Helicopter-triggered lightning strike

Helicopter-triggered lightning strikes is when a "helicopter itself [... is a main reason for a] lightning strike [... or hit. Other reasons] are needed to create the right conditions for helicopter"-"triggered lightning, which has been observed in [... the] North Sea [... and] sea near Japan".
These lightning strikes happen especially when there is snow fall and the temperature is around 0 degrees celsius.
The phenomenon has been studied for several years (as of 2015).