What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The tail rotor transmission driven spline retaining nut lost its torque and backed out, causing the tail rotor drive shaft to move forward until the forward tail rotor drive shaft retaining nut contacted the upper aft bearing of the drive pulley "h"-frame. Normal clearance between the drive shaft forward retaining nut and the bearing is a minimum of 0.100 inches. This contact caused failure of the bearing grease seal allowing the lubricant to be lost. The overheated bearing caused overheating and fracture of the drive pulley "h"-frame. The forward pressure subjected to the tail rotor drive shaft was sufficient to bend the shaft and allow it to contact the right tail boom support attach bolt cutting a groove in the tail rotor drive shaft. The resulting vibration caused the pilot to make an emergency off-airport landing. Tail rotor control authority was maintained thoughout the landing. The drive pulley aft upper bearing had been installed new 404 hours prior. The tail rotor transmission driven spline retaining nut had been checked for proper torque 236 hours prior. The driven spline retaining nut has no safety mechanism other than torque and a plastic insert in the threaded area of the nut.
As the FAA filed it
THE TAIL ROTOR TRANSMISSION DRIVEN SPLINE RETAINING NUT LOST ITS TORQUE AND BACKED OUT, CAUSING THE TAIL ROTOR DRIVE SHAFT TO MOVE FORWARD UNTIL THE FORWARD TAIL ROTOR DRIVE SHAFT RETAINING NUT CONTACTED THE UPPER AFT BEARING OF THE DRIVE PULLEY "H"-FRAME. NORMAL CLEARANCE BETWEEN THE DRIVE SHAFT FORWARD RETAINING NUT AND THE BEARING IS A MINIMUM OF 0.100 INCHES. THIS CONTACT CAUSED FAILURE OF THE BEARING GREASE SEAL ALLOWING THE LUBRICANT TO BE LOST. THE OVERHEATED BEARING CAUSED OVERHEATING AND FRACTURE OF THE DRIVE PULLEY "H"-FRAME. THE FORWARD PRESSURE SUBJECTED TO THE TAIL ROTOR DRIVE SHAFT WAS SUFFICIENT TO BEND THE SHAFT AND ALLOW IT TO CONTACT THE RIGHT TAIL BOOM SUPPORT ATTACH BOLT CUTTING A GROOVE IN THE TAIL ROTOR DRIVE SHAFT. THE RESULTING VIBRATION CAUSED THE PILOT TO MAKE AN EMERGENCY OFF-AIRPORT LANDING. TAIL ROTOR CONTROL AUTHORITY WAS MAINTAINED THOUGHOUT THE LANDING. THE DRIVE PULLEY AFT UPPER BEARING HAD BEEN INSTALLED NEW 404 HOURS PRIOR. THE TAIL ROTOR TRANSMISSION DRIVEN SPLINE RETAINING NUT HAD BEEN CHECKED FOR PROPER TORQUE 236 HOURS PRIOR. THE DRIVEN SPLINE RETAINING NUT HAS NO SAFETY MECHANISM OTHER THAN TORQUE AND A PLASTIC INSERT IN THE THREADED AREA OF THE NUT.
Other reports on N958CP · 2
Matched to the same aircraft by N-number and date.