Airworthiness Directives; Stemme AG Gliders

We propose to supersede Airworthiness Directive (AD) 2017-10- 11 for Stemme AG Model Stemme S10-VT gliders (type certificate previously held by Stemme GmbH & Co. KG). This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as certain propeller front transmission gear wheels having insufficient material strength because of improper heat treatment during manufacturing. We are issuing this proposed AD to require actions to address the unsafe condition on these products and to add Stemme AG Model Stemme S 12 to the applicability.