Narrative:

Freezing conditions at grand canyon airport probably contributed to the deterioration of the gas cap seals on my small aircraft (original small aircraft flush mounted caps). Unknown to me, gas was being siphoned out through the gas caps (mostly from the right tank). After nearly 3 hours of flying, the fuel totalizer indicated that I had used 35 gallons with 45 gallons of fuel remaining. The left fuel gauge was showing that the left tank was nearly empty. This was slightly lower than I expected even though I had been running mostly from the left tank. The right fuel gauge however, was still showing nearly full, and slightly higher than what I expected. At that time I looked for leaking fuel but did not see any. I decided to cut my flight short to investigate by landing at la junta, approximately 25 mi ahead. A few mins later, the engine died of fuel starvation. I contacted pueblo approach on 121.5 (and later on 120.1). The controller suggested fowler field about 10-12 mi to the north. (I was approximately 29 NM southeast of pueblo VOR on the 134 degree radial.) I determined that both fowler and nearby melon were out of gliding range. The paved road below looked like a good landing spot, with surrounding fields as a backup if power lines or other obstructions prevented use of the road. Switching to the both tank position did not restart the engine, but using the electric boost pump restarted the engine. The restart gave me enough altitude that I thought I could glide to melon field now about 7 mi northeast. The controller was generally helpful except at 1 point where he said that melon was 12 O'clock at 1 mi, when it was really 5 mi away. He eventually corrected himself, but this added to the difficulty of finding a fairly hard to see strip. When I finally saw melon, it was 3 or 4 mi away. At about 2 mi from melon, I realized I was going to be about 1/2 a mi short, and elected to land in a nearby alfalfa field. Pilots at melon saw me land and came out to help. After we discovered the fuel leak and determined that the airplane was out of gas, they went back to melon to get gas. I also noticed that the fuel bladders had floated up towards the top of the tank, explaining the erroneous fuel gauge readings. With 10 gallons of gas added, and permission from the farmer, I took off from the field and landed at melon airport. To help getting off the short and muddy field, my passenger and some of our baggage went to melon by car. We fueled up with an additional 72.3 gallons, verifying that the airplane had run out of gas. (Fuel capacity is specified as 80 gallons total.) we then went on our way, after being careful that the fuel caps were installed properly. However, we could see that fuel was still leaking overboard. We landed at lamar, co, where a mechanic replaced 2 of our fuel caps with a similar kind. We were able to continue the flight the next morning, however, I suspect that small amounts of fuel were still leaking. After hearing of the many problems reported with the flush fuel caps, I have decided to replace them with an after- market replacement that includes an anti-siphon valve, which will prevent loss of fuel even if the gas cap is left off. Callback conversation with reporter revealed the following information: reporter states he has heard since his incident that half the manufacturer's small transport's have replacement caps. Manufacturer does not make these flush caps any longer but has a replacement which reporter installed. Another manufacturer makes the anti-siphon valve which works like the metal flapper valve in cars to prevent reverse flow of fuel.

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Original NASA ASRS Text

Title: FLUSH TYPE GAS CAP HAS SEAL DETERIORATION WHICH ALLOWS GAS TO SIPHON IN FLT. FAULTY FUEL INDICATION. ENG QUITS. FORCED LNDG.

