Helicopter wake turbulence
Forward flight: trails a pair of vortices like a large fixed-wing's wing-tip vortices. Low speed concentrates the wake, so it can be exceptionally strong. Heavier helicopter, stronger wake.
Avoidance: wake can spread over a large area. Adjust trajectory when operating or crossing behind a helicopter (TC AIM AIR 2.9).
Trap: assuming wake is weak because the helicopter is slow. Low speed concentrates it.
References
- TC AIM AIR 2.9
- FAA PHAK ch.5
- TC AIM RAC 4.1.1