EASA AD 2021-0009R1
Air - Modulated Air System Control Valves - Lock-Out / Deactivation
Summary
EASA Airworthiness Directive 2021-0009R1 addresses the deactivation and lock-out of Modulated Air System (MAS) control valves on Rolls-Royce Trent 1000 series engines installed on Boeing 787 aircraft. The directive targets engines experiencing high wear on high pressure turbine triple seals, which could lead to turbine disc failure and potential damage to the aircraft. It mandates specific actions to deactivate the MAS control valves to mitigate this risk.
What Changed
This revision of EASA AD 2021-0009 excludes Trent 1000 engines that have incorporated Rolls-Royce modification 75-K778 or Service Bulletin 75-K778 from the applicability of the directive. It also recognizes the embodiment of SB 75-K778 as an acceptable alternative method of compliance, which deactivates the MAS control valves without triggering spurious engine alert messages.
Why It Matters
This directive is critical for aviation professionals to prevent potential engine failures caused by increased turbine cooling air leakage and seal fin wear. Operators and maintenance teams must ensure compliance to avoid unsafe conditions that could lead to in-flight engine damage and debris release. Understanding the updated applicability and alternative compliance methods helps streamline maintenance and operational decisions.
What To Do
Operators must deactivate the MAS control valves on affected Trent 1000 engines within 50 flight cycles from first installation or within 30 days or 100 flight cycles after 15 January 2021, whichever is later, following Rolls-Royce Alert NMSB 75-AK642 instructions. Engines modified with SB 75-K778 are exempt from these requirements. Ferry flights of up to 3 flight cycles are permitted to position aircraft for maintenance.
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