Technicians reported missing cotter pins allowed a bolt to back out and damage the skin in the tail rotor area of a Bell 206 helicopter. The aircraft was removed from service to make repairs.
Synopsis
Technicians reported missing cotter pins allowed a bolt to back out and damage the skin in the tail rotor area of a Bell 206 helicopter. The aircraft was removed from service to make repairs.
Narrative
On Date during a scheduled 300 hour inspection the #5 tail rotor drive shaft hanger bearing mounting hardware was removed to facilitate pulling the tail rotor gearbox input flange to inspect and lubricate the splines. During the reinstallation the mounting hardware was installed and torqued but cotter pin was not installed. I was responsible for inspecting the reinstallation of the #5 tail drive shaft and failed to notice that the cotter pins were not installed in the mounting hardware.On Date1 on the same aircraft approximately 57 flight hours later; performing a 100 hour airframe inspection; we had the tail drive shaft cover off shaft for inspection of the hanger bearings. During the inspection we put hands on the bearings to look for wear and play of the mounting hardware. During this inspection the mounting hardware was still installed and secured. I again failed to notice the missing cotter pins.On Date2 during unscheduled maintenance approximately 55 flight hours after the 100 hour inspection; the aircraft was taken out of service for replacing hanger bearing hardware on forward sections of the tail drive shaft; upon reaching the #5 drive shaft hanger bearing; we discovered right hand mounting bolt had slipped out of its hole. This allowed the drive shaft to pivot on the remaining hardware resulting in the Thomas Coupling scratching the tail boom resulting in a replacement.Possible factors that contributed to the event were human factors. There was a lot of maintenance happening during the 300 hour inspection. I cannot recall why this happened on the day we were reinstalling the hardware. I don't know if I was distracted that day or stressed that caused me to miss that part when inspecting. Learning from my mistake and looking thoroughly to all components that are affected during maintenance to make sure this doesn't happen again would be the best corrective action.
Second reporter narrative
On Date during a Scheduled 300 Hour Inspection the #5 tail rotor hanger bearing and short shaft was removed the facilitate inspection and lubrication of the tail rotor gearbox spline adapter. Upon Installation of the shaft the mounting hardware for the #5 hanger bearing was installed and torqued to 30-40 inch pounds however I failed to install the cotter pins. On Date1; approximately 57 flight Hours later we performed a scheduled 100 Hour Inspection which included checking condition and security of the hanger bearings and brackets at this time I deemed that all were secure and airworthy. I still did not notice that the cotter pins were missing from the #5 Hanger bracket hardware. I did however determine that the #2 & #4 bushes were starting to wear and decided to order parts and change them at a later date.On Date2; 55 flight Hours later I took the aircraft out of service to perform unscheduled maintenance to include replacing the bushes in the #2 & #4 hanger bearing brackets; it was at this time that I discovered the nut had come off of the screw on the right hand side of the #5 hanger bearing and the bolt had come out allowing the Thomas Coupling to contact the tail boom upper skin damaging both the Thomas Coupling and the tail boom. How this problem arose is a good question I don't really have an answer for that I made a mistake; I would normally have all the tool and pins with me to tighten and safety hardware I was obviously distracted but don't recall what the distraction was. I think we have enough checks and balances in place already and learning from my mistake will be the best prevention as far as this happening again goes.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.