The thorny topic of wire strikes is highly debated in the domain of helicopter operations. In general, they are considered significant contributors to accidents and incidents. Over the years, several solutions have been developed to reduce the risk of wire strikes, including training protocols for pilots, advanced mapping systems with cable locations, as well as equipment that reduces their impact.
Some operators have software that interacts with the terrain awareness warning system (TAWS), or other onboard operations capable of indicating to the pilot the presence of mapped cables in the operational area – and defining them as obstacles. AirMed&Rescue spoke to a European air rescue pilot, who asked to remain anonymous. He said: “The mapping may not be ‘fail-safe’ by itself and it is preferable to trust it in a very restricted airspace. Many helicopter types can be equipped with ‘cable cutters’, which are often required in helicopter emergency medical services (HEMS) procurement. The system is certainly useful but is considered a last resort because, when deployed, the helicopter has already hit the wires, and its effectiveness depends on the direction of impact, size of the wire, helicopter speed and other factors.”
Many helicopter types can be equipped with ‘cable cutters’
The efficiency of cable cutters is designed to increase when the helicopter strikes the wires at angles of less than 90 degrees and speeds more than 30 knots (35mph), according to Michael Biasatti, a helicopter air ambulance (HAA) pilot in the US. “It cuts a 3⁄8-inch (9.5mm) steel cable with a breaking strength of 12,000lb (5,400kg). Typically, when operating at altitudes that would place the aircraft in the vicinity of wires – at least for HEMS/ HAA operations – the aircraft approaches and departs slower than 30 knots, which would likely have some effect on how well the wire strike protection unit could do its job,” he said. “Helicopters used for agricultural purposes operate at high airspeed and low altitude during spraying and seeding operations, with a much higher degree of exposure to the risk of wire strike events.”
Regarding night operations, the implementation of night vision goggles (NVG) has significantly enhanced the ability to locate and identify various hazards on approach, but even with these, wires are still hard to see. For night vision to be effective, there must be some ambient light for the goggles to magnify, said Biasatti. “Also, we observe the industry ‘sterile cockpit’ standard for all phases of flight other than cruise, so every crew member is focused 100 per cent on safely arriving and departing from the rescue scenes.”
Hospital helipads are usually well thought out in terms of providing a safe approach and departure path, but progress seems to slowly erode these clear areas as hospitals add new facilities, parking garages and the like, according to Biasatti. “Diligence and discipline in following procedures and operating within an acceptable level of risk while approaching and departing a landing area is paramount,” he said. “An upper and lower wire strike kit or cable cutter helps facilitate a safe outcome in the event that avoidance procedures prove unsuccessful. These are the last line of defence.”
Wires are very difficult, if not impossible, to see until it is usually too late
Concerning crew protocols, a thorough briefing takes place at the beginning of every shift, with safety always the first topic of discussion, affirmed Biasatti. “Plans and practices for landing in any number of remote locations are included in this shift change briefing. Speaking specifically to wire strike avoidance, we emphasize looking for towers in and around the proposed landing zone (LZ), as wires will be nearly impossible to see. But towers occupy a greater degree of one’s visual field and if approaches and departures are planned to fly over them, the aircraft should remain free of those hazards,” he said. “Wires are very difficult, if not impossible, to see until it is usually too late. Towers are obviously much easier for the eye to locate, then one should just apply the old aviation adage whereby all towers have wires.”
In mountain operations, helicopter pilots are taught from their very first navigations to enter a valley higher than its mountains. “However, this is often not possible, and pilots are taught to try and identify the presence of pylons through which to search for the wires. The cables are difficult to see in unfavorable light conditions, even at night with NVGs,” the air rescue helicopter pilot said. “On approaches to the ground, pilots are taught to conduct a reconnaissance at ever lower altitudes, continuously looking for the presence of pylons; seeing the wires before the pylons is a sign that the reconnaissance has not been done well, so the training task has not been performed correctly by the student.”
Any crew member who identifies a hazard can call for an abort, with no questions asked.
During normal operations, it is good practice to approach any area of intended landing from a position that allows a wide visual field to assess for risks, and then to conduct a high reconnaissance around that area to further examine any hazards, according to Biasatti. “Following all that, and with full crew agreement, we set up for an approach, conduct a low reconnaissance (confirming everything we identified during the high reconnaissance), then proceed onto our approach path,” he said. “Any crew member who identifies a hazard can call for an abort, with no questions asked. When this occurs, the approach is discontinued, climb power is added, and a climb out at Vx is initiated. Once established at a safe altitude and airspeed, we then discuss the hazard necessitating the abort call and determine an alternate landing area or course of action.”
A virtual platform
Biasatti observes that there are some off-airport operations conducted during training cycles that incorporate the risk of wire strikes into virtual reality (VR) training. “VR is a great platform to learn and reinforce proper procedures. The visuals are very good, but it is difficult to completely replicate the nearly infinite variations of visual appearance that wires will present to the human eye,” he said. “Wire strike incidents are 100 per cent avoidable, with proper training, risk management and crew resource management going a long way towards achieving the ultimate goal of safety.”
Wire strike incidents are 100 per cent avoidable
There is plenty of work to be done before VR can be fully deployed to help reduce the risk of wire strikes. “The wires must be avoided, and it is difficult to simulate what happens once the wires are hit, because it depends on too many factors,” the air rescue helicopter pilot said. “Helicopter companies that carry out specialized operations at low altitudes are trying to deepen understanding of the geographical area or employ pilots with a deep knowledge of the territory in which they operate. This is certainly a ‘soft’ barrier, but currently seems to be the most effective one.”