Narrative:

While cruising at an altitude of 2500 ft MSL on a clear VFR day, approximately 10-12 mi southeast of burbank airport, I became aware of rapidly increasing oil temperature. The electric oil pressure gauge began to show erratic values, ranging from a high of 75 psi to a low of 0 psi. The direct reading oil pressure gauge commenced a slow but steady decline stopping between the 50 psi and 75 psi markings (there are no intermediate markings). Normally this would read approximately 82 psi. Although the engine RPM remained steady, I also began to notice a hot and metallic odor as might reasonably be associated with an overheating engine. I proceeded to reduce power and to lower the nose of the aircraft so as to bring the temperature down both by decreasing combustion as well as increasing air flow. Additionally I began to plan for a possible emergency off airport landing. As the terrain in my immediate vicinity was not conducive to a successful emergency landing, I maintained the descent up to the area of the rose bowl sports arena. My reasoning was that if I had to land, the large parking lot would afford a good landing area. If however, it were occupied by motor vehicles, there was a golf course immediately to the east of the arena. As this proved to be the situation, I elected for a southwest landing on the golf course. By this time, I had reached an altitude of 1900 ft MSL on what I was planning to be a crosswind entry to the golf course 'traffic pattern.' at this time I simultaneously noticed 2 things. First the oil temperature and pressures were making their way back to normal levels, and the hot smell had disappeared. Secondly, I observed a police helicopter at my 1-2 O'clock position converging with me. Although I did not want to drift too far from the golf course, I had no choice but to make a slight turn away from the selected field in order to avoid a conflict with the other aircraft. I also decided to add power and gain some altitude (if the engine would take it). To my relief the engine responded normally and the temperature, although still slightly above normal, remained steady. The pressure now read 82 psi. I therefore elected to continue the flight and to climb to a more prudent altitude as long as the engine indications did not force me to do otherwise. To my consternation, I saw that the police helicopter was now closing on a 90 degree angle from my right. I made a slight left turn and proceeded to my destination of corona. The engine indications remained within tolerable limits for the remainder of the flight. Upon landing, I removed the engine cowling and discovered what appeared to be the remnants of a plastic bag wrapped around the top left bank of ignition wires. A portion of the bag had also been sucked down behind the rear most cylinder barrel and was blocking part of the engine oil heat exchanger unit. I suspect that during my descent the bag either shifted position or else was torn apart and thus allowed airflow to reach the heat exchanger and thus I was able to get the temperature of the oil back into tolerable limits. 3 days after this incident (oct/mon/97) I returned to inspect the aircraft and made an additional and somewhat surprising discovery, the oil cooler unit had imbedded in its corrugation, what appeared to be the desiccated husks of a dozen or more bees or wasps. What was doubly interesting was that they appeared to have died within the corrugations and not from the massive trauma normally associated with insect strikes. Could they have been attempting to live within the honeycomb structure? Doubtless the presence of so many foreign objects in the oil cooler added to the overheat problem.

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Original NASA ASRS Text

Title: PLT OF BIPLANE WAS MAKING AN APCH FOR A POSSIBLE OFF ARPT FORCED LNDG DUE TO LOW ENG OIL PRESSURE AND HIGHER THAN NORMAL ENG TEMP WHEN A GOV HELI FLEW NEARBY TO LOOK OVER THE RPTR. THE RPTR NOTICED THAT THE ENG'S INDICATIONS HAD RETURNED TO NORMAL SO A CLB AND TURN WAS INITIATED TO DEPART THE AREA.

