Until the advent of the 501-K34 engine the 501 did not have a history of high vibration levels. When the 501-K17 did exhibit high vibration levels, predictably, there was an identifiable cause. A few years after the introduction of the 501-K34, high levels of engine start vibration were frequently observed. Normally this would occur during engine “cold” start. When the 501-K34 was started “warm” or “hot” much lower engine start vibration levels were observed. This paper discusses 501-K vibration in general and the US Navy investigation into the mechanical causes for the high “cold start” 501-K34 vibration, as well as data analysis and problem mitigation. Because of the number of 501-K34s that have exhibited this problem and still appeared to be operating adequately, in other respects, the USN, over the last 7 years, to ensure the continued reliability of the 501-K34 engine has been monitoring remotely vibration and other important engine parameters. This was done through Integrated Performance Analysis Reports (IPAR), the Maintenance Engineering Library Server (MELS) and by accessing engine parameter data from the Full Authority Digital Controller (FADC). Using remote monitoring and understanding the vibrations mechanical aspects, it was realized that the 501-K34 could operate for a considerable period with high “cold start” vibration levels before the accumulated effect of this distress resulted in engine removal and subsequent repair.
The Chain Gang