On March 4, 1995, about 1615 hours Pacific standard time, a Boeing B75N1, N450SR, operated by the Stearman Flight Center of Chino, California, was substantially damaged during a forced landing near Gaviota, California. The forced landing was precipitated by a loss of engine power. The airplane was on a personal flight at the time of the accident and no flight plan was filed. There were no injuries to the ATP-rated pilot or his pilot rated passenger. The pilot reported that he had obtained a preflight weather briefing prior to departure. The flight was being conducted in visual meteorological conditions. The flight originated at Chino, California, on the day of the accident with a fuel stop at Santa Paula, California. The flight was destined for Santa Maria, California. The pilot stated that he suspected carburetor icing. The Santa Barbara airport is the nearest weather reporting facility and is located about 20 miles southeast of the accident site. At 1550, Santa Barbara was reporting a temperature of 59 degrees Fahrenheit with a dewpoint of 56 degrees Fahrenheit. While at Santa Paula, the pilots obtained a weather briefing from the Hawthorne Flight Service Station for Santa Barbara and Santa Maria, California. At the time of the briefing they were given the 1350 hour scheduled observation. Santa Barbara was reporting 2,500 scattered, and measured 4,700 overcast. About the time of the accident, the 1550 hour scheduled weather observation for Santa Barbara was reporting measured 800 feet overcast, 2 miles visibility, with light rain and fog. At the accident site a highway patrol officer reported the weather was 700 overcast, 1.5 miles visibility with mountain tops obscured. The pilot reported that he experienced carburetor icing and lost power. He crash-landed on a major highway median. Postaccident examination of the aircraft found an improper carburetor heat control with an unsecured housing, broken airbox with missing hardware (bolts), and a partially collapsed aluminum air intake duct to the airbox. In an attempt to determine the supplemental type certificate or field approval compliance for the carburetor control, records were obtained from FAA Oklahoma City. After several engine model changes, the last engine, a Pratt and Whitney R-985-14B, had been installed in the Sacramento, California, area. The modifier shop was no longer in business and the field approval information was not available. A mechanic who was familiar with the modification stated that the normal carburetor heat control had mechanical linkage, or an Ahrens control with a .090 core wire to move the cast aluminum airbox assembly.