists of a roof-mount-ed cutter and one or more other cut-ters on the airframe. The system alsoincorporates a deflector that runsvertically along the windshield.For a WSPS to be effective, thehelicopter must be flying at speedsgreater than 30 kts and strike at anangle less than 60° to the wire (and± 5° of pitch). The system is design -ed to cut a 3/8-in steel cable with abreaking strength of 12,000 lbs. In1992, the US Army began equip-

ping all of its helicopters withWSPS. This, coupled with increasedwire strike awareness and preven-tion training, has greatly reducedthe number of fatal wire strike acci-dents. Worldwide, more than20,000 WSPS kits have been instal -led on 65 different helicopter types.Wire or aerial markers are coloredspherical balls (usually orange oranother high-visibility color)installed on the power lines by utili-ty companies. P&R Tech has beensupplying SpanGuard markers since1960. They are available in differentsizes and colors—some are equip -ped with reflective tape or paintedto illuminate at night.A higher-tech, ground-based solu-tion is the obstacle collision avoid-ance system (OCAS). Developed inNorway, its main feature is a power-ful low-energy radar that detects air-borne traffic approaching within 3miles of a power line or wind tur-bine. The radar tracks the aircraft’sheading, altitude and airspeed, anddetermines if a warning should beactivated. If it does so, all primaryground-based lights are activated,illuminating the threat to the incom-ing aircraft. An optional secondaryVHF warning can issue an audioalarm to the approaching aircraft.

Once the aircraft passes the sitesafely, all lights and alarms aredeactivated. Several utility compa-nies in Europe and Canada havedeployed OCAS.Wires continue to present a signif-icant risk in the low-altitude envi-ronment. While new wire strike pre-vention technologies hold promiseto reduce the number of accidents,not all aircraft are equipped and notall wires are marked. Feerst of Util -ities/Aviation Specialists agrees.“Tech nology is a wonderful thing,”he says, “but it’s a failsafe that’s nosubstitute for training.”The best methods for reducing thewire strike threat are educationabout this potentially lethal environ-ment and increased vigilance in thecockpit.

PROFESSIONAL PILOT / November 2012 87

Stuart Lau is a consul-tant. He leads theIHST HFDM WorkingGroup and acts as anIHST liaison to theGlobal HFDMSteering Group. He isalso a pilot for a largeinternational airline

and a safety and accident investigationcommittee member. Lau has been asso-ciated with Pro Pilot since 1996.

Sandel Avionics HeliTAWS is the industry’s only multihazard avoidance system. HeliTAWS pro-vides advance warning of terrain, obstacles and wires while virtually eliminating nuisancewarnings through its proprietary algorithms.

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