EASA AD 2021-0278R1: Powerplant — 12AK Clutch — Prohibition of Flights

What to do

Operators of Stemme S10-VT and S12 powered sailplanes with affected 12AK clutches must cease flight operations immediately from 17 December 2021 until the clutch is replaced or modified per the latest service bulletin. Installation of affected clutches on any powered sailplane is prohibited from the same date. After replacing an affected clutch with a serviceable part, the aircraft may resume operation and is reclassified accordingly. Compliance with the service bulletin revision 02 dated 18 April 2022 is required to address the unsafe condition.

Summary

EASA Airworthiness Directive 2021-0278R1 is a regulatory update addressing safety concerns for Stemme S10-VT and Stemme S12 powered sailplanes equipped with the freewheel clutch Part Number 12AK. The directive prohibits flight operations of powered sailplanes with affected clutches due to risks of clutch slipping and overheating, which could lead to total loss of thrust and potential loss of control. It applies to all serial numbers of these aircraft models and mandates compliance with Stemme AG Service Bulletin P062-980058 revisions.

What changed

This revision of EASA AD 2021-0278 updates the definition of the affected freewheel clutch parts to include those modified per Stemme Service Bulletin P062-980058 Revision 02 and re-identified with a '/M' suffix. It replaces the original emergency AD issued in December 2021 by incorporating a new clutch modification with improved friction pads to mitigate the unsafe condition. The revised AD maintains the prohibition on flight and installation of affected parts until modification is completed.

Why it matters

This directive is critical for operators and maintenance organizations as it directly impacts the airworthiness and safe operation of Stemme powered sailplanes. Compliance ensures prevention of clutch failure that could cause sudden loss of thrust and jeopardize flight safety. It also affects parts management and installation practices, requiring strict adherence to the updated service bulletin and AD requirements to maintain regulatory compliance and aircraft safety.