Most pilots are aware of the danger of wingtip vortices from heavy fixed-wing aircraft. And they understand the wisdom of avoiding the mini-tornadoes that flow invisibly outward and down. And intuitively, we all can easily imagine that a helicopter's rotor wash stirs up the air in the immediate vicinity — picture a turbine-powered ceiling fan. But how close is too close, when it comes to takeoffs, landings and taxiing nearby a helicopter? The Aeronautical Information Manual (AIM) has some guidelines. Section 7-3-7 reads: "Pilots of small aircraft should avoid operating within three rotor diameters of any helicopter in a slow hover taxi or stationary hover." For reference, that translates to giving a Bell 407 at least 105 feet of clearance (35-foot rotor diameter); and a Sikorsky S76 at least 132 feet (44-foot rotor diameter). Think about half a football field (150 feet) and you should have plenty of buffer. In addition, the AIM recommends caution when operating in the vicinity of a landing or departing helicopter, and by extension, even getting uncomfortably close at altitude: "In forward flight, departing or landing helicopters produce a pair of strong, high-speed trailing vortices similar to wing tip vortices of larger fixed-wing aircraft. Pilots of small aircraft should use caution when operating behind or crossing behind landing and departing helicopters."