Hi
barit1,
One must question the style of program management that takes engine hardware which hes been intentionally abused in development test, and is then installed in a single-engine tactical aircraft. Isn't this a needless risk to a high-visibility program?
I am thinking this engine was in an aircraft being used to test various thermal paints (heat resistant) applied to some areas of tail that were receiving damage from the afterburner which swivels (not fixed in one plane). So they ran the afterburner in flight for excessive periods of time to determine which paint worked best or perhaps using a preselected paint to determine if it fixed the problem. Then at some point discovered the crack in one 3rd stage turbine blade. I am sure their first thought was oh-oh, the older blade cracking problem has returned.
Anyhow, all of this leads to some questions:
1. Why would prolonged afterburner usage have any effect on the LPT of the engine?
2. Wouldn't engine EGT monitoring result in the fuel schedule being automatically reduced if EGT was being exceeded?
A fairly early and low operating hour blade creep situation leading to creep rupture (cracking) on a single crystal turbine blade would seeming indicate one is perched on the edge of the cliff with not much margin. Perhaps this blade had a not so perfect crystal orientation that degraded creep life or the stress levels of the blade are higher than thought to be. It is hard to say, but there has to be more to the story. The reduced hours prior to borescope inspection is a good thing.
TD