Narrative:

After a successful precautionary landing due to a partial loss of engine power, examination of the engine revealed the cause of power loss. 2 of the spark plugs were lead-fouled to the point that they would no longer operate and all of the lower spark plugs in the engine had some degree of lead fouling on them. This fouling occurred very rapidly in flight after a normal engine run-up, and after only approximately 20 elapsed flight hours since the spark plugs were cleaned and svced. Lead fouling of aircraft spark plugs continues to be an everyday problem for all reciprocating aircraft engines, some engines appear to be more prone to fouling problems than others, but all engines will occasionally foul the spark plugs. In this observer's opinion the only real cure for this problem would be less lead in aviation gasoline, mainly 100 low lead fuel, because the manufacturers have tried various mechanical means to prevent this problem such as changing the design of spark plugs, etc, which have not been successful in preventing the lead fouling problem. The recency of spark plug cleaning and servicing seems to have little to do with plug fouling, as many times, plugs that have just been cleaned will foul out prior to the first run-up, less than 5 mins engine runt time. In closing, I do not have an answer for this problem, but it is one that continues to plague the reciprocating aircraft fleet and, at times, can become a hazard to flight operations. Perhaps it could be addressed at the industry-wide level to find a solution for an industry-wide problem.

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Original NASA ASRS Text

Title: FOULED PLUGS CAUSE PRECAUTIONARY LNDG.

Narrative: AFTER A SUCCESSFUL PRECAUTIONARY LNDG DUE TO A PARTIAL LOSS OF ENG PWR, EXAMINATION OF THE ENG REVEALED THE CAUSE OF PWR LOSS. 2 OF THE SPARK PLUGS WERE LEAD-FOULED TO THE POINT THAT THEY WOULD NO LONGER OPERATE AND ALL OF THE LOWER SPARK PLUGS IN THE ENG HAD SOME DEG OF LEAD FOULING ON THEM. THIS FOULING OCCURRED VERY RAPIDLY IN FLT AFTER A NORMAL ENG RUN-UP, AND AFTER ONLY APPROX 20 ELAPSED FLT HRS SINCE THE SPARK PLUGS WERE CLEANED AND SVCED. LEAD FOULING OF ACFT SPARK PLUGS CONTINUES TO BE AN EVERYDAY PROB FOR ALL RECIPROCATING ACFT ENGS, SOME ENGS APPEAR TO BE MORE PRONE TO FOULING PROBS THAN OTHERS, BUT ALL ENGS WILL OCCASIONALLY FOUL THE SPARK PLUGS. IN THIS OBSERVER'S OPINION THE ONLY REAL CURE FOR THIS PROB WOULD BE LESS LEAD IN AVIATION GASOLINE, MAINLY 100 LOW LEAD FUEL, BECAUSE THE MANUFACTURERS HAVE TRIED VARIOUS MECHANICAL MEANS TO PREVENT THIS PROB SUCH AS CHANGING THE DESIGN OF SPARK PLUGS, ETC, WHICH HAVE NOT BEEN SUCCESSFUL IN PREVENTING THE LEAD FOULING PROB. THE RECENCY OF SPARK PLUG CLEANING AND SVCING SEEMS TO HAVE LITTLE TO DO WITH PLUG FOULING, AS MANY TIMES, PLUGS THAT HAVE JUST BEEN CLEANED WILL FOUL OUT PRIOR TO THE FIRST RUN-UP, LESS THAN 5 MINS ENG RUNT TIME. IN CLOSING, I DO NOT HAVE AN ANSWER FOR THIS PROB, BUT IT IS ONE THAT CONTINUES TO PLAGUE THE RECIPROCATING ACFT FLEET AND, AT TIMES, CAN BECOME A HAZARD TO FLT OPS. PERHAPS IT COULD BE ADDRESSED AT THE INDUSTRY-WIDE LEVEL TO FIND A SOLUTION FOR AN INDUSTRY-WIDE 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.