Narrative:

At about 6 mi out; approaching downwind leg; noticed that the fuel pressure gauge was vibrating. In this aircraft; the fuel pressure had always been steady in the green region. I was intending to land anyway; so continued the approach. When the electric fuel pump was turned on; the vibration continued; but the average pressure rose slightly. In this aircraft the electric fuel pump had never caused the fuel gauge to rise or to move in any way. In summary; 2 differences from normal: a rapid vibration; and a slight rise when the electric fuel pump was turned on along with continued vibration. After landing; I asked the local mechanic to come and look at the indications. He climbed into the cockpit and observed the symptoms. Then we shut down the engine and attempted a restart (with electric fuel pump off as per normal procedure). As the engine turned over on starter power; the fuel pressure was seen to jump up and then fall completely to zero in rapid succession. The mechanic's conclusion (which was correct upon disassembly) was that one side of the fuel pump had failed and that the other side was pumping fuel. What was unknown from the cockpit; however; was that the diaphragm between the fuel system and the accessory box in the engine had ruptured and that fuel was being pumped directly into the accessory section. The oil tank; which had been at 7 quarts upon takeoff 1 hour or so before at takeoff; now contained 10 quarts of highly diluted oil. 2 other facts: 1) I do not know exactly how long the gauge had been vibrating before I noticed it about 5 mins before landing. 2) the aircraft had had an oil change only 2 flight hours before; yet the mechanic said the oil was very dirty ('as dirty as 50 hour oil'); indicating that the gasoline had acted as a solvent for any 'dirty' parts of the engine. At best; the diluted oil was not good for the engine. I do not know the extent of any fire hazard. I am told that if the flight had continued; the gasoline/oil mixture would be drained out of the breather tube underneath the aircraft. But it would become more and more diluted as time progressed with potential damage to the engine; not to mention the effect on range due to the loss of the fuel. No pilot that I have talked to had ever realized the potential danger of a vibrating fuel gauge. If I had been on a cross country; I would have continued to destination. I think most pilots; who have not had this experience; would also; with unpredictable results. The experienced mechanic said that in his entire experience of decades; this was the second failure of a fuel pump. In my approximately 7000 hours; much in multiple engines; it is my first. This is a rare but potentially dangerous failure. Callback conversation with reporter revealed the following information: reporter stated that the fuel pump in question was installed on a lycoming io-360 engine. Reporter advised that he did not notice any difference in engine performance in-flight and also stated that his aircraft did not have a cylinder head temperature gauge. Reporter states that he recently learned about a lycoming mandatory service bulletin concerning defective fuel pumps and; although he does not know the serial number of the pump that failed; the time period in which it was installed indicates that it was in fact one of the pumps covered by the service bulletin.

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Original NASA ASRS Text

Title: PA28 PLT LANDS WITH FUEL PRESSURE GAUGE VIBRATION. POSTFLT ANALYSIS REVEALS A RUPTURED FUEL PUMP DIAPHRAGM WHICH ALLOWED FUEL TO BE PUMPED INTO THE ENG OIL THROUGH THE ACCESSORY SECTION.

