N411HUSchweizer 269D · 2003

On July 14, 2018, about 1115 eastern daylight time, a Schweizer 269D Configuration A, N411HU, was substantially damaged when it was involved in an accident near Stewartstown, Pennsylvania. The pilot and passenger sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated that he was flying toward the eastern side of Shoestring Aviation Airfield (0P2), Stewartstown, Pennsylvania, to begin a normal approach to runway 24, with wind from about 230° at about 8 to 10 knots. He reported that the landing approach was uneventful until he attempted to slow the helicopter. While the helicopter was at an airspeed of between 10 to 20 knots about 15 to 20 ft above ground level, he began to apply left antitorque pedal to start to hover. He stated that the helicopter then started turning clockwise; he instinctively applied left antitorque pedal, which did not stop the rotation. He added that he did not recall lowering collective or reducing throttle. The turning accelerated rapidly until the helicopter was spinning in 360° circles. After six to eight complete rotations, the spinning decreased but then accelerated again, with another five to seven turns clockwise until the helicopter impacted the ground. He stated that he did not recall hearing any audible alarms or any change in engine sound.

The passenger reported the helicopter began spinning clockwise and then impacted the ground, with the helicopter on its left side.

A witness who was located about 750 ft southeast of where the helicopter came to rest reported seeing the helicopter smoothly come to a hover at the end of the runway, remain stationary for more than 5 seconds, then cleanly rotate left while remaining in the hover position. He reported that the rotation did not slow/stop as expected after 90°. Instead, the left rotation continued an estimated six to seven turns while the helicopter maintained altitude and position. He reported that the turns stopped for about 1 second, then began again, with the helicopter drifting backward to the east and losing altitude. He reported that he did not discern the direction of the second set of turns but that a review of video taken by a nearby individual noted the second set of turns was to the right. He reported that the entire time he saw the helicopter, the engine sound was constant with no variation.

Postaccident examination of the helicopter revealed substantial damage to the main and tail rotor blades as well as the left fuselage and horizontal stabilizer. Antitorque control continuity was confirmed from the controls at each seat to the tail rotor. The tail rotor gearbox was firmly attached to its tailboom mounting frame, and the tail rotor gearbox and tail rotor swashplate operated smoothly when rotated by hand. There was no damage noted to the tail rotor pitch change mechanism. The tail rotor blades were manipulated by hand, and the control linkages and mechanisms responded appropriately with no binding noted. The transmission rotated smoothly with corresponding rotation of the main rotor head and tail rotor gearbox. The tail rotor control system was tested by holding the tail rotor blades while the left and right antitorque pedals were manipulated by hand through their full range of motion against their respective stops; no binding was noted, with changes in pitch in the tail rotor blades consistent with the antitorque pedal movements. A tension check of the tail rotor control cables revealed a reading between 58 and 59 lbs (the helicopter’s maintenance manual specified 60 to 65 lbs).

According to a helicopter manufacturer representative, the variation in required to actual measured cable tension would not have an effect on the tail rotor control system's capability to provide adequate control of the helicopter.

The wind conditions reported at York Airport, York, Pennsylvania, which was located about 13 nautical miles northwest of the accident, were from 230° at 8 knots.

Review of the Pilot's Flight Manual for the helicopter make and model revealed the main rotor diameter was about 28 ft. According to Federal Aviation Administration Advisory Circular (AC) 90-95, “Unanticipated Right Yaw in Helicopters,” loss of tail rotor effectiveness (LTE) is a critical, low-speed aerodynamic flight characteristic that could result in an uncommanded rapid yaw rate that does not subside of its own accord and, if not corrected, could result in the loss of helicopter control. The AC also states, "LTE is not related to a maintenance malfunction and may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots."