On September 5, 2022, about 1033 mountain daylight time, an Edward Long EZ, N444MR, was substantially damaged when it was involved in an accident near Medicine Bow, Wyoming. The pilot and passenger sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he and a passenger were on a cross-country flight from Kanab Municipal Airport (KKNB) Kanab, Utah, to Chadron Municipal Airport (KCDR), Chadron, Nebraska. While enroute, about 20 miles east of Rawlings, WY and about 7,500 ft msl, the airplane started to violently shake. The pilot initially maneuvered towards a local airport but decided to land the airplane on a highway. The airplane touched down hard, veered off the road, and impacted terrain. Subsequently, the airplane nosed over onto a fence and sustained substantial damage to the fuselage and wings (see Figure 1). Figure 1. View of airplane wreckage (courtesy of local law enforcement) A postaccident examination of the engine revealed oil and carbon buildup on the valve rockers, springs, and keys. It also revealed that the No. 4 engine exhaust valve head separated from its stem. The remaining valve stem had excessive play while situated in the valve guide (see Figure 2). Lycoming Service Bulletin No. 338C, Procedure to Determine Exhaust Valve and Guide Condition, was issued on November 22, 2004. It states: To insure positive and trouble free valve train operation, the inspection procedure described in this publication should be accomplished as recommended in the Time of Compliance section of this publication. Failure to comply with the provisions of this publication could result in engine failure due to excessive carbon build up between the valve guide and valve stem resulting in sticking valves or; broken exhaust valves which result from excessive wear (bell-mouthing) of the exhaust valve guide. This inspection was to occur every 400 hours, but no engine maintenance log entries documenting compliance with the Service Bulletin were found. No remnants of the No. 4 exhaust valve head were discovered within the cylinder or engine. The remaining exhaust valve stem measured approximately 3.5 inches in length, as opposed to the standard length of 4.3 inches. The face of the No. 4 piston and cylinder wall exhibited mechanical damage consistent with valve head separation. Figure 2. Five photos showing the No. 4 cylinder spring and rocker, piston, cylinder wall and exhaust valve seat. The recovered exhaust valve that fractured at the stem, rocker arm, inner and outer valve springs from the No. 4 cylinder were sent to the National Transportation Safety Board (NTSB) Materials Laboratory. The examination revealed that the fracture of the stem portion of the exhaust valve was the result of a fatigue crack that emanated from severe corrosion pits at the outer surface of the stem. The engine logbook entries revealed that Lycoming rebuilt the engine on November 24, 1981. No additional entries indicated that the engine had since been overhauled. The No. 1 cylinder was replaced on June 27, 2017. According to the Hobbs meter, the engine had accumulated a total of 898.1 hours. However, the engine's 41 years of service since its last overhaul exceeded the manufacturer's recommendations. According to Lycoming Service Instruction No. 1009BE, Time Between Overhaul (TBO) Schedules: All engine models are to be overhauled within twelve (12) calendar years of the date they first entered service or of last overhaul. This calendar year time period TBO is to mitigate engine deterioration that occurs with age, including corrosion of metallic components and degradation of non-metallic components such as gaskets, seals, flexible hoses and fuel pump diaphragms.