The FAA on Friday issued emergency airworthiness directive 2023-17-51 that requires a one-time tail rotor blade tap inspection on all Bell 407 helicopters. The FAA took the action the day after Transport Canada issued a similar, but more limited, action that required the inspection of certain serial-numbered Bell 407s to detect debonding from skin core voids created by missing adhesive between the upper and lower skin core. The anomaly was discovered after an operator detected a strange sound while manually rotating a tail rotor blade.
Skin core voids that exceed allowable limits can cause severe vibration, failure of the tail rotor blade, and loss of tail rotor control. The actions taken by both agencies follow Bell Alert Service Bulletin (ASB) 407-23-132 issued on August 14, which identifies specific part numbers and procedures for inspecting the blades. Depending on inspection results, the Bell ASB requires the return of the defective blade to Bell for investigation and replacing the blade. The FAA is requiring the inspection to be completed within 10 hours time-in-service or 14 days, whichever comes first.
The FAA noted that “debonding of a [tail rotor (T/R)] blade could lead to instantaneous failure before detection. Additionally, affected T/R blades are installed on high-usage helicopters, which could increase the likeliness of occurrence of a failure.”