Barit1:
I agree with your explanation of thermal expansion/contraction in turbine engines and the consequent advantages of thermal stabilization intervals. Well put.
I would however like to comment on the following statement.
A couple of RJ pilots experienced this at FL410 a year ago with sad results (search for "core lock")
Following the public hearing held by the NTSB regarding the Pinnacle Airlines RJ crash investigation, a rather large body of data gathered during the investigation to date was made available through the NTSB website. Along with the CVR transcript and FDR traces, numerous other investigative group reports were included. One of these was the GE engines paper on "core-lock" phenomenon. Testing on the CF-34 revealed this to occur following flameout during subsequent air re-start attempts. This may or may not explain the Pinnacle crew's lack of success in accomplishing a re-start for the following reasons:
1) GEs tests did not follow a severe over-temp. The Pinnacle FDR traces indicate an ITT indication well beyond maximum limits on one of the engines during the aerodynamic stall event. (IIRC, the r/h eng.) While a severe over-temp may result in causing a rotating group to "lock up", this is a separate issue to the phenomenon addressed in GEs paper on "core-lock." "Core-locked" engines tested could be turned by the starter once internal temperatures stabilized. Often not the case with engines which have been severely over-temped to a degree that causes permanent deformation or dimensional changes of internal components.
2) From the data presented, it is not clear exactly what the configuration of the pneumatic system was at the time that re-start was attempted. We can only hope that the final report will establish the cause for the lack of success in attaining a re-start on at least one engine. I get the impression that this is one of the focal points of the investigation.
I can draw no solid conclusions regarding whether "core-lock" is a contributing factor to this accident on the basis of of my reading of the data presented. It is my hope that the final report will present the FDR data in a clearer, more readable format than the information currently available to the public on the website. While I may have reached a few of my own conclusions as to the root causes of the event, I consider many aspects of the causal chain of events to be unresolved questions. The role "core-lock may have had is one of them.
Apologies for sidetracking the thread a bit.
Best regards,
Westhawk