EASA AD CF-2024-42: Main Rotor Drive System — Cracking of Transmission Oil Check Valve

What to do

Operators of Bell model 427 helicopters must measure the outside diameter of the transmission oil check valve housing within 25 flight hours or 30 days from 27 December 2024. If measurements indicate potential cracking, they must perform repetitive inspections every 25 flight hours or 30 days and replace the valve within 600 flight hours or 12 months. Installation of affected parts is prohibited from the effective date.

Summary

Canadian Airworthiness Directive CF-2024-42 addresses cracking issues in the transmission oil check valve part number 209-062-520-001 used on Bell Textron Canada Limited model 427 helicopters, serial numbers 56001 through 56084, 58001, and 58002. The directive mandates inspections, measurements, and eventual replacement of affected check valves to prevent transmission failure. It also prohibits installation of affected parts on these helicopters.

What changed

This new Airworthiness Directive introduces mandatory initial measurements of the transmission oil check valve housing, repetitive inspections for cracks and leaks, and replacement of affected valves within specified time limits. It also bans installation of affected check valves on Bell model 427 helicopters. The directive incorporates Bell Alert Service Bulletin 427-21-44 Revision A as the required compliance method.

Why it matters

This directive is critical for aviation professionals to prevent potential transmission failure caused by cracked transmission oil check valves, which could lead to loss of helicopter control. Operators and maintenance teams must ensure timely inspections and replacements to maintain airworthiness and comply with Canadian Aviation Regulations. Compliance reduces safety risks and avoids regulatory penalties.

What to do

Summary

What changed

Why it matters

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