N76646Cessna 120

The pilot of the tail wheeled-equipped airplane reported that, he was on an approach to land at an uncontrolled airport behind two helicopters. An airport surveillance video showed the accident airplane flying over the runway about 20 seconds after a helicopter was in a slow hover taxi adjacent to the runway. The pilot reported that he saw the helicopter and decided to land long to maintain separation. He added that while on short final, he saw a helicopter “cross” the runway, so he increased engine power to full and attempted a go-around. About one-third of the way down the length of the runway, the airplane encountered the helicopter’s downwash, and the airplane entered an uncommanded steep right bank. The pilot applied opposite aileron, but he was not able to maintain control of the airplane. Subsequently, the airplane impacted right of the runway and sustained substantial damage to the right wing and fuselage. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.

According to Federal Aviation Administration Advisory Circular No. 90-23G, Aircraft Wake Turbulence, “pilots should avoid taxiing or flying within a distance of three rotor diameters of a helicopter hovering or in a slow hover taxi, as the downwash can contain high wind speeds.

Figure 1. Except of Helicopter Vortices Figure from AC 90-23G