Qantas turn backs due to "Engine vibration"

[rob_ginger]

There have been two recent turn backs of Qantas flights - reason for both reported as engine vibration.

Second Qantas flight turned back after 'vibrating' engine (http://www.smh.com.au/national/second-qantas-flight-turned-back-after-vibrating-engine-20160409-go2kmy.html)

I'm interested to know why this might be happening - I did a bit of google'ing, and found a lot of interesting stuff about the sophisticated vibration monitoring gear that's available, although not a lot of information about what's actually fitted to current generation aircraft.

It seems to me that engine vibration data would be part of the data that's continually fed back to airline maintenance. So maintenance would be able to see any trend of increasing vibration, and schedule an engine change or whatever is required to fix the issue *before* it became bad enough to warrant a turn-back. I can't believe that Qantas would be silly enough to simply ignore an increasing trend in engine vibration - must be much more expensive to turn around a plane full of passengers than take action before hand.

So can anyone enlighten me as to why engine vibration would "suddenly" increase enough to generate an ECAM warning? Could it be due to the engine ingesting something small (other than, say, Canada geese!) while in flight?

(P.S. Not a pilot, but an Engineer with a keen interest in aviation)

[ACMS]

A lot of finely balanced high speed rotating parts in a Jet Engine.........there could be many reasons why one blade or stage gets out of balance, from ingesting something to fatigue.

Vibration by itself it not necessarily a reason to shut down an Engine. You have to look deeper into the displays....

[riff_raff]

The engine instrumentation actually has some ability to determine the source of the vibration based on its characteristics like frequency. For example, each rotating section of the engine produces a particular frequency based on the number of blades, etc. If it is determined that the source of vibration is due to a serious problem in the engine, the crew would take appropriate actions.

[NSEU]

I remember on the Boeings that the air to ground reporting was not continuous, but at specific points throughout the flight. Trends were determined from one flight to another. However, if limits were exceeded, special air to ground reports were generated.

Vibrations do tend to jump about a bit even during normal ops, so trends would be hard to track. Also, some high vibration readings are due to faulty sensors/wiring, which probably won't show a trend.