On December 17, 1996, at 1315 central standard time, a Cessna A188, N9860V, was substantially damaged during a forced landing near La Porte, Texas. The airplane, owned and operated by a private owner, was being operated under Title 14 CFR Part 91. The airline transport rated pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the business flight, for which a flight plan was not filed. The airplane departed from the La Porte Municipal Airport at 1130 on a local banner towing flight. The pilot told the FAA inspector that he had completed a banner towing flight around the city of Houston at approximately 1,000 feet AGL, and was in the process of entering the traffic pattern for runway 12 at the La Porte Airport. While at 800 feet MSL, the "the engine started to run rough, coughed and lost power." The pilot maneuvered the airplane towards a pasture while going through the engine restart checklist and dropping the banner. The engine surged a couple of times but did not regain power. The pilot elected to execute a forced landing to an open field, approximately 3 miles from the airport. The pilot stated that the airplane touched down in the three point attitude, and during the landing roll, the airplane impacted several small trees and went through a fence line. Examination of the airplane by an FAA inspector revealed that the rear spar on the right wing was bent, the left flap was torn, the left horizontal stabilator sustained structural damage, and both wing tips were damaged. The engine, serial number 566712, had accumulated a total of 2,659.4 hours, and 1,175 hours since the last overhaul. The reason for the loss of engine power could not be determined.