Superseded by CANADIAN AD CF-2020-15
- Published
- Effective
- Deadline
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Operators must replace the MS21042 nuts with NAS9926 nuts within 600 flight hours or 24 months from the effective date, whichever occurs first. After installation of NAS9926 nuts, MS21042 nuts are no longer permitted on the tail rotor drive shaft couplings. Maintenance organizations should acquire sufficient NAS9926 nuts inventory to support ongoing maintenance and comply with the Bell Helicopter service bulletins referenced in the directive.
Summary
Canadian Airworthiness Directive CF-2019-34 addresses the failure risk of bolted fittings in the tail rotor drive shaft couplings on Bell Helicopter Textron Canada Limited models 206, 206A, 206A-1, 206B, 206B-1, 206L, 206L-1, 206L-3, and 206L-4. The directive mandates replacing MS21042 series nuts with NAS9926 series nuts to prevent potential tail rotor drive loss. This AD aims to enhance flight safety by mitigating the risk of tail rotor control failure due to nut cracking or loss.
What changed
This new Canadian Airworthiness Directive requires the replacement of MS21042 series nuts on the tail rotor drive shaft couplings with NAS9926 series nuts, which are less susceptible to hydrogen embrittlement and failure. It prohibits reinstalling the original MS21042 nuts once the NAS9926 nuts are installed. The directive also references Bell Helicopter service bulletins 206-19-136 and 206L-19-181 as the approved procedures for compliance.
Why it matters
This directive is critical for operators and maintenance organizations to prevent tail rotor drive loss, which can lead to loss of helicopter control. Compliance ensures continued airworthiness and safety of affected Bell 206 series helicopters. It also impacts inventory management as NAS9926 nuts are newer and less commonly stocked, requiring proactive procurement by maintenance providers.
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- EASA AD US-2024-20-07Equipment / Furnishings - Emergency Float Kit Activation Handle - Repetitive Inspections / ReplacementNov 29, 2024
- EASA AD CF-2022-33Tail Rotor Drive — Failure of Tail Rotor Drive Shaft with Bonded AdaptersJun 22, 2022
- EASA AD US-2021-24-15Tail Rotor Drive - Oil Cooler Blower Shaft Drive Ring Spline Teeth and Mating Area Spline Teeth - InspectionDec 16, 2021
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