Solution of the Non Synchronous Vibration in the AS900 Engine

The AS900 is a 7,000-lbf-thrust class medium bypass turbofan for business jet and small regional transport aircraft. During initial development testing, high non-synchronous vibration (NSV) limited AS900 engine operation in the test cells. The NSV was associated with a substantial aft end motion involving both spools, the static structure, and the aft mount system. The aft mount was modified, which allowed the engine to run at its maximum power with a moderate level of NSV. However, the presence of NSV was perceived to be a customer satisfaction issue as a potential exciter of cabin noise in the aircraft. Therefore, a comprehensive analysis and test program was initiated to eliminate NSV from the AS900 engine. This paper presents the process of identifying the root cause of the NSV and its influencing factors, as well as the design changes to successfully eliminate it from the AS900 engine.