Back in the CF5 Freedom Fighter days, static build-up on the duel wind screen was an every day occurrence. The solution to eliminate the problem was for a technician to discharge the electro-static build-up by wiping the screen. To do this, the technician used a 12 inch by 12 inch black rubber mat attached to a wooden broom pole and connected to the nose landing gear via a grounding wire with alligator clips. All too often, while moving around the aircraft, the alligator clip from the landing gear would come undone and a poor unknowing technician, trying to be of assistance, attempted to reconnect the clip to the nose gear. The end result was a technician doing the funky chicken (a solo twisting dance in the prone position). Electro-static discharge hazards are still around today but are most evident in helicopter fleets. Procedures to safeguard against the hazard are generally sound but improvements are warranted given the recurring occurrences involving electro-static discharges.
The CH124 Sea King community have set Standard Operation Procedures (SOPs) to deal with electro-static discharge hazards associated with its haul down and hoist systems. There have been occurrences where grounding was not carried out as per SOPs and this resulted in technicians and/or aircrew experiencing moderate to severe electro-static discharge, either while deployed at sea or ashore at their home base. One particular East coast occurrence comes to mind when a CH124 had an unsafe landing gear indication and two technicians attempted to install a landing gear safety pin while the aircraft was in the hover. During the process, the technicians received several electro-static discharges before finally getting the safety pin installed. All this happened because the aircraft was not grounded prior to the pin being installed.
The strength of a shock depends on both the current and the voltage. The lower the current, the greater the voltage can be without the shock causing harm and vice versa. The amount of energy released in a shock is measured in joules. At energy levels of five millijoules, the human body feels a shock; this is the threshold of sensitivity. At ten millijoules, the shock becomes uncomfortable. An example of this is the charge discharged when a person walks on carpet and then reaches for the grounded light switch. A 100 millijoule shock is severe and a one joule shock kills. To put this in an aviation perspective, a CH-54A “SkyCrane” helicopter recorded upward of three joules of stored energy and was thus capable of creating a lethal shock. Stored energy is not harmful yet it is the method of dissipation that can result in injury. The occupants of this CH-54A helicopter would also have had the equivalent of three joules of stored energy and would normally be protected by the airframe upon landing. This story changes if one of these occupants were to be hoisted down and become the direct link to grounding the aircraft.
Statistics show that there are still electro-static discharge occurrences for our helicopter fleets. The causes are varied. In a particular case involving the CH149 Cormorant, it was found that the static discharge cable (SDC) was not effective in reducing the aircraft potential. The SDC is a long cable used when hoisting to prevent or lessen any discharge to a person. It acts like a grounding cable, so when it makes ground contact, the helicopter potential is reduced with respect to ground. In this case, the SDC was not effective as no grounding was achieved due to the depth of snow. For another electro-static discharge occurrence, the SDC was simply not used due to snagging hazards in trees or boats and could not reduce the aircraft potential. Thus personnel on the ground should always regard a helicopter as a possible source of electric shock.
To raise visibility on this issue, a Hazard Report (Hazrep) is in effect to identify the electro-static discharge hazard for the CH149 Cormorant and to better understand the conditions under which static shock occurs. The Technical Authority is currently reviewing the possible application of static dissipative paint to the main and tail rotor blades and the possible replacement of the discharge cable snap hook on the hoisting system.
Technicians and aircrew members operating or interacting with hoist and haul down systems must be sure to check the equipment (“Deadman`s Stick”, static discharge wand, etc.) to ensure its availability and serviceability or the next act could be your solo funky chicken. Electro-static build-up should always be considered a real threat rather than a mere inconvenience as it can cause severe muscular spasms, local burns, and even be lethal. SHOCK and OW can be avoided!