Narrative: WHILE CRUISING AT AN ALT OF 2500 FT MSL ON A CLR VFR DAY, APPROX 10-12 MI SE OF BURBANK ARPT, I BECAME AWARE OF RAPIDLY INCREASING OIL TEMP. THE ELECTRIC OIL PRESSURE GAUGE BEGAN TO SHOW ERRATIC VALUES, RANGING FROM A HIGH OF 75 PSI TO A LOW OF 0 PSI. THE DIRECT READING OIL PRESSURE GAUGE COMMENCED A SLOW BUT STEADY DECLINE STOPPING BTWN THE 50 PSI AND 75 PSI MARKINGS (THERE ARE NO INTERMEDIATE MARKINGS). NORMALLY THIS WOULD READ APPROX 82 PSI. ALTHOUGH THE ENG RPM REMAINED STEADY, I ALSO BEGAN TO NOTICE A HOT AND METALLIC ODOR AS MIGHT REASONABLY BE ASSOCIATED WITH AN OVERHEATING ENG. I PROCEEDED TO REDUCE PWR AND TO LOWER THE NOSE OF THE ACFT SO AS TO BRING THE TEMP DOWN BOTH BY DECREASING COMBUSTION AS WELL AS INCREASING AIR FLOW. ADDITIONALLY I BEGAN TO PLAN FOR A POSSIBLE EMER OFF ARPT LNDG. AS THE TERRAIN IN MY IMMEDIATE VICINITY WAS NOT CONDUCIVE TO A SUCCESSFUL EMER LNDG, I MAINTAINED THE DSCNT UP TO THE AREA OF THE ROSE BOWL SPORTS ARENA. MY REASONING WAS THAT IF I HAD TO LAND, THE LARGE PARKING LOT WOULD AFFORD A GOOD LNDG AREA. IF HOWEVER, IT WERE OCCUPIED BY MOTOR VEHICLES, THERE WAS A GOLF COURSE IMMEDIATELY TO THE E OF THE ARENA. AS THIS PROVED TO BE THE SIT, I ELECTED FOR A SW LNDG ON THE GOLF COURSE. BY THIS TIME, I HAD REACHED AN ALT OF 1900 FT MSL ON WHAT I WAS PLANNING TO BE A XWIND ENTRY TO THE GOLF COURSE 'TFC PATTERN.' AT THIS TIME I SIMULTANEOUSLY NOTICED 2 THINGS. FIRST THE OIL TEMP AND PRESSURES WERE MAKING THEIR WAY BACK TO NORMAL LEVELS, AND THE HOT SMELL HAD DISAPPEARED. SECONDLY, I OBSERVED A POLICE HELI AT MY 1-2 O'CLOCK POS CONVERGING WITH ME. ALTHOUGH I DID NOT WANT TO DRIFT TOO FAR FROM THE GOLF COURSE, I HAD NO CHOICE BUT TO MAKE A SLIGHT TURN AWAY FROM THE SELECTED FIELD IN ORDER TO AVOID A CONFLICT WITH THE OTHER ACFT. I ALSO DECIDED TO ADD PWR AND GAIN SOME ALT (IF THE ENG WOULD TAKE IT). TO MY RELIEF THE ENG RESPONDED NORMALLY AND THE TEMP, ALTHOUGH STILL SLIGHTLY ABOVE NORMAL, REMAINED STEADY. THE PRESSURE NOW READ 82 PSI. I THEREFORE ELECTED TO CONTINUE THE FLT AND TO CLB TO A MORE PRUDENT ALT AS LONG AS THE ENG INDICATIONS DID NOT FORCE ME TO DO OTHERWISE. TO MY CONSTERNATION, I SAW THAT THE POLICE HELI WAS NOW CLOSING ON A 90 DEG ANGLE FROM MY R. I MADE A SLIGHT L TURN AND PROCEEDED TO MY DEST OF CORONA. THE ENG INDICATIONS REMAINED WITHIN TOLERABLE LIMITS FOR THE REMAINDER OF THE FLT. UPON LNDG, I REMOVED THE ENG COWLING AND DISCOVERED WHAT APPEARED TO BE THE REMNANTS OF A PLASTIC BAG WRAPPED AROUND THE TOP L BANK OF IGNITION WIRES. A PORTION OF THE BAG HAD ALSO BEEN SUCKED DOWN BEHIND THE REAR MOST CYLINDER BARREL AND WAS BLOCKING PART OF THE ENG OIL HEAT EXCHANGER UNIT. I SUSPECT THAT DURING MY DSCNT THE BAG EITHER SHIFTED POS OR ELSE WAS TORN APART AND THUS ALLOWED AIRFLOW TO REACH THE HEAT EXCHANGER AND THUS I WAS ABLE TO GET THE TEMP OF THE OIL BACK INTO TOLERABLE LIMITS. 3 DAYS AFTER THIS INCIDENT (OCT/MON/97) I RETURNED TO INSPECT THE ACFT AND MADE AN ADDITIONAL AND SOMEWHAT SURPRISING DISCOVERY, THE OIL COOLER UNIT HAD IMBEDDED IN ITS CORRUGATION, WHAT APPEARED TO BE THE DESICCATED HUSKS OF A DOZEN OR MORE BEES OR WASPS. WHAT WAS DOUBLY INTERESTING WAS THAT THEY APPEARED TO HAVE DIED WITHIN THE CORRUGATIONS AND NOT FROM THE MASSIVE TRAUMA NORMALLY ASSOCIATED WITH INSECT STRIKES. COULD THEY HAVE BEEN ATTEMPTING TO LIVE WITHIN THE HONEYCOMB STRUCTURE? DOUBTLESS THE PRESENCE OF SO MANY FOREIGN OBJECTS IN THE OIL COOLER ADDED TO THE OVERHEAT PROB.

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.