ERA09LA490

The airplane was performing a training aerial application over a farm field when the engine lost power and the pilot performed a forced landing to a field, where the airplane impacted a tree. A subsequent examination of the engine revealed that within the accessory section, the idler gear assembly, which normally transferred power from the crankshaft to the left magneto and the camshaft, had been displaced. The short shaft had also been displaced. The mounting plate retaining screws appeared to be sheared. The crankcase surface area around the screw hole exhibited rotational scoring, and the idler gear, located in the oil sump, had no missing or damaged gear teeth. Metal particles were found in the bottom of the crankcase and oil sump. The engine operating time was below the recommended time between overhaul. The failure sequence could not be determined, and although the left magneto had been replaced approximately 12 flight hours prior, the replacement of the magneto could not be correlated to the displacement of the idler gear assembly.

On August 27, 2009, about 0900 eastern daylight time, a Piper PA-25-235, N7339Z, was substantially damaged when it impacted a tree after a forced landing near Decatur County Industrial Air Park (BGE), Bainbridge, GA. The private pilot sustained no injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local solo aerial application training flight. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The pilot reported that after completing a pre-flight inspection of the airplane he added "a few quarts of oil" to the engine. He confirmed the airplane was fueled and added water to the container on board for this training flight. After departure he flew to a pre-determined field to perform aerial application practice and empty the water only container on the field. After completion of that application he returned to BGE, refueled the airplane, filled the water container for another practice application, and taxied back out for departure. He reported that during the engine run-up he needed to lean the mixture a little, ran the engine at a lean fuel setting for a short period of time, went to the full rich mixture position and the engine "ran fine." After departing he flew to his pre-determined practice location and performed several passes along the field approximately 50 feet above ground level (agl). He stated that on the sixth or seventh pass across the field the "engine quit all of a sudden." He immediately landed in the field; however he was unable to stop the airplane prior to the trees that surrounded the field. He attempted to avoid as many trees as he could; however the left wing struck a tree approximately 9 inches in diameter damaging the wing. He stated that after recovery of the engine he was able to look at it himself and found no apparent external damage, the oil dipstick still had the proper amount of oil on it and had no metallic filings that he could see. He further reported that until the engine quit on him "everything was working at 100 percent." The owner of the airplane reported to the Safety Board that approximately 12 flight hours prior to the accident the left magneto had been replaced on the engine and that was the only mechanical work accomplished on it. The Federal Aviation Administration inspector that responded to the accident scene reported that there was substantial damage to the wing and that one propeller blade exhibited a slight aft bend and the other blade had no bending to it. During a follow-on examination the propeller was rotated by hand without restriction or binding and movement of all pistons was confirmed. Compression and valve movement was unable to be confirmed. The left magneto was removed and spark was produced on all towers when rotated by hand. The left magneto drive coupling was rotated by hand and was disconnected from the mating idler gear. The accessory drive housing was removed and rotational damage was observed nearthe idler gear associated with the left magneto and camshaft gear. The magneto drive gear and the camshaft gear teeth were damaged. Rotational scoring was observed on the crankcase were the idler gear attaches. The idler gear, short shaft, attachment plate, and two attachment bolts were separated. The idler gear and short shaft were located in the oil sump. The lower bolt end was located inside the engine case and the upper bolt end was sheared. The oil pan was drained and only small metal particulates were found. The attachment plate and the two bolt heads were not located. According to the airplane's engine logbook, the engine was overhauled on January 13, 2004. The most recent annual inspection was recorded on December 01, 2008 and at that time the airplane had 8,430.5 total hours in service and a recorded tachometer time of 1171.2 hours. The last recorded entry was on August 12, 2009 at which time the left magneto was replaced and at that time the recorded tachometer time was 1,370.4 hours and the time since major over haul was 1,286.4 hours. The 1300 recorded weather observation at BGE, included winds from 090 degrees at 3 knots, visibility 10 miles, clear skies, temperature 23 degrees C, dewpoint 22 degrees C, altimeter 30.04 inches of mercury.