Narrative:

I was the flight instrument on a flight in an small aircraft X. The aircraft had been used for 1.4 hours flight and exhibited no problems during this flight. Fuel was added to the aircraft after this first flight and fuel samples were taken during the preflight inspection to ensure that the fuel was free from contaminants. The fuel tanks were nearly full at the start of this second lesson. This second lesson involved a flight to huntsville carl T. Jones field where .9 hours was consumed in traffic pattern takeoffs and lndgs. On the return trip to the south huntsville airport, the aircraft experienced a sudden loss of power. The aircraft was at 1500' MSL at 2250 RPM and was indicating 95 NM/hour. The aircraft had been at this altitude and power setting since leaving the jones field. The power loss stated involved a sudden drop in RPM from 2250 to below 1000 almost immediately. With this drastic loss of power, it was impossible to maintain altitude and a landing was necessary. I took control of the aircraft and executed a landing on a deserted, paved, 2-LANE county road. There was no personal injury, property damage or substantial aircraft damage. The act personnel handling the aircraft flight were notified and a similar notification was made to the local flight standards office. I was advised that no further report from me was necessary. At the time of this difficulty the mixture was set to the full rich position, the primer was secured, the mags were confirmed in the both position and the engine instruments, ie, oil temperature and pressure, were well within the green operational limits. Maintenance personnel inspected the aircraft and found all linkages and controls to be operational. The engine run up and performance at the landing sight were normal and the aircraft was flown to the south huntsville airport where additional inspections did not reveal a cause for this landing. This was the second incident within the same month (july) requiring an unscheduled landing. The previous incident involved small aircraft Y. Post landing inspection of the small aircraft Y revealed water contamination within the fuel system which was undetectable during the preflight inspections. There was no suggested link between these 2 incidents as no contamination was found during inspections of the small aircraft X. Fuel from the small aircraft X was inspected before the flight, after the landing and again during an inspection of the aircraft at the south huntsville airport. Fuel remaining in the small aircraft X system was consistent with the use expected during 1.2 hours operation. Carburetor ice was not suspected as a possible cause given the dramatic loss of power and the only suspected explanation I have had suggested was that some form of foreign material was injected into the venturi area where it was consumed through the engine. The aircraft was returned to service and has exhibited normal operation since this occurrence. Callback conversation with reporter revealed the following: the reporter indicated that a full maintenance check had not revealed the cause of the power loss, and that the aircraft had been flown approximately 85 hours west/O incident subsequent to the report's forced landing. Additional commentary by the reporter indicated that items such as the manual primer pump, magnetos, fuel selector and mixture were checked as part of the emergency procedure, the carburetor heat was never applied. The reporter commented that as the power loss was very sudden, a situation not associated with carburetor icing, he did not attempt to apply carburetor heat. He also admitted that the procedure he utilized at engine power loss was at variance with standard emergency procedures that he taught his students. Maintenance personnel indicated a slight possibility that fibrous insulating material in the vicinity of the carburetor air intake could have been ingested by and blocked the venturi causing the power loss, and subsequently been passed completely through the engine.

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Original NASA ASRS Text

Title: LIGHT ACFT EXPERIENCES ENGINE POWER LOSS RESULTING IN A FORCED LNDG.