Narrative: FREEZING CONDITIONS AT GRAND CANYON ARPT PROBABLY CONTRIBUTED TO THE DETERIORATION OF THE GAS CAP SEALS ON MY SMA (ORIGINAL SMA FLUSH MOUNTED CAPS). UNKNOWN TO ME, GAS WAS BEING SIPHONED OUT THROUGH THE GAS CAPS (MOSTLY FROM THE R TANK). AFTER NEARLY 3 HRS OF FLYING, THE FUEL TOTALIZER INDICATED THAT I HAD USED 35 GALLONS WITH 45 GALLONS OF FUEL REMAINING. THE L FUEL GAUGE WAS SHOWING THAT THE L TANK WAS NEARLY EMPTY. THIS WAS SLIGHTLY LOWER THAN I EXPECTED EVEN THOUGH I HAD BEEN RUNNING MOSTLY FROM THE L TANK. THE R FUEL GAUGE HOWEVER, WAS STILL SHOWING NEARLY FULL, AND SLIGHTLY HIGHER THAN WHAT I EXPECTED. AT THAT TIME I LOOKED FOR LEAKING FUEL BUT DID NOT SEE ANY. I DECIDED TO CUT MY FLT SHORT TO INVESTIGATE BY LNDG AT LA JUNTA, APPROX 25 MI AHEAD. A FEW MINS LATER, THE ENG DIED OF FUEL STARVATION. I CONTACTED PUEBLO APCH ON 121.5 (AND LATER ON 120.1). THE CTLR SUGGESTED FOWLER FIELD ABOUT 10-12 MI TO THE N. (I WAS APPROX 29 NM SE OF PUEBLO VOR ON THE 134 DEG RADIAL.) I DETERMINED THAT BOTH FOWLER AND NEARBY MELON WERE OUT OF GLIDING RANGE. THE PAVED ROAD BELOW LOOKED LIKE A GOOD LNDG SPOT, WITH SURROUNDING FIELDS AS A BACKUP IF PWR LINES OR OTHER OBSTRUCTIONS PREVENTED USE OF THE ROAD. SWITCHING TO THE BOTH TANK POS DID NOT RESTART THE ENG, BUT USING THE ELECTRIC BOOST PUMP RESTARTED THE ENG. THE RESTART GAVE ME ENOUGH ALT THAT I THOUGHT I COULD GLIDE TO MELON FIELD NOW ABOUT 7 MI NE. THE CTLR WAS GENERALLY HELPFUL EXCEPT AT 1 POINT WHERE HE SAID THAT MELON WAS 12 O'CLOCK AT 1 MI, WHEN IT WAS REALLY 5 MI AWAY. HE EVENTUALLY CORRECTED HIMSELF, BUT THIS ADDED TO THE DIFFICULTY OF FINDING A FAIRLY HARD TO SEE STRIP. WHEN I FINALLY SAW MELON, IT WAS 3 OR 4 MI AWAY. AT ABOUT 2 MI FROM MELON, I REALIZED I WAS GOING TO BE ABOUT 1/2 A MI SHORT, AND ELECTED TO LAND IN A NEARBY ALFALFA FIELD. PLTS AT MELON SAW ME LAND AND CAME OUT TO HELP. AFTER WE DISCOVERED THE FUEL LEAK AND DETERMINED THAT THE AIRPLANE WAS OUT OF GAS, THEY WENT BACK TO MELON TO GET GAS. I ALSO NOTICED THAT THE FUEL BLADDERS HAD FLOATED UP TOWARDS THE TOP OF THE TANK, EXPLAINING THE ERRONEOUS FUEL GAUGE READINGS. WITH 10 GALLONS OF GAS ADDED, AND PERMISSION FROM THE FARMER, I TOOK OFF FROM THE FIELD AND LANDED AT MELON ARPT. TO HELP GETTING OFF THE SHORT AND MUDDY FIELD, MY PAX AND SOME OF OUR BAGGAGE WENT TO MELON BY CAR. WE FUELED UP WITH AN ADDITIONAL 72.3 GALLONS, VERIFYING THAT THE AIRPLANE HAD RUN OUT OF GAS. (FUEL CAPACITY IS SPECIFIED AS 80 GALLONS TOTAL.) WE THEN WENT ON OUR WAY, AFTER BEING CAREFUL THAT THE FUEL CAPS WERE INSTALLED PROPERLY. HOWEVER, WE COULD SEE THAT FUEL WAS STILL LEAKING OVERBOARD. WE LANDED AT LAMAR, CO, WHERE A MECH REPLACED 2 OF OUR FUEL CAPS WITH A SIMILAR KIND. WE WERE ABLE TO CONTINUE THE FLT THE NEXT MORNING, HOWEVER, I SUSPECT THAT SMALL AMOUNTS OF FUEL WERE STILL LEAKING. AFTER HEARING OF THE MANY PROBLEMS RPTED WITH THE FLUSH FUEL CAPS, I HAVE DECIDED TO REPLACE THEM WITH AN AFTER- MARKET REPLACEMENT THAT INCLUDES AN ANTI-SIPHON VALVE, WHICH WILL PREVENT LOSS OF FUEL EVEN IF THE GAS CAP IS LEFT OFF. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HE HAS HEARD SINCE HIS INCIDENT THAT HALF THE MANUFACTURER'S SMT'S HAVE REPLACEMENT CAPS. MANUFACTURER DOES NOT MAKE THESE FLUSH CAPS ANY LONGER BUT HAS A REPLACEMENT WHICH RPTR INSTALLED. ANOTHER MANUFACTURER MAKES THE ANTI-SIPHON VALVE WHICH WORKS LIKE THE METAL FLAPPER VALVE IN CARS TO PREVENT REVERSE FLOW OF FUEL.

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.