Originally Posted by
albatross
Just an aside.
I have always wondered why, in some instances, a part that has worked well for years, suddenly does not.
Change in supplier, overhaul process ect?
I recall, for example, in the late 70s we suddenly had problems with Allison 250 engines. What had changed?
Usually a process or supplier change upstream in the supply chain. If it is believed by the OEM to be manufacturing to the same specification then no re-proving is required as would be the case in initial certification (if they are even required to be told). It can be driven by raw material availability, cost or process "improvement" (ie efficiency of production). I've even seen Human Factors where the old boy doing inspection retires and is replaced by a new pup. A lot of piece part supply in aerospace supply chains that ends up on Tier 1 product is supplied by surprisingly Mom'n'Pop outfits. You would hope that critical path items would be subject to extra scrutiny no matter how low-tech but that isn't always the case.