Main Rotor — Expandable Blade Bolt incorrect heat treatment
- Published
- Effective
- Replaces
- 2025-21
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Operators of Bell 407 and 427 helicopters must remove and replace all expandable blade bolts with part number 406-310-103-103 and serial numbers listed in the updated Table 1 within 30 hours air time or 30 days from December 1, 2025, whichever comes first. Installation of affected bolts is prohibited from the effective date. Compliance must follow the instructions in the respective Bell Textron Alert Service Bulletins approved by Transport Canada.
Summary
Canadian Airworthiness Directive CF-2025-21R1 addresses an issue with expandable blade bolts, part number 406-310-103-103, installed on Bell Textron Canada Limited model 407 and 427 helicopters. The directive identifies that some bolts may have incorrect heat treatment, which could lead to stress corrosion cracking and potential main rotor blade detachment. This directive mandates inspection and replacement of affected bolts to ensure continued airworthiness.
What changed
CF-2025-21R1 revises the original AD CF-2025-21 by correcting a serial number error in the list of affected expandable blade bolts. It maintains the original requirements for removal and replacement of the specified bolts but updates the serial number table to ensure accurate identification of affected parts.
Why it matters
This directive is critical for aviation professionals because incorrect heat treatment of main rotor blade bolts can cause structural failure leading to loss of helicopter control. Operators, maintenance organizations, and compliance teams must address this promptly to prevent in-flight failures and ensure regulatory compliance. The update clarifies affected parts, reducing the risk of oversight during inspections and replacements.
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