Narrative:

While at cruise altitude (41,000'), noticed cabin temperature getting warmer. Selected a lower temperature on controller with no resultant decrease of 'H' valve position. Selected 'manual' mode and attempted to select lower valve position at which time 'H' valve went to wide open position and would not move. The duct overheat came on very quickly, and this is supposed to automatically dump the 'H' valve to closed. This did not happen and a strong burning smell was now coming from the cabin. The crew attempted to rectify the problem using the checklist to no avail. We asked ind center for a lower altitude and were told to stand by. We reduced power and maintained our altitude, and when center did not come back, we asked again for lower altitude and advised him at this time that we had an overheat problem and would like to begin descent as soon as possible and would like to land in cincinnati. The controller gave us an immediate lower altitude and a right turn towards louisville and suggested louisville would be closer to our present position and we told him we would like to land there instead of cincinnati. At this point the cabin was getting very warm and still with a burning smell. As we descended through 24,000', the smell and temperature started getting better and approximately 18,000' the duct overheat light went out. The controller asked a couple of times if we wished to declare an emergency and if we wanted the equipment standing by in louisville. We told we didn't think this was necessary. He then told us to squawk 7700 on our transponder, which we did and continued our descent and landing to louisville. On landing, we were met by fire equipment vehicles who followed us to the gate. We advised them of our problem and told them we no longer needed anything from them. After going inside the FBO at louisville, we were called by the FAA office on the field and an inspector asked for all pertinent information on the aircraft and crew and wanted to know why we had declared an emergency. We advised him at this time that we had not declared an emergency and upon further investigation by the inspector, he advised us that ZID had declared an emergency for us. No conflicts occurred nor did we break any regulations during this precautionary descent and landing. We felt this situation could have gotten out of hand if we had not descended, which we were able to do fairly promptly with center's help. However, we were not aware that if ATC requests you squawk 7700, you are declaring an emergency, which we felt we did not have to declare at the time.

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Original NASA ASRS Text

Title: CORPORATE LTT AT FL410 EXPERIENCES BLEED AIR DUCT OVERHEAT, DIVERTS TO A PRECAUTIONARY LNDG.

Narrative: WHILE AT CRUISE ALT (41,000'), NOTICED CABIN TEMPERATURE GETTING WARMER. SELECTED A LOWER TEMPERATURE ON CTLR WITH NO RESULTANT DECREASE OF 'H' VALVE POSITION. SELECTED 'MANUAL' MODE AND ATTEMPTED TO SELECT LOWER VALVE POSITION AT WHICH TIME 'H' VALVE WENT TO WIDE OPEN POSITION AND WOULD NOT MOVE. THE DUCT OVERHEAT CAME ON VERY QUICKLY, AND THIS IS SUPPOSED TO AUTOMATICALLY DUMP THE 'H' VALVE TO CLOSED. THIS DID NOT HAPPEN AND A STRONG BURNING SMELL WAS NOW COMING FROM THE CABIN. THE CREW ATTEMPTED TO RECTIFY THE PROBLEM USING THE CHECKLIST TO NO AVAIL. WE ASKED IND CENTER FOR A LOWER ALT AND WERE TOLD TO STAND BY. WE REDUCED POWER AND MAINTAINED OUR ALT, AND WHEN CENTER DID NOT COME BACK, WE ASKED AGAIN FOR LOWER ALT AND ADVISED HIM AT THIS TIME THAT WE HAD AN OVERHEAT PROBLEM AND WOULD LIKE TO BEGIN DSCNT ASAP AND WOULD LIKE TO LAND IN CINCINNATI. THE CTLR GAVE US AN IMMEDIATE LOWER ALT AND A RIGHT TURN TOWARDS LOUISVILLE AND SUGGESTED LOUISVILLE WOULD BE CLOSER TO OUR PRESENT POSITION AND WE TOLD HIM WE WOULD LIKE TO LAND THERE INSTEAD OF CINCINNATI. AT THIS POINT THE CABIN WAS GETTING VERY WARM AND STILL WITH A BURNING SMELL. AS WE DESCENDED THROUGH 24,000', THE SMELL AND TEMPERATURE STARTED GETTING BETTER AND APPROX 18,000' THE DUCT OVERHEAT LIGHT WENT OUT. THE CTLR ASKED A COUPLE OF TIMES IF WE WISHED TO DECLARE AN EMER AND IF WE WANTED THE EQUIPMENT STANDING BY IN LOUISVILLE. WE TOLD WE DIDN'T THINK THIS WAS NECESSARY. HE THEN TOLD US TO SQUAWK 7700 ON OUR TRANSPONDER, WHICH WE DID AND CONTINUED OUR DSCNT AND LNDG TO LOUISVILLE. ON LNDG, WE WERE MET BY FIRE EQUIPMENT VEHICLES WHO FOLLOWED US TO THE GATE. WE ADVISED THEM OF OUR PROBLEM AND TOLD THEM WE NO LONGER NEEDED ANYTHING FROM THEM. AFTER GOING INSIDE THE FBO AT LOUISVILLE, WE WERE CALLED BY THE FAA OFFICE ON THE FIELD AND AN INSPECTOR ASKED FOR ALL PERTINENT INFO ON THE ACFT AND CREW AND WANTED TO KNOW WHY WE HAD DECLARED AN EMER. WE ADVISED HIM AT THIS TIME THAT WE HAD NOT DECLARED AN EMER AND UPON FURTHER INVESTIGATION BY THE INSPECTOR, HE ADVISED US THAT ZID HAD DECLARED AN EMER FOR US. NO CONFLICTS OCCURRED NOR DID WE BREAK ANY REGS DURING THIS PRECAUTIONARY DSCNT AND LNDG. WE FELT THIS SITUATION COULD HAVE GOTTEN OUT OF HAND IF WE HAD NOT DESCENDED, WHICH WE WERE ABLE TO DO FAIRLY PROMPTLY WITH CENTER'S HELP. HOWEVER, WE WERE NOT AWARE THAT IF ATC REQUESTS YOU SQUAWK 7700, YOU ARE DECLARING AN EMER, WHICH WE FELT WE DID NOT HAVE TO DECLARE AT THE TIME.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.