On November 20, 1998, at 0830 central standard time, a Piper PA32-300 airplane, N2881U, owned and operated by the pilot, was substantially damaged during a forced landing following a loss of engine power near New Iberia, Louisiana. The non-instrument rated private pilot, who was the sole occupant, received minor injuries. Instrument meteorological conditions prevailed and a flight plan was not filed for the Title 14 CFR Part 91 personal flight. The flight originated from the Acadiana Regional Airport, New Iberia, Louisiana, at 0815, and was destined for New Orleans, Louisiana. During a telephone interview conducted by the NTSB investigator-in-charge (IIC), the pilot stated that he departed with a special VFR clearance and was climbing through 2,500 feet when he heard a "fairly loud explosion." The pilot stated that at first, he thought the engine noise sounded similar to a backfire. He noticed a power loss and turned back toward the Acadiana Regional Airport. A few minutes after the first explosion he heard a second "explosion that shook the airplane and sent a blanket of oil over the windshield." The pilot secured the engine and executed a forced landing to a field. During the landing roll, the aircraft crossed a road, impacted a tree with the left wing and the horizontal stabilizer, slid into a fence and came to a stop upright. An FAA inspector examined the airplane and reported that the right main landing gear, four feet of the left outboard wing, and the tip of the left horizontal stabilizer were separated from the airplane. The six seat, fixed landing gear airplane was powered by a Lycoming IO-540-K165 engine, S/N L-19502-48A. The airframe had accumulated a total of 3,392 hours at the time of the accident. The last annual inspection of the aircraft was completed on June 5, 1998. The last engine overhaul was completed on August 20, 1991. Since the last engine overhaul, the engine had accumulated 1,423.49 hours. Review of the maintenance records by the NTSB IIC did not reveal evidence of any uncorrected maintenance discrepancies. The Lycoming IO-540-K165 engine, S/N L-19502-48A, was inspected at the Textron Lycoming factory in Williamsport, Pennsylvania, under the supervision of an FAA inspector. Upon disassembly of the engine, the number 6 connecting rod was found fractured. After examining the connecting rod fracture surface, the failure was determined by the Lycoming metallurgist to be a "secondary failure resulting from overload." One of the number 6 connecting rod's bolt and nut assembly was then examined by the metallurgist. The nut was cut and split in the threaded area. Examination of the nut revealed that the first two threads, adjacent to the contact surface, were "stripped." Additionally, "no scuff marks were observed" on the copper plating in the undamaged portion of the nut contact surface. The metallurgist at the Lycoming factory determined that the two stripped threads indicated that the nut had backed off during operation of the engine, and that the lack of scuff marks on the contact surface copper plating indicated that the nut was not properly torqued during installation. See the enclosed metallurgist's report for details of the examination.