Narrative:

Communications with the sbp tower had already been established over the town of morro bay. A partial loss of engine power accompanied by fluctuations of the fuel flow and RPM were encountered. Pilot had determined fuel quantity prior to takeoff to have been 18 gallons and calculated approximately 8 gallons remained. Gauges showed 1/8 in level flight. Mixture setting was increased to full rich and an attempt to reestablish normal power was done by use and changing aircraft attitude and use of auxiliary pump. The tower was advised by the pilot that a partial loss of power had been encountered but that flight could be continued to the san luis obispo airport. Normal engine power was not achieved by the time the aircraft was 2 mi from the airport at approximately 3500 ft. The pilot elected to declare an emergency and advised the tower that a landing would be made on runway 11. On the final glide from 1700 ft MSL and approximately 1/2 mi from the approach end of runway 11, the pilot elected to shut down the engine and stop the propeller from windmilling to assure maximum glide, least drag on final flare and prevent damage to the crankshaft and engine in the event the landing was not entirely successful. The pilot advised the tower of an expected delay on the runway after touchdown. After touchdown, the pilot advised landing was successful, no damage had occurred to the aircraft or occupants and that the radios would be turned off. The pilot and passenger pushed the aircraft to the departure end of the runway. The aircraft was towed in by maintenance personnel. The fuel was drained from the system and inspected. The pilot found 6 gallons of fuel remained in the system. The fuel was void of any observed contaminants. The pilot had a mechanic inspect the fuel screen, injectors, engine driven pump and auxiliary fuel pump. A ground test and subsequent flight test demonstrated the system were operational. It is suspected that an air vapor lock may have disrupted the continuous fuel flow to the engine. The aircraft manufacturer does not provide specifications for ridding vapor lock in-flight or conditions which vapor lock could arise. Recommendations would be to avoid steep turns or slipping the aircraft when less than 1/4 tank fuel remain in the fuel tanks. This would equate to 5 gallons in each wing tank plus 3 gallons for the inverted header tank or total of 13 gallons. This fuel quantity would provide 45-60 mins of normal cruise flight. Suggested use of the auxiliary pump for conditions other than starting the engine or when the engine driven pump fails could be explained in greater detail so that pilots would be more knowledgeable about the pros and cons of using the auxiliary pump to purge an air lock in-flight.

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Original NASA ASRS Text

Title: SMA PLT HAS FLUCTUATING PWR, MAKES IT TO THE ARPT.

Narrative: COMS WITH THE SBP TWR HAD ALREADY BEEN ESTABLISHED OVER THE TOWN OF MORRO BAY. A PARTIAL LOSS OF ENG PWR ACCOMPANIED BY FLUCTUATIONS OF THE FUEL FLOW AND RPM WERE ENCOUNTERED. PLT HAD DETERMINED FUEL QUANTITY PRIOR TO TKOF TO HAVE BEEN 18 GALLONS AND CALCULATED APPROX 8 GALLONS REMAINED. GAUGES SHOWED 1/8 IN LEVEL FLT. MIXTURE SETTING WAS INCREASED TO FULL RICH AND AN ATTEMPT TO REESTABLISH NORMAL PWR WAS DONE BY USE AND CHANGING ACFT ATTITUDE AND USE OF AUX PUMP. THE TWR WAS ADVISED BY THE PLT THAT A PARTIAL LOSS OF PWR HAD BEEN ENCOUNTERED BUT THAT FLT COULD BE CONTINUED TO THE SAN LUIS OBISPO ARPT. NORMAL ENG PWR WAS NOT ACHIEVED BY THE TIME THE ACFT WAS 2 MI FROM THE ARPT AT APPROX 3500 FT. THE PLT ELECTED TO DECLARE AN EMER AND ADVISED THE TWR THAT A LNDG WOULD BE MADE ON RWY 11. ON THE FINAL GLIDE FROM 1700 FT MSL AND APPROX 1/2 MI FROM THE APCH END OF RWY 11, THE PLT ELECTED TO SHUT DOWN THE ENG AND STOP THE PROP FROM WINDMILLING TO ASSURE MAX GLIDE, LEAST DRAG ON FINAL FLARE AND PREVENT DAMAGE TO THE CRANKSHAFT AND ENG IN THE EVENT THE LNDG WAS NOT ENTIRELY SUCCESSFUL. THE PLT ADVISED THE TWR OF AN EXPECTED DELAY ON THE RWY AFTER TOUCHDOWN. AFTER TOUCHDOWN, THE PLT ADVISED LNDG WAS SUCCESSFUL, NO DAMAGE HAD OCCURRED TO THE ACFT OR OCCUPANTS AND THAT THE RADIOS WOULD BE TURNED OFF. THE PLT AND PAX PUSHED THE ACFT TO THE DEP END OF THE RWY. THE ACFT WAS TOWED IN BY MAINT PERSONNEL. THE FUEL WAS DRAINED FROM THE SYS AND INSPECTED. THE PLT FOUND 6 GALLONS OF FUEL REMAINED IN THE SYS. THE FUEL WAS VOID OF ANY OBSERVED CONTAMINANTS. THE PLT HAD A MECH INSPECT THE FUEL SCREEN, INJECTORS, ENG DRIVEN PUMP AND AUX FUEL PUMP. A GND TEST AND SUBSEQUENT FLT TEST DEMONSTRATED THE SYS WERE OPERATIONAL. IT IS SUSPECTED THAT AN AIR VAPOR LOCK MAY HAVE DISRUPTED THE CONTINUOUS FUEL FLOW TO THE ENG. THE ACFT MANUFACTURER DOES NOT PROVIDE SPECS FOR RIDDING VAPOR LOCK INFLT OR CONDITIONS WHICH VAPOR LOCK COULD ARISE. RECOMMENDATIONS WOULD BE TO AVOID STEEP TURNS OR SLIPPING THE ACFT WHEN LESS THAN 1/4 TANK FUEL REMAIN IN THE FUEL TANKS. THIS WOULD EQUATE TO 5 GALLONS IN EACH WING TANK PLUS 3 GALLONS FOR THE INVERTED HEADER TANK OR TOTAL OF 13 GALLONS. THIS FUEL QUANTITY WOULD PROVIDE 45-60 MINS OF NORMAL CRUISE FLT. SUGGESTED USE OF THE AUX PUMP FOR CONDITIONS OTHER THAN STARTING THE ENG OR WHEN THE ENG DRIVEN PUMP FAILS COULD BE EXPLAINED IN GREATER DETAIL SO THAT PLTS WOULD BE MORE KNOWLEDGEABLE ABOUT THE PROS AND CONS OF USING THE AUX PUMP TO PURGE AN AIR LOCK INFLT.

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.