Derg:
look also at the second article mentioned:
http://www.eng.ox.ac.uk/samp/pubs/clifton_transfer.pdf and check fig 2.2 referring to trent 900 engine with data "...constructed from 200 hours of flight data recorded over a period of one month."
So the data is there BUT look at the width of the red band in the middle or rev range and at the high end. Over there there is practically no chance to detect anything viable!
i would suggest that all of us interested in turbine engines monitoring read carefully both of these articles - luckily to all of us you have been able to dug out and publish links to such extremely valuable reading. It looks like a good peek under the hood of RR maintenance program
