Wire strike protection

December 10, 2009 by Tim McAdams

I fly a Bell 206 JetRanger helicopter as a demonstration aircraft for my company’s autopilot and glass cockpit systems. It is equipped with a Wire Strike Protection System (WSPS) and many times I am asked what it is and how it works.

Bell 206 with Wire Strike Protection

Bell 206 with Wire Strike Protection

The system on the Bell 206 has three main components: an upper cutter, lower cutter, and deflectors. Each cutter has a deflector that forces the wire into sharp high-tensile steel blades (they are rubber coated to prevent inadvertent injury to service personnel). An additional deflector strip runs vertically between the pilot and copilot windscreens to guide the wire to the upper cutter. On different helicopters other deflectors are mounted as necessary to protect critical areas. For example, on the toes of the skids to force a wire to go under the helicopter and stop it from getting caught between the skid gear and the fuselage.

It is a passive protection system that reduces the chances of an accident in the event that the helicopter is flown into horizontally strung wires. The key phrase is “reduces the chances” as the system is not 100-percent effective. In order to work properly the helicopter needs forward speed; faster speeds increase the probability of cutting the wire. Also the level of effectiveness is a function of several other factors including where the wire impacts the fuselage, the cable tension, and the diameter of the wire.

The US Army evaluated the WSPS by performing pendulum swing tests using a Bell OH-58 (basically a military version of the Bell 206). The tests went well and they adopted the system for use on U.S. Army helicopters. Since then several Army helicopters have hit wires that were then cut by the system resulting in no injuries and minimal to no aircraft damage. Several civilian helicopters equipped with the WSPS have cut wires and avoided an accident as well.

Of course the best protection from wire strikes is prevention. Some things to consider are only flying below 500 agl when it’s necessary, looking for poles because they are easier to spot than wires and when you need to fly low over wires cross at the poles or supporting structures. Additionally, when landing in unapproved areas be sure to perform a complete aerial reconnaissance. If your helicopter is equipped with wire strike protection it should be viewed as a last line of defense.

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22 Responses to “Wire strike protection”

  1. Dale Long Says:

    Enjoyed your post, as usual. As an Army Flight Surgeon ’79-’83, I remember several wire-related fatalities before WSPS. Most memorable were those with Night Vision Goggles getting ready for the assault in Iran during the last year of Jimmy Carter’s presidency (starting in the Spring of 1980). That group trained exclusively at night, flying mostly NOE with night vision goggles. Of course, Army guys didn’t get to do that mission. The Marines got the green light as would be expected, and that hostage rescue attempt didn’t go well due to blowing sand, aircraft colliding, etc.

    Anyway, on one of those flights early on, a group flying in a close formation (NOE) near their home base, hit guy wires on a tower ( running obliquely to ground) that was anchoring a tall antennae. That incident, and others were quickly cleared up due to the secret nature of military training for night assault missions at that time. It isn’t likely one could pull that data up for review. However, the threat of hitting wires… flying in low places… at night… was happening ongoing and WSPS came on-board within months and the Army’s fleet of Hughes 500′s and the OH-58′s all got them fairly quickly. Blackhawks came out within a couple years after that. They had collapsable gear, pilot seats, WSPS and lots of other safety stuff to protect aircraft and pilots.

    Another incident I remember is related to a MAST (Military Assistance to Safety and Traffic) Huey flying a civilian mission to pick up blood products from one regional hospital and deliver to another hospital less than an hour away from the first. Cruising low along a highway under cloud cover, the aircraft struck wires that crossed the road. With loss of forward speed from wire catching the mast, and the chopper hit the ground hard in a vertical descent. Pilot was killed instantly, the co-pilot severely injured (might have died later, I don’t remember) and the paramedic in back had spine fractures, etc., but was awake throughout the incident and had a lot to say about the pilot (none of it was kind).

    For what it’s worth, I went on to add-on a commercial rotorcraft to my FAA fixed-wing ratings in 1981. Only recently did I get back to flying helicopters and very much enjoy your reports.

    Please keep writing.

  2. Chris Says:

    I saw video of the OH-58 swing tests last year at HAI. Without the kits, and with the fuselage swinging at a relatively low speed, even a small wire sheared the mast completely off.

    Given that wire strikes are one of the most common causes of helicopter accidents, operating in the wire environment is a sorely neglected topic in primary training.

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