Narrative: AT ABOUT 6 MI OUT; APCHING DOWNWIND LEG; NOTICED THAT THE FUEL PRESSURE GAUGE WAS VIBRATING. IN THIS ACFT; THE FUEL PRESSURE HAD ALWAYS BEEN STEADY IN THE GREEN REGION. I WAS INTENDING TO LAND ANYWAY; SO CONTINUED THE APCH. WHEN THE ELECTRIC FUEL PUMP WAS TURNED ON; THE VIBRATION CONTINUED; BUT THE AVERAGE PRESSURE ROSE SLIGHTLY. IN THIS ACFT THE ELECTRIC FUEL PUMP HAD NEVER CAUSED THE FUEL GAUGE TO RISE OR TO MOVE IN ANY WAY. IN SUMMARY; 2 DIFFERENCES FROM NORMAL: A RAPID VIBRATION; AND A SLIGHT RISE WHEN THE ELECTRIC FUEL PUMP WAS TURNED ON ALONG WITH CONTINUED VIBRATION. AFTER LNDG; I ASKED THE LCL MECH TO COME AND LOOK AT THE INDICATIONS. HE CLBED INTO THE COCKPIT AND OBSERVED THE SYMPTOMS. THEN WE SHUT DOWN THE ENG AND ATTEMPTED A RESTART (WITH ELECTRIC FUEL PUMP OFF AS PER NORMAL PROC). AS THE ENG TURNED OVER ON STARTER PWR; THE FUEL PRESSURE WAS SEEN TO JUMP UP AND THEN FALL COMPLETELY TO ZERO IN RAPID SUCCESSION. THE MECH'S CONCLUSION (WHICH WAS CORRECT UPON DISASSEMBLY) WAS THAT ONE SIDE OF THE FUEL PUMP HAD FAILED AND THAT THE OTHER SIDE WAS PUMPING FUEL. WHAT WAS UNKNOWN FROM THE COCKPIT; HOWEVER; WAS THAT THE DIAPHRAGM BTWN THE FUEL SYS AND THE ACCESSORY BOX IN THE ENG HAD RUPTURED AND THAT FUEL WAS BEING PUMPED DIRECTLY INTO THE ACCESSORY SECTION. THE OIL TANK; WHICH HAD BEEN AT 7 QUARTS UPON TKOF 1 HR OR SO BEFORE AT TKOF; NOW CONTAINED 10 QUARTS OF HIGHLY DILUTED OIL. 2 OTHER FACTS: 1) I DO NOT KNOW EXACTLY HOW LONG THE GAUGE HAD BEEN VIBRATING BEFORE I NOTICED IT ABOUT 5 MINS BEFORE LNDG. 2) THE ACFT HAD HAD AN OIL CHANGE ONLY 2 FLT HRS BEFORE; YET THE MECH SAID THE OIL WAS VERY DIRTY ('AS DIRTY AS 50 HR OIL'); INDICATING THAT THE GASOLINE HAD ACTED AS A SOLVENT FOR ANY 'DIRTY' PARTS OF THE ENG. AT BEST; THE DILUTED OIL WAS NOT GOOD FOR THE ENG. I DO NOT KNOW THE EXTENT OF ANY FIRE HAZARD. I AM TOLD THAT IF THE FLT HAD CONTINUED; THE GASOLINE/OIL MIXTURE WOULD BE DRAINED OUT OF THE BREATHER TUBE UNDERNEATH THE ACFT. BUT IT WOULD BECOME MORE AND MORE DILUTED AS TIME PROGRESSED WITH POTENTIAL DAMAGE TO THE ENG; NOT TO MENTION THE EFFECT ON RANGE DUE TO THE LOSS OF THE FUEL. NO PLT THAT I HAVE TALKED TO HAD EVER REALIZED THE POTENTIAL DANGER OF A VIBRATING FUEL GAUGE. IF I HAD BEEN ON A XCOUNTRY; I WOULD HAVE CONTINUED TO DEST. I THINK MOST PLTS; WHO HAVE NOT HAD THIS EXPERIENCE; WOULD ALSO; WITH UNPREDICTABLE RESULTS. THE EXPERIENCED MECH SAID THAT IN HIS ENTIRE EXPERIENCE OF DECADES; THIS WAS THE SECOND FAILURE OF A FUEL PUMP. IN MY APPROX 7000 HRS; MUCH IN MULTIPLE ENGS; IT IS MY FIRST. THIS IS A RARE BUT POTENTIALLY DANGEROUS FAILURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE FUEL PUMP IN QUESTION WAS INSTALLED ON A LYCOMING IO-360 ENG. RPTR ADVISED THAT HE DID NOT NOTICE ANY DIFFERENCE IN ENG PERFORMANCE INFLT AND ALSO STATED THAT HIS ACFT DID NOT HAVE A CYLINDER HEAD TEMP GAUGE. RPTR STATES THAT HE RECENTLY LEARNED ABOUT A LYCOMING MANDATORY SVC BULLETIN CONCERNING DEFECTIVE FUEL PUMPS AND; ALTHOUGH HE DOES NOT KNOW THE SERIAL NUMBER OF THE PUMP THAT FAILED; THE TIME PERIOD IN WHICH IT WAS INSTALLED INDICATES THAT IT WAS IN FACT ONE OF THE PUMPS COVERED BY THE SVC BULLETIN.

Data retrieved from NASA's ASRS site as of January 2009 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.