Narrative:

While in cruise flight at 1500 ft MSL, en route from lee to X61 (bob white field, zellwood, fl), engine began to lose RPM. Student added throttle to maintain RPM, and correctly stated the problem. I took control of the aircraft, pulled carburetor heat on and added throttle to maintain RPM, while turning towards the selected possible landing site. Engine began to run rough, and lose RPM. Outside air temperature approximately 90 degrees F. Reducing RPM with throttle reduced roughness, but also power. Checked each magneto. Right magneto appeared to have failed completely, left magneto resulted in rough engine operations. Over the span of 1-2 mins the RPM steadily decreased until engine RPM was at idle/wind milling. Performed landing on a road in a public landfill (lake county landfill astatula). No damage to aircraft or property. No injuries. Fuel quantity was approximately 6-7 gallons (at least 1/2 full). After 1 hour of minor troubleshooting (checking fuel quantity, fuel filter, spark plugs, signs of damage, etc), engine restart was attempted to no avail. Magnetos were eiseman make, built in 1949, rebuilt in 1999. Suspect magneto coil material broke down under heat causing power loss. Magnetos had approximately 100 hours since rebuild. On discussing this occurrence with experienced mechanics, I found most felt this particular type of magneto was very unreliable and should not be in use. Recommend the eiseman magnetos be removed from aircraft to prevent future power losses. Callback conversation with reporter revealed the following information: the reporter stated the loss of power was caused by a broken rotor in the left magneto and the right magneto was intermittent due to a chafed 'P' lead rubbing on ground. The reporter said the reliability of the eiseman magnetos on this engine is poor and should be replaced with more reliable units.

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Original NASA ASRS Text

Title: A PIPER J-3D IN CRUISE AT 1500 FT MADE AN EMER LNDG DUE TO LOSS OF PWR CAUSED BY A FAILED L MAGNETO AND R MAGNETO CHAFFED 'P' LEAD.

Narrative: WHILE IN CRUISE FLT AT 1500 FT MSL, ENRTE FROM LEE TO X61 (BOB WHITE FIELD, ZELLWOOD, FL), ENG BEGAN TO LOSE RPM. STUDENT ADDED THROTTLE TO MAINTAIN RPM, AND CORRECTLY STATED THE PROB. I TOOK CTL OF THE ACFT, PULLED CARB HEAT ON AND ADDED THROTTLE TO MAINTAIN RPM, WHILE TURNING TOWARDS THE SELECTED POSSIBLE LNDG SITE. ENG BEGAN TO RUN ROUGH, AND LOSE RPM. OUTSIDE AIR TEMP APPROX 90 DEGS F. REDUCING RPM WITH THROTTLE REDUCED ROUGHNESS, BUT ALSO PWR. CHKED EACH MAGNETO. R MAGNETO APPEARED TO HAVE FAILED COMPLETELY, L MAGNETO RESULTED IN ROUGH ENG OPS. OVER THE SPAN OF 1-2 MINS THE RPM STEADILY DECREASED UNTIL ENG RPM WAS AT IDLE/WIND MILLING. PERFORMED LNDG ON A ROAD IN A PUBLIC LANDFILL (LAKE COUNTY LANDFILL ASTATULA). NO DAMAGE TO ACFT OR PROPERTY. NO INJURIES. FUEL QUANTITY WAS APPROX 6-7 GALLONS (AT LEAST 1/2 FULL). AFTER 1 HR OF MINOR TROUBLESHOOTING (CHKING FUEL QUANTITY, FUEL FILTER, SPARK PLUGS, SIGNS OF DAMAGE, ETC), ENG RESTART WAS ATTEMPTED TO NO AVAIL. MAGNETOS WERE EISEMAN MAKE, BUILT IN 1949, REBUILT IN 1999. SUSPECT MAGNETO COIL MATERIAL BROKE DOWN UNDER HEAT CAUSING PWR LOSS. MAGNETOS HAD APPROX 100 HRS SINCE REBUILD. ON DISCUSSING THIS OCCURRENCE WITH EXPERIENCED MECHS, I FOUND MOST FELT THIS PARTICULAR TYPE OF MAGNETO WAS VERY UNRELIABLE AND SHOULD NOT BE IN USE. RECOMMEND THE EISEMAN MAGNETOS BE REMOVED FROM ACFT TO PREVENT FUTURE PWR LOSSES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE LOSS OF PWR WAS CAUSED BY A BROKEN ROTOR IN THE L MAGNETO AND THE R MAGNETO WAS INTERMITTENT DUE TO A CHAFED 'P' LEAD RUBBING ON GND. THE RPTR SAID THE RELIABILITY OF THE EISEMAN MAGNETOS ON THIS ENG IS POOR AND SHOULD BE REPLACED WITH MORE RELIABLE UNITS.

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.