Engine vibration

[Deathrow558]

Ok, please stay with me. I work for an airline but not a pilot so be patient!
Right. One of our aircraft, a 757, suffered an engine failure the other day. It was just after t/o so they circled to burn fuel, landed within their max landing weights and all was well.
Anyway, I was in the office the day after and was listening to the chief pilot discussing it over the phone. I could understand almost none of what he was saying but I picked out something about they'd had a boroscope and then they did something else and got a vibration reading of 2.8 and that 2.5 was the legal limit....something like that.
I had a look through the MEL and could find nothing. Could someone shed some light on what they were saying?
From what I've heard so far the a/c will be AOG for about 12 weeks. Which makes it even harder for me to think what could have actually happened?
Makes it even worse to think one of the engines is brand new (not sure which...the bust one?? who knows), one of them is leased, at a cost of $4000 a day on top of $400 per hour to sit at SFB. And you know what they say...an aircraft on the ground makes :mad: all...but costs a TON!

[ITCZ]

Boroscope. Bore + Scope. A long skinny gadget with a lens that can be directed through small holes to visually inspect the internals of a machine, or similar. Particularly useful for inspecting rotor and stator vanes in gas turbine engines, to see what failed.

http://www.boroscope.com/

Vibration. Unless perfectly formed and perfectly in balance, spinning masses, such as gas turbine engine components, vibrate. If a gas turbine engine rotor is unbalanced, it will vibrate. Usually expressed as inches/sec. Therefore 2.8 inches/sec.

Want to know more... not a bad explanation from http://www.patentstorm.us/patents/5934610-description.html

The modern jet engine includes several concentrically mounted shafts, each rotating at a slightly different frequency. Each of the rotating shafts or spools can include a compressor-turbine assembly which in turn includes fan and turbine blades. In the intake stages the blades are used to compress incoming air, and in the output stages the blades drive the compressor.

Machinery having massive rotating components, such as jet aircraft engines, may experience shaft bearings or shaft housing failures. In addition, these rotating components may become unbalanced and impose loads upon the bearings and housing well beyond acceptable specifications. These problems may be a result of any variety of causes which include, manufacturing defects, design defects, wear, misuse, accidental damages and the like. In the case of an aircraft while in operation, failure of these engine components can lead to, not only engine loss, but catastrophic loss of aircraft.

Vibration amplitudes and patterns, induced by the rotation of jet engine sub-components, are indicative of sub-component degradation and decreased reliability. SNIP....

Thus, vibration detection is not only an invaluable safety tool used to monitor engines while in operation, but has been incorporated into scheduled engine maintenance procedures.

[Deathrow558]

^ What a great post. Thanks :)

[slv1388]

Hi!!! I'm french (sorry for my bad english).
I'm a new user here and I'm looking for a simple borescope.

I've seen this and I want to know your opinion: boroscope (http://www.pce-france.fr/fiches-mesureurs/boroscope-pce-e130.htm)
Here are the boroscope in english: borescopes (http://www.industrial-needs.com/measuring-instruments/borescopes.htm)

Thank you in advance for your attention.