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Old 9th Jan 2019, 19:45
  #18 (permalink)  
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,539
Originally Posted by old,not bold View Post

Re Q1; here's what Wiki says, which I missed.......

So that's the answer to Q1. I suppose a better answer is that any heavy vibration could have serious consequences in all sorts of ways, just one of which might be a blade fracture.
As is often the case, Wiki is over simplistic. The problem was that the newly approved higher thrust rating could cause the fan blades to go into flutter (commonly known as simply 'fan flutter'). Once fan flutter starts, the fan blades can fail in just a few seconds.
The industry learned a great deal about fan flutter in the aftermath of this accident. Now days, specific testing is performed on new or significantly changed fan blades to look for signs of fan flutter before the engine is certified.
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