Narrative: I WAS THE FLT INSTR ON A FLT IN AN SMA X. THE ACFT HAD BEEN USED FOR 1.4 HRS FLT AND EXHIBITED NO PROBS DURING THIS FLT. FUEL WAS ADDED TO THE ACFT AFTER THIS FIRST FLT AND FUEL SAMPLES WERE TAKEN DURING THE PREFLT INSPECTION TO ENSURE THAT THE FUEL WAS FREE FROM CONTAMINANTS. THE FUEL TANKS WERE NEARLY FULL AT THE START OF THIS SECOND LESSON. THIS SECOND LESSON INVOLVED A FLT TO HUNTSVILLE CARL T. JONES FIELD WHERE .9 HRS WAS CONSUMED IN TFC PATTERN TKOFS AND LNDGS. ON THE RETURN TRIP TO THE SOUTH HUNTSVILLE ARPT, THE ACFT EXPERIENCED A SUDDEN LOSS OF PWR. THE ACFT WAS AT 1500' MSL AT 2250 RPM AND WAS INDICATING 95 NM/HR. THE ACFT HAD BEEN AT THIS ALT AND PWR SETTING SINCE LEAVING THE JONES FIELD. THE PWR LOSS STATED INVOLVED A SUDDEN DROP IN RPM FROM 2250 TO BELOW 1000 ALMOST IMMEDIATELY. WITH THIS DRASTIC LOSS OF PWR, IT WAS IMPOSSIBLE TO MAINTAIN ALT AND A LNDG WAS NECESSARY. I TOOK CONTROL OF THE ACFT AND EXECUTED A LNDG ON A DESERTED, PAVED, 2-LANE COUNTY ROAD. THERE WAS NO PERSONAL INJURY, PROPERTY DAMAGE OR SUBSTANTIAL ACFT DAMAGE. THE ACT PERSONNEL HANDLING THE ACFT FLT WERE NOTIFIED AND A SIMILAR NOTIFICATION WAS MADE TO THE LCL FLT STANDARDS OFFICE. I WAS ADVISED THAT NO FURTHER RPT FROM ME WAS NECESSARY. AT THE TIME OF THIS DIFFICULTY THE MIXTURE WAS SET TO THE FULL RICH POS, THE PRIMER WAS SECURED, THE MAGS WERE CONFIRMED IN THE BOTH POS AND THE ENG INSTRUMENTS, IE, OIL TEMP AND PRESSURE, WERE WELL WITHIN THE GREEN OPERATIONAL LIMITS. MAINT PERSONNEL INSPECTED THE ACFT AND FOUND ALL LINKAGES AND CONTROLS TO BE OPERATIONAL. THE ENG RUN UP AND PERFORMANCE AT THE LNDG SIGHT WERE NORMAL AND THE ACFT WAS FLOWN TO THE SOUTH HUNTSVILLE ARPT WHERE ADDITIONAL INSPECTIONS DID NOT REVEAL A CAUSE FOR THIS LNDG. THIS WAS THE SECOND INCIDENT WITHIN THE SAME MONTH (JULY) REQUIRING AN UNSCHEDULED LNDG. THE PREVIOUS INCIDENT INVOLVED SMA Y. POST LNDG INSPECTION OF THE SMA Y REVEALED WATER CONTAMINATION WITHIN THE FUEL SYS WHICH WAS UNDETECTABLE DURING THE PREFLT INSPECTIONS. THERE WAS NO SUGGESTED LINK BTWN THESE 2 INCIDENTS AS NO CONTAMINATION WAS FOUND DURING INSPECTIONS OF THE SMA X. FUEL FROM THE SMA X WAS INSPECTED BEFORE THE FLT, AFTER THE LNDG AND AGAIN DURING AN INSPECTION OF THE ACFT AT THE SOUTH HUNTSVILLE ARPT. FUEL REMAINING IN THE SMA X SYS WAS CONSISTENT WITH THE USE EXPECTED DURING 1.2 HRS OPERATION. CARB ICE WAS NOT SUSPECTED AS A POSSIBLE CAUSE GIVEN THE DRAMATIC LOSS OF PWR AND THE ONLY SUSPECTED EXPLANATION I HAVE HAD SUGGESTED WAS THAT SOME FORM OF FOREIGN MATERIAL WAS INJECTED INTO THE VENTURI AREA WHERE IT WAS CONSUMED THROUGH THE ENG. THE ACFT WAS RETURNED TO SVC AND HAS EXHIBITED NORMAL OPERATION SINCE THIS OCCURRENCE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THE RPTR INDICATED THAT A FULL MAINT CHK HAD NOT REVEALED THE CAUSE OF THE PWR LOSS, AND THAT THE ACFT HAD BEEN FLOWN APPROX 85 HRS W/O INCIDENT SUBSEQUENT TO THE RPT'S FORCED LNDG. ADDITIONAL COMMENTARY BY THE RPTR INDICATED THAT ITEMS SUCH AS THE MANUAL PRIMER PUMP, MAGNETOS, FUEL SELECTOR AND MIXTURE WERE CHKED AS PART OF THE EMER PROC, THE CARB HEAT WAS NEVER APPLIED. THE RPTR COMMENTED THAT AS THE PWR LOSS WAS VERY SUDDEN, A SITUATION NOT ASSOCIATED WITH CARB ICING, HE DID NOT ATTEMPT TO APPLY CARB HEAT. HE ALSO ADMITTED THAT THE PROC HE UTILIZED AT ENG PWR LOSS WAS AT VARIANCE WITH STANDARD EMER PROCS THAT HE TAUGHT HIS STUDENTS. MAINT PERSONNEL INDICATED A SLIGHT POSSIBILITY THAT FIBROUS INSULATING MATERIAL IN THE VICINITY OF THE CARBURETOR AIR INTAKE COULD HAVE BEEN INGESTED BY AND BLOCKED THE VENTURI CAUSING THE PWR LOSS, AND SUBSEQUENTLY BEEN PASSED COMPLETELY THROUGH THE ENG.

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.