Narrative:

On dec/wed/94 at approximately XA30 local, my copilot and I were flying our piper cherokee warrior on an IFR flight plan about 12 NM nne of rdu on a vector to intercept V-155 northbound at 5000 ft MSL, when we experienced a partial engine power failure. The engine suddenly lost about 400 RPM (fixed pitch propeller) and started running quite rough. We immediately turned back (south) to rdu and notified rdu approach control of the problem. Approach asked if we wanted to declare an emergency, and I responded in the affirmative. We were given a vector direct toward rdu and cleared for a visual approach to runway 23L. We were allowed to remain as high as we wanted on the approach. I set the fuel mixture to full rich with the throttle wide open and turned on the electric fuel pump. I checked the oil pressure and temperature (ok), the magnetos (ok), carburetor heat (ok), fuel pressure and quantity (ok) and concluded the engine had suffered a mechanical problem -- probably involving 1 cylinder. We were descending at approximately 200 FPM while maintaining near normal cruise airspeed. We were handed off to rdu tower and given an immediate clearance to land on runway 23L. I executed a higher than normal approach to the runway (7500 ft in length) and landed uneventfully. As we turned off the runway, we were met by the fire and rescue crew who followed us to the FBO. We were informed that we were trailing smoke, especially when we changed power settings. When we opened the engine cowling, we noticed oil dripping on the exhaust pipe of cylinder #3. An aviation mechanic removed the 2 spark plugs from cylinder #3. They showed obvious physical damage. The preliminary analysis is that the exhaust valve in cylinder #3 broke. It is clear that the engine was operating on 3 out of 4 cylinders during the approach. The engine was approaching its recommended time between overhaul (approximately 1960 hours out of 2000 hours time between overhaul). Up until this incident, except for using oil at a rate commensurate with the time on the engine, the engine operated and performed normally. A major engine overhaul will be performed before the aircraft is flown again. The priority treatment we received from all ATC personnel was very welcome and appreciated. We believe we did not unduly disrupt operations at rdu airport, and we have nothing but praise for the treatment we received from ATC and the fire/rescue crew. We are not aware of any abnormalities with the engine or its operation which would have caused this problem. We await an analysis of the engine after teardown.

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Original NASA ASRS Text

Title: PARTIAL ENG FAILURE AND EMER LNDG.

Narrative: ON DEC/WED/94 AT APPROX XA30 LCL, MY COPLT AND I WERE FLYING OUR PIPER CHEROKEE WARRIOR ON AN IFR FLT PLAN ABOUT 12 NM NNE OF RDU ON A VECTOR TO INTERCEPT V-155 NBOUND AT 5000 FT MSL, WHEN WE EXPERIENCED A PARTIAL ENG PWR FAILURE. THE ENG SUDDENLY LOST ABOUT 400 RPM (FIXED PITCH PROP) AND STARTED RUNNING QUITE ROUGH. WE IMMEDIATELY TURNED BACK (S) TO RDU AND NOTIFIED RDU APCH CTL OF THE PROB. APCH ASKED IF WE WANTED TO DECLARE AN EMER, AND I RESPONDED IN THE AFFIRMATIVE. WE WERE GIVEN A VECTOR DIRECT TOWARD RDU AND CLRED FOR A VISUAL APCH TO RWY 23L. WE WERE ALLOWED TO REMAIN AS HIGH AS WE WANTED ON THE APCH. I SET THE FUEL MIXTURE TO FULL RICH WITH THE THROTTLE WIDE OPEN AND TURNED ON THE ELECTRIC FUEL PUMP. I CHKED THE OIL PRESSURE AND TEMP (OK), THE MAGNETOS (OK), CARB HEAT (OK), FUEL PRESSURE AND QUANTITY (OK) AND CONCLUDED THE ENG HAD SUFFERED A MECHANICAL PROB -- PROBABLY INVOLVING 1 CYLINDER. WE WERE DSNDING AT APPROX 200 FPM WHILE MAINTAINING NEAR NORMAL CRUISE AIRSPD. WE WERE HANDED OFF TO RDU TWR AND GIVEN AN IMMEDIATE CLRNC TO LAND ON RWY 23L. I EXECUTED A HIGHER THAN NORMAL APCH TO THE RWY (7500 FT IN LENGTH) AND LANDED UNEVENTFULLY. AS WE TURNED OFF THE RWY, WE WERE MET BY THE FIRE AND RESCUE CREW WHO FOLLOWED US TO THE FBO. WE WERE INFORMED THAT WE WERE TRAILING SMOKE, ESPECIALLY WHEN WE CHANGED PWR SETTINGS. WHEN WE OPENED THE ENG COWLING, WE NOTICED OIL DRIPPING ON THE EXHAUST PIPE OF CYLINDER #3. AN AVIATION MECH REMOVED THE 2 SPARK PLUGS FROM CYLINDER #3. THEY SHOWED OBVIOUS PHYSICAL DAMAGE. THE PRELIMINARY ANALYSIS IS THAT THE EXHAUST VALVE IN CYLINDER #3 BROKE. IT IS CLR THAT THE ENG WAS OPERATING ON 3 OUT OF 4 CYLINDERS DURING THE APCH. THE ENG WAS APCHING ITS RECOMMENDED TIME BTWN OVERHAUL (APPROX 1960 HRS OUT OF 2000 HRS TIME BTWN OVERHAUL). UP UNTIL THIS INCIDENT, EXCEPT FOR USING OIL AT A RATE COMMENSURATE WITH THE TIME ON THE ENG, THE ENG OPERATED AND PERFORMED NORMALLY. A MAJOR ENG OVERHAUL WILL BE PERFORMED BEFORE THE ACFT IS FLOWN AGAIN. THE PRIORITY TREATMENT WE RECEIVED FROM ALL ATC PERSONNEL WAS VERY WELCOME AND APPRECIATED. WE BELIEVE WE DID NOT UNDULY DISRUPT OPS AT RDU ARPT, AND WE HAVE NOTHING BUT PRAISE FOR THE TREATMENT WE RECEIVED FROM ATC AND THE FIRE/RESCUE CREW. WE ARE NOT AWARE OF ANY ABNORMALITIES WITH THE ENG OR ITS OP WHICH WOULD HAVE CAUSED THIS PROB. WE AWAIT AN ANALYSIS OF THE ENG AFTER TEARDOWN.

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.