EASA SIB CASA-2018-10
Bell (BHTC) 206L, 407 and 505 Helicopters - Cracking of Main Rotor Transmission Gear
Summary
The Transport Canada Civil Aviation Safety Alert CASA 2018-10 addresses the issue of cracking in main rotor transmission bevel gears on Bell Helicopter models 206L-series, 407, and 505. It highlights the occurrence of cracked gears primarily in model 407 transmissions and discusses the development of a welded gear assembly part number 407-040-043-101 to reduce cracking risk. The alert emphasizes compliance with operational and maintenance procedures related to chip detector activations to ensure safety.
What Changed
This new safety alert raises awareness of the potential for main rotor transmission bevel gear cracking and reinforces the importance of strict adherence to flight and maintenance manual procedures when chip detector activations occur. It introduces the recommendation for voluntary installation of a welded gear assembly on model 407 helicopters to mitigate cracking originating from bolt holes. The alert also clarifies the vulnerability of models 206L and 505 to this issue based on their transmission design.
Why It Matters
For aviation professionals, this alert is critical because cracked bevel gears can lead to transmission failures if not detected and managed properly. Operators and maintenance teams must ensure the transmission chip detector system is functional and respond correctly to activations to prevent unsafe conditions. Understanding the risk and following recommended procedures helps maintain airworthiness and avoid costly repairs or accidents.
What To Do
Operators should always keep the transmission chip detector system operational and strictly follow flight and maintenance manual instructions when chip detector activations occur. If multiple chip detector activations happen within a short time despite acceptable serviceability checks, the transmission should be removed and inspected per repair manual requirements. Model 407 operators are advised to consider installing the welded gear assembly P/N 407-040-043-101 during the next transmission overhaul or repair visit.