Tuesday, December 1, 2009
Safety Watch: High Wire Act
While wire strike hazards to civilian helicopter operations are usually not found at the absolute top of most commonly recognized threat lists, this category of danger to flight is a consistent runner-up wherever mishap causes are identified in the rotary wing world. And nothing, pure statistics notwithstanding, can ever beat a wire strike threat for causing the helicopter operator’s blood to run cold. The most negative aspect of the wire strike hazard to helicopters is, in fact, that occurrences are often brutally catastrophic. The upside, though, is that bona fide wire strikes, and even near misses, are largely avoidable.
The first type of wire strike can be identified as “cruise-leg” encountered, and is in some ways the most perplexing to consider. A relative minority of enroute wire strikes occurs when helicopters are assigned to cover distances at very low altitudes for some specific operational reason.
The definitive example here would be an actual power line patrol, and most such operations involve pilots and crews very attuned and accustomed to flying safely in wire environments. But it turns out that other categories of enroute wire problems are somewhat self-inflicted, as more casual pilots engaged in simply transiting from A to B, possibly as a function of attempting to “entertain” passengers, or perhaps out of idle boredom, choose unnecessarily risky altitudes for “sightseeing” purposes.
Reading through accident reviews of this type of mishap can be exasperating, as scenarios in which perfectly good aircraft, often in good weather, are flown in close proximity to obviously existing terrain features, or through river valleys, where it is overwhelmingly likely, sooner or later, that wires will be encountered. Helicopters, within broad contexts, are safest when flown at moderately high altitudes, whether in wire environments or not. Both single and multi-engine helicopters give their pilots maximum opportunity for dealing with systems and operational surprises, right up to and including total power loss, when multiple hundreds or even thousands of feet, and consequently generous allotments of time, are available as a buffer between the onset of potential problems and encounters with terra firma. But when wirey complications are superimposed over a given operating area, the argument for staying conservatively high becomes even more incontestable.
Current charts that depict wires can be helpful in this instance, but alertness in visual scanning and common sense altitude discipline can be even better. The ultimate neutralizer for enroute wire strike threats is to stay intelligently high during transit phases, where flexible time and range opportunities for pilot actions can exist, and where wires cannot.
A second type of wire strike circumstance, legitimately more problematic, sets up as helicopters operate within their own unique brand of terminal operations, taking off and landing into and out of confined areas. In the developed western world, above ground wires are ubiquitous, and confined helicopter landing areas are very often defined by obstruction features predominantly created by wires. The EMS variety of civilian helicopter activities, of course, is particularly subject to this environmental reality. Necessary flight into known wire environments can be negotiated in ways that minimize the threat even at night, and many true wire-flying experts have accumulated many thousands of hours of safe operation in this unforgiving setting. Good reconnaissance techniques and the ability to avoid being rushed by mission urgency are probably the best tools here, but adequate lighting and night vision equipment can be very important as well. The use of closely controlled descent profiles is also effective, along with refined crew coordination practices, serving to multiply visual scan effectiveness.
Departure techniques are also critically important, since the wire strike threat can be at its most menacing during this phase. Even single-engine operators should fundamentally mimic Category II profiles, since the chances of an engine failure are dwarfed over time by the wire strike threat out of improvised landing zones. Within this context, disciplined control of aircraft weight and strict avoidance of any tendency whatsoever toward running takeoff profiles, which exponentially increase the likelihood of a wire strike, are absolutely critical.
Several classifications of miscellaneous equipment aimed at a variety of wire strike avoidance strategies are perpetually marketed, to include high visibility markers for wires themselves, along with actual airframe-mounted wire strike “cutter” equipment. In my programs we sometimes have the flight crews “preflight inspect” the cutting edges of this gear, checking for signs of “fresh use” in order to bring home the importance, by design, of arranging to never actually use some of our accessories.
Similarly, wire markers can be a good last ditch strike prevention tool, but the smart operator should never put himself in the position of depending on them in lieu of more fundamental safety protocols, undertaken much earlier in mission chronologies.
Those of us fortunate enough to live closely with helicopters know that they are truly magic, but those who have known this fascination for extended periods also know that the magic can never make wires disappear. They must be kept at a safe distance, by competent operators intelligently dedicated to doing exactly that.