HISTORY OF FLIGHT On October 19, 1999, about 0930 hours Pacific daylight time, a Cessna TR182, N756LE, made a forced landing 3 miles north of Fresno, California. The pilot declared an emergency due to smoke in the cockpit southeast of the Friant VOR while at 9,500 feet mean sea level. He shutdown the engine and landed on a road and collided with two parked cars. The pilot was not injured. The airplane was substantially damaged, and the cars received minor damage. The personal flight was being operated by the owner/pilot under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated at Cameron Park, California, at 0820, and was destined for Santa Ana, California. Postaccident examination of the exhaust system by a Federal Aviation Administration (FAA) inspector revealed a failure of the right heater core exhaust collector aft end plate. The end plate was found inside the cowling. Neither Cessna Service Bulletins nor FAA Airworthiness Directives addressed this potential failure. According to the Cessna model R182 and TR182 Service Manual: Exhaust System, section 11A-73, Inspection: "Since exhaust systems of this type are subject to burning, cracking and general deterioration from alternate temperature extremes and vibrations, inspection is important and should be accomplished every 50 hours of operation." According to the FAA inspector's telephone conversation with the maintenance technician, the inspection had been performed using the Cessna maintenance manual. A search of the FAA Service Difficulty Reporting System revealed three similar failures of the heater core assembly at 2,290, 2,223, and 1,762 total flight hours. According to records, the accident airplane heater core failure occurred about 1,313 hours since new. The last annual inspection occurred October 10, 1998, about 64 hours prior to the accident. About 52 hours prior to the accident, a presale inspection of the airplane and engine was accomplished at 1,261.8 hours. During the inspection a new ignition harness and new top spark plugs were installed. The carburetor was overhauled and a new spring was installed on the turbo waste gate. Airworthiness Directive 96-12-07 (Bendix, Impulse Coupling Inspection) was accomplished. The examination of the airplane and failed muffler revealed the absence of internal baffling to dissipate heat and reduce end plate erosion. Additionally, there was no deflector to preclude the impingement of hot gases onto the firewall or attached components such as the battery and the cabin heat valve. The muffler, Cessna part number 2254015-1, and end plate were sent to a materials laboratory for a metallurgical analysis of the failed material. According to design specifications provided by Cessna Aircraft Company, the material is 321 stainless steel per MIL-C-6721, and was 0.031-inch thick sheet. The accident end plate measured 0.015-inch thickness due to internal erosion. The laboratory report is attached.