On October 11, 2000, at 0614 eastern daylight time, an American Aviation AA-1A, N9394L, was substantially damaged during a forced landing after a loss of engine power, in Philadelphia, Pennsylvania. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the flight that originated at the Northeast Philadelphia Airport (PNE), at 0605. No flight plan was filed for the local aerial observation flight conducted under 14 CFR Part 91. In a written statement, the pilot reported that the purpose of the flight was "...routine traffic patrol of the Philadelphia area." He said that the airplane was in cruise flight at 1,200 feet mean sea level (msl), approximately 10 miles from the departure airport, when the engine began to run "rough". The pilot said he turned the airplane back towards PNE, and performed the procedures outlined in the owner's manual for a loss of engine power. He said the airplane continued to lose power and altitude as he continued towards the airport. According to the pilot: "Engine RPM was declining and I was unable to maintain altitude. I made smooth power adjustments with the throttle, but RPM's kept decreasing. I was in a slow descent, partial power, trimmed [at] best glide speed of 77 [knots]. I went back to both on the magnetos and continued with full rich mixture and fuel pumps on." The pilot said he was unable to reach PNE, and configured the airplane for an off-airport landing. He said he continued to evaluate and amend his landing sites due to obstructions, low light conditions, and vehicle traffic. He said: "As I approached the field, the engine made a loud popping noise and the propeller came to a stop. I turned the fuel pump off, mixture off, and throttle out. At my low altitude, I decided to put the airplane into a nearby field, into the wind, with full flaps. Once I had full flaps, I turned the master switch off. Unable to clearly see obstructions because it was dark out, I made a steep descent and slipped the airplane into a vacant field.... The airplane impacted a steel fence with the left outer wing hitting a tree." The pilot reported that there were no mechanical deficiencies with the airplane other than the loss of engine power. The airplane came to rest in an athletic field adjacent to a school, and was examined at the scene by a Federal Aviation Administration (FAA) aviation safety inspector. The inspector said the entire bottom of the airplane and the grass along the wreckage path were streaked with oil. The inspector said no oil registered on the engine oil dipstick. The airplane was removed from the site, and an engine inspection was performed on October 16, 2000. Removal of the engine cowling revealed no external damage to the engine. An oily residue was observed around the #2 exhaust pipe gasket and the #4 cylinder appeared discolored due to heat. The propeller was rotated by hand through an arc of approximately 120 degrees before the crankshaft locked. Removal of the #4 cylinder revealed a hole in the #4 piston at the 12 o'clock position beneath the piston ring lands. The hole carried through to the interior of the piston. Removal of the #2 cylinder revealed that the #1 connecting rod was separated from the crankshaft. The engine examination was suspended, and the engine was shipped to the Textron Lycoming Engine factory in Williamsport, Pennsylvania. Examination of the engine was completed under the supervision of an FAA inspector on December 14, 2000. Textron Lycoming issued a report on the engine exam, and the FAA inspector concurred with the report. The report was reviewed and discussed by telephone with the FAA inspector. According to the inspector, examination of the #1 and #2 cylinder assemblies revealed they were Superior cylinders. The #3 and #4 cylinder assemblies were reworked Lycoming cylinders. The individual piston part numbers could not be determined. Examination of the #1, #2, and #3 pistons revealed carbon deposits on top of the pistons. Examination of the #4 piston revealed no carbon deposits, and the hole that passed completely through the piston. In addition to the hole through the #4 piston, examination revealed a deep groove in the side of the piston in line with the forward piston pin plug. The plug was worn and heat damaged, with significant material loss. Material transfer in line with the piston plug was observed on the wall of the #4 cylinder. The #1 connecting rod bearing was deformed and impact damaged. The #2, #3, and #4 connecting rod bearings displayed smearing, streaking and heat damage. All of the crankshaft connecting rod journals displayed heat damage and scoring. The oil-scraper piston rings on the #1 and #2 pistons were installed backwards. The #3 cylinder had 3 base nuts installed upside down. Examination of the maintenance records revealed the owner/operator replaced the #3 and #4 cylinder assemblies on June 6, 2000, at 2,600 aircraft hours. He serviced the engine with 80 weight oil and returned the engine to service. On July 25, 2000, the #1 and #2 cylinder assemblies were replaced by a maintenance facility at 2,702 aircraft hours. The records revealed that the engine was then serviced with mineral oil as prescribed in the Lycoming Service Instruction 1427D. At the time of the accident, the airplane had accrued 2,937 hours. The pilot held a commercial pilot's certificate with ratings for airplane single engine land, multi-engine land, and instrument airplane. He reported 2,083 hours of flight experience, of which 1,630 hours were in the American AA-1A. The pilot reported 145 hours of flight experience in the AA-1A in the 90 days prior to the accident. Official sunrise on October 11, 2000, was at 0607 EDT. Weather at PNE, at 0554, was clear skies with 10 miles visibility. The winds were from 220 degrees at 7 knots.