Old 29th Nov 2018, 21:33
  #437 (permalink)  
tdracer
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,453
With a few notable exceptions, Boeing doesn't have any recommendations regarding high engine vibrations other than 'crew awareness'. There are other potential causes for engine vibrations other than imminent engine failure - e.g. ice accumulation on the fan/compressor blades (which can usually be addressed by temporarily increasing the engine power setting).
Even when the vibrations are the result of engine damage, you don't want the FADEC unilaterally shutting the engine down - the problem could easily affect multiple engines (e.g. birdstrike) and the last thing you want to do is do an auto-shutdown of all engines.
The one exception for high vibes that I recall was for the RB211-524 engine. After a couple of bearing failure related fan shaft fractures that culminated in uncontained engine failures, if the engine vibes exceeded some threshold the crew was instructed to shut it down.
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