Trent 972
The Key Document Faa A.c. 33.63-1, then perhaps you should also give consideration to paragraph 2b. on the first page. ie.
If you refer to the master certification document:
PART 33—AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES
You will note under "vibration", it basically states (my wording, not verbatim) that adequate testing must be done to demonstrate vibration is not a problem. So then, the circular about this subject is issued to "guide" the requester through the process of testing for vibration during the certification process as there may have been many questions in past and present regarding what is acceptable to the FAA. The circular implies "Here is a way to accomplish vibration testing that is acceptable to us, but there are other way that may be acceptable as well." It is a unhappy day to have spent $1M or $2M on an engine test to only learn it didn't meet the certification criteria in the FAA's eyes.
Turbine D