Narrative:

An abrupt partial loss of power was experienced, accompanied by roughness, a change in the sound of the engine, and the loss of about 50 engine RPM's. Because of my particular location, after engaging carburetor heat and checking switch and valve position I unhesitantly dialed 7700 into my transponder and declared an emergency. Had the loss of power led to immediate total engine failure, I felt there was a slight chance that I would not have been able to glide to an airport, and I felt it important that our precise whereabouts be known. I tried carburetor heat, a magneto check, and altered mixture settings, none of which had any significant effect upon the condition. Although a glide to the nearest airport was soon assured, I elected to not cancel the emergency until after landing because I had not been able to diagnose the problem in-flight. Finding myself over the nearest airport (mariposa) with an altitude loss of only 1500 ft, and still producing power, I elected to continue to merced, provided that I could assure myself to be within an easy glide of either airport before committing to merced. The landing at merced was uneventful. Mechanical support services were not available on the field. The following day I removed the engine cowl and found the problem to have been nothing more than a break in a tailpipe. In order to expedite the repair during daylight hours, I elected to remove the affected part myself in preparation for the mechanic's later arrival with a replacement part. I flew the aircraft to its home base (sts) the following morning.

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Original NASA ASRS Text

Title: AN SMA ACFT IN CRUISE DECLARED AN EMER AND DIVERTED DUE TO ENG PWR DECREASING CAUSED BY A BROKEN EXHAUST PIPE.

Narrative: AN ABRUPT PARTIAL LOSS OF PWR WAS EXPERIENCED, ACCOMPANIED BY ROUGHNESS, A CHANGE IN THE SOUND OF THE ENG, AND THE LOSS OF ABOUT 50 ENG RPM'S. BECAUSE OF MY PARTICULAR LOCATION, AFTER ENGAGING CARB HEAT AND CHKING SWITCH AND VALVE POS I UNHESITANTLY DIALED 7700 INTO MY XPONDER AND DECLARED AN EMER. HAD THE LOSS OF PWR LED TO IMMEDIATE TOTAL ENG FAILURE, I FELT THERE WAS A SLIGHT CHANCE THAT I WOULD NOT HAVE BEEN ABLE TO GLIDE TO AN ARPT, AND I FELT IT IMPORTANT THAT OUR PRECISE WHEREABOUTS BE KNOWN. I TRIED CARB HEAT, A MAGNETO CHK, AND ALTERED MIXTURE SETTINGS, NONE OF WHICH HAD ANY SIGNIFICANT EFFECT UPON THE CONDITION. ALTHOUGH A GLIDE TO THE NEAREST ARPT WAS SOON ASSURED, I ELECTED TO NOT CANCEL THE EMER UNTIL AFTER LNDG BECAUSE I HAD NOT BEEN ABLE TO DIAGNOSE THE PROB INFLT. FINDING MYSELF OVER THE NEAREST ARPT (MARIPOSA) WITH AN ALT LOSS OF ONLY 1500 FT, AND STILL PRODUCING PWR, I ELECTED TO CONTINUE TO MERCED, PROVIDED THAT I COULD ASSURE MYSELF TO BE WITHIN AN EASY GLIDE OF EITHER ARPT BEFORE COMMITTING TO MERCED. THE LNDG AT MERCED WAS UNEVENTFUL. MECHANICAL SUPPORT SVCS WERE NOT AVAILABLE ON THE FIELD. THE FOLLOWING DAY I REMOVED THE ENG COWL AND FOUND THE PROB TO HAVE BEEN NOTHING MORE THAN A BREAK IN A TAILPIPE. IN ORDER TO EXPEDITE THE REPAIR DURING DAYLIGHT HRS, I ELECTED TO REMOVE THE AFFECTED PART MYSELF IN PREPARATION FOR THE MECH'S LATER ARR WITH A REPLACEMENT PART. I FLEW THE ACFT TO ITS HOME BASE (STS) THE FOLLOWING MORNING.

Data retrieved from NASA's ASRS site as of July 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.