HISTORY OF FLIGHT On November 21, 1996, about 1730 eastern standard time, a Cessna 172N, N4926G, operated by General Aviation Services Inc., was substantially damaged when it collided with trees during a forced landing near Andover, Massachusetts. The certificated commercial pilot and passenger were not injured. Visual meteorological conditions prevailed for the local flight. No flight plan was filed for the night flight that departed the Beverly Municipal Airport, Beverly, Massachusetts, about 1600. The aerial observation flight was conducted under 14 CFR Part 91. In a written statement submitted by the pilot, he stated that the purpose of the flight was to conduct a local traffic report. He performed a preflight inspection and then taxied to runway 34 for departure. Prior to takeoff, a satisfactory engine run-up was performed. About 1 hour and 10 minutes after takeoff, during cruise, at 1,500 feet above mean sea level, "the engine gave a loud "pop" or "bang" and lost 80 percent power, with some sputtering and backfiring." The pilot performed emergency procedures; however, the engine continued to lose power. He then performed a forced landing to an area of trees, and stated that "I slowed the aircraft down as much as possible and put it down on the tree tops. . . ." The accident occurred during the hours of darkness, about 42 degrees, 43 minutes north latitude, and 71 degrees, 20 minutes west longitude, at an elevation of 200 feet. PERSONNEL INFORMATION The pilot had a commercial pilot certificate with ratings for single and multiengine land, and instrument airplane. The pilot also held a flight instructor certificate with ratings for single and multiengine land, and instrument airplane. The pilot's most recent second class medical certificate was issued on August 13, 1996, with no limitations. The pilot reported that he had a total flight experience of 1,090 hours, of which 46 were at night. WRECKAGE AND IMPACT INFORMATION The airplane wreckage was examined at the accident site on November 22, 1996. On November 22, 1996, the wreckage was removed, and the engine was examined in a hangar, the following day, at the Lawrence Municipal Airport, North Andover, Massachusetts. Attempts to run the engine were unsuccessful; however, the propeller rotated. The engine was equipped with a Bendix D3000, single drive, dual magneto. Internal magneto timing was confirmed to be within limits. Attempts to confirm engine to magneto timing were unsuccessful. Rotation of the magneto failed to produce spark, and when removed, revealed that neither set of points would open; however, both sets of points opened with hand pressure. The magneto was disassembled, and when rotated by hand, the cam lobes did not contact either cam follower. Examination of the cam followers revealed that they were worn smoothly, at 45 degree angles. The cam followers appeared black in color at the edges of the 45 degree angle, and dark brown in the center. A review of the airplane's maintenance records revealed that a 100 hour inspection was performed on November 19, 1996, 2 flight hours prior to the accident flight. About 1 flight hour prior to the accident flight, the top spark plugs were removed and cleaned in response to a report that the magneto was misfiring. Also, on July 16, 1996, new points were installed in the magneto. ADDITIONAL INFORMATION The wreckage was released in part on November 23, 1996, to a representative of the insurance company, at Ryan Insurance Services, Inc., Scarborough, Maine. The magneto was retained for further examination and released on January 23, 1997.