Damage suspected
 

When do you suspect a damage on a failed turboprop engine excepting the case you have a fire or an unusual noise from the failed engine?

As a general rule, the determining factors in deciding if the engine has suffered a "simple" flame-out, or damage which would preclude a re-start attempt are -

(1) Fire (as you've mentioned),
(2) Loss of Oil Pressure preceding the failure,
(3) Excessive EGT preceding the failure,
(4) Excessive vibration unassociated with compressor stall preceding the failure,
(5) Foreign body ingestion,
(6) Engine overspeed.

All of the above are good indicators that the engine has failed due to or associated with damage.

Regards,

Old Smokey

What about "after flame out" clues? If none of the above mentioned has been observed (not because it didn't happen, but because you didn't notice) would you try to restart the engine?
Thanks for the reply!

It's hard to miss any of the clues Old Smokey has put down. The only clue about engine damage (that I can think of, that is), after the engine has flamed out, would be oil streaks on engine nacelle or wing but it's far from reliable indication.

So would I try to restart engine if it flames out quietly or violently but unnoticed (just a hypothetical case)? Absolutely yes - using inflight restart procedure and applying caution. If vibrations start, if EGT rises fast nad high, if oil press stays low then it's start abort and single engine ops time.

O% N1 or N2 (Nh/Nl) might indicate siezed internal bits, not conducive to a restart.

Massive explosion, holes in the nacelle, smoke in cockpit, smell of hot metal, EGT in the red, Oh, and a pulse of 683, that was the real give away.

The dictionary does a good job of summing it up.
Fail = To be unsuccessful.
i.e. it doesn't work!

Take a look at this cause effect tree of engine symptoms vs cause

http://fromtheflightdeck.com/Stories/turbofan/

There is a similar tree for turboprops, but I'm hunting for the URL now.

Great link, Al Weaver. Unlike many presentations "designed by committee", this one is quite good and tells a complex story in a succinct manner.