cpt
Unfortunately none of Stormscope, monitoring cloud vertical development or static on HF/ADF will guarantee not being struck in the N Sea. In the tropics etc, they will but the type of lightning is different there - mostly cloud to ground and the only time the aircraft gets struck is if it happens to be in the wrong place at the wrong time and a strike passes through it - because the strike originates (ie the zero C level is) a long way above normal heli operating altitudes.
In the N Sea since we have to operate around zero C in winter, the helicopter can act as the trigger for the first strike. So the Stormscope etc only tells you that you have just been struck.
The mechanism is that mixed phase hydrometeors are present around zero C (well I had to get that in somewhere!) ie its where the lighter ice and heavier liquid water are present. The lighter ice goes up in the updraft, the heavier water goes down and the friction between the two generates the static which builds up to form a strong electric field which can ultimately break down to give a strike. The maximum electric field strengh is at the zero C level. If a heli passes through that generating ionised air (from the rotor blades and turbine exhaust) the ionised air acts like the heli is trailing a conductor and triggers the discharge.
All this is confirmed by the fact that virtually all strikes on N Sea helis have been during the winter half of the year, despite the fact that lighting is more prevelant in the summer.
Each strike is potentially disasterous as even though the helis are certified to withstand a certain strike energy level, Nature does not live in JAR/FAR29-land or if it does, does not bother read the specs and may decide to exceed the certification energy levels.
Though most are not disasterous, they are very expensive with transmission trains, heads, blades etc normally needing replacement. If there was a way to avoid getting struck, we would be using it!
HC
(who once got struck whilst flying though thin stratus, with no vertical development, only speckled green on the radar, no turbulence, lighting not forecast or present anywhere else in N Sea that day etc etc (but it was around zero!))