Main Rotor Drive — Engine-to-Transmission Drive Shaft Line Nuts — Inspection / Replacement
- Published
- Effective
- Deadline
- Replaces
- 2014-0118-E
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Operators of Bell 212, 412, and 412EP helicopters must inspect the affected nuts within 10 flight hours after 15 May 2014 and then every 25 flight hours thereafter. Any cracked nuts must be replaced before the next flight, and all affected nuts must be replaced within three months after 15 May 2014 if not previously done. Installation of affected nuts is prohibited from 15 May 2014 onward. Compliance can be achieved by following the instructions in the referenced service bulletins.
Summary
EASA Airworthiness Directive 2014-0118R1 is a regulatory document addressing the inspection and replacement of engine-to-transmission drive shaft line nuts on Bell Helicopter Textron Inc. 212, 412, and 412EP helicopter models. The directive focuses on nuts with part numbers MS21042L4 and MS21042L5, which were found to be susceptible to cracking due to a production defect causing hydrogen embrittlement. This AD mandates inspections and replacement procedures to prevent potential loss of main rotor power.
What changed
This revision of EASA AD 2014-0118 incorporates references to the applicable Bell Helicopter Textron Alert Service Bulletins 212-14-151 Rev. A and 412-14-160 Rev. A, which provide updated instructions for replacing affected nuts with serviceable parts. It supersedes the original AD issued in May 2014 and expands compliance guidance to include these service bulletins as acceptable methods for compliance.
Why it matters
This directive is critical for aviation professionals because undetected cracks in the specified nuts can lead to engine disconnection from the transmission, resulting in complete loss of power to the main rotor and compromised helicopter control. Operators and maintenance teams must ensure timely inspections and replacements to maintain airworthiness and safety. Compliance with this AD prevents potentially catastrophic failures and aligns with regulatory continuing airworthiness requirements.
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