MINDEN, NV, USA
N7183Y
Robinson R22 MARINER II
While hover-taxiing, the pilot experienced a sudden uncommanded right yaw. The aircraft was at a 5-foot hover when it spun 360 degrees (about the mast) to the right. The pilot attempted to stop the turn with full left pedal but the aircraft did not respond. After a full rotation, the lower horizontal stabilizer struck the ground. The aircraft had continued to spin an additional 180 degrees when the pilot rolled off the throttle, applied full up collective, and pressed the right pedal. The aircraft touched down abruptly next to the taxiway. The outboard 11 inches of one tail rotor blade had separated along with the outboard 6 inches from the second blade. Both separated blade sections were recovered with both showing similar leading edge damage near the blade tips. The geometric design of the vertical and horizontal stabilizer acts as a "stinger" or guard for the tail rotor. While there is evidence of ground contact with the lower horizontal stabilizer, it is indicative of lateral contact consistent with damage incurred during a right yaw. The damage to the vertical stabilizer shows evidence of mechanical loading originating from the movement of the lower horizontal stabilizer. The resultant loading produced left to right buckling of the vertical stabilizer just below the tail boom. This damage was also consistent with a right yaw. There was no evidence of contact between the either stabilizer and the tail rotor. The extent of damage to the stabilizers and geometric position of the tail rotor did not support the witness contention of contact between the tail rotor and the ground. The differential loading created by the unequal tail rotor blade separation resulted in an unbalanced system feeding back to the tail rotor gearbox.
On December 5, 1999, at 1400 hours Pacific standard time the pilot of a Robinson R22 Mariner II, N7183Y, lost tail rotor authority and made a hard landing at Minden, Nevada. The aircraft sustained substantial damage; however, the pilot and his passenger were not injured. The aircraft was being operated as a personal flight by the pilot/owner under the provisions of 14 CFR Part 91 when the accident occurred. The flight originated in Susanville, California, at 1200 earlier that day. Visual meteorological conditions prevailed at the time and no flight plan was filed. The pilot reported that he had completed a shallow approach to taxiway 34 at the Minden-Tahoe airport. After landing, he proceeded to hover-taxi toward the ramp over the taxiway. While hovering in, he encountered a fixed wing aircraft taxiing in the opposite direction. He cleared the taxiway by hovering toward midfield until after the aircraft had passed. He then rejoined the taxiway, about 100 yards behind the other aircraft. After hovering another 100 to 200 feet, he experienced a sudden uncommanded right yaw. He attempted to stop the turn with full left pedal but the aircraft did not respond. After the aircraft had completed between one to two 360-degree rotations, he rolled off the throttle, applied full up collective, and pressed the right pedal. The aircraft touched down abruptly next to the taxiway. It bounced left and right before finally coming to rest. The onboard passenger reported hearing a "loud noise" coming from the aircraft. A witness reported that the aircraft was at a 5-foot hover when it violently spun 360 degrees to the right. After the first full rotation, the tail rotor struck the ground. The aircraft continued to spin an additional 180 degrees before coming to rest. A post flight inspection revealed damage to both main rotor blades, both tail rotor blades, the tail rotor gearbox, and the vertical and horizontal stabilizers. In addition, the supporting frame beneath the left rear section of the engine compartment was buckled. The bottom sides of both main rotor tips were scraped, buckled, and bent upward. The outboard 11 inches of one tail rotor blade had separated, along with the outboard 6 inches from the second blade. Both separated blade sections were recovered with both blade tips showing similar leading edge damage. There was evidence of lateral bending on the lower section of the vertical stabilizer. The left side of the lower horizontal stabilizer was scraped. The tail rotor gearbox was fractured. A metallurgical examination found the fracture surface was consistent with an overload failure. The pilot had completed a biennial flight review (BFR) in the accident aircraft on the day prior to the accident.
the result of a foreign object contacting the tail rotor blade(s) while the aircraft was hover taxiing, which caused blade separation with subsequent loss of anti-torque (lateral) control.
Source: NTSB Aviation Accident Database
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