ERA19LA008

The pilot stated that, while en route to his destination, the airplane's engine sputtered and then lost total power. During the subsequent forced landing to a highway, the airplane landed hard, and the landing gear collapsed; the airplane sustained substantial damage to the fuselage. A postaccident examination of the engine revealed the No. 3 cylinder exhaust valve fractured where the stem transitioned to the valve head seat. The valve head impacted the No. 3 piston and became lodged between the crankcase and the camshaft, which resulted in the fracture of the camshaft. Fatigue cracking, which initiated at multiple sites, propagated through the valve stem. The presence of a tapered stem near the fracture surface, high temperature oxide deposits, and fatigue striations on the fracture surface suggested that the stem underwent spallation or erosion of the oxides formed during high temperature exposure, which would reduce the stem cross-section over time, increasing the likelihood of initiating fatigue cracking. Additionally, a localized area of wear on the top face of the valve stem was most likely due to the valve not rotating during operation, which could create hot spots or improper thermal dissipation in the hottest parts of the valve and lead to valve damage or failure.

On October 5, 2018, about 1445 central daylight time, a North American Navion A, N969TR, was substantially damaged during a forced landing near Stonewall, Mississippi. The private pilot was not injured. The airplane was registered to the pilot and was being operated as Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the flight that departed Key Field Airport (MEI), Meridian, Mississippi, at 1438, and was destined for Jack Edwards National Airport (JKA), Gulf Shores, Alabama.The pilot stated that he was flying at 3,500 ft when the engine sputtered. He informed air traffic control that he wanted to return to MEI and turned back toward the airport, but the engine stopped producing power. The pilot realized that he was not going to be able to reach MEI or any other airport and made a forced landing to a highway. The pilot said he bled off airspeed to avoid hitting cars and landed hard. The airplane's landing gear collapsed, and the airplane slid about 200 ft and came to rest upright on the road, which resulted in substantial damage to the fuselage. A postaccident examination of the engine revealed the No. 3 cylinder exhaust valve fractured where the stem transitioned to the valve head. The valve head was found lodged between the crankcase and the camshaft, and the camshaft was fractured between the No. 3 intake and exhaust lobes. Metallurgical examination of the liberated valve head and the valve stem revealed that the valve head was damaged from repeated contact with the piston and the valve stem exhibited fracture surfaces consistent with fatigue. The fatigue cracking propagated through the valve stem, initiating at multiple crack initiation sites on the stem surface. The valve stem also exhibited tapering near the fracture surface, and surface oxidation and deposits of lead-based compounds which were also present on the exterior of the stem adjacent to the fracture surface. A small depressed area was also noted on the top face of the valve stem, which was consistent with repeated contact with the adjacent rocker. The last annual inspection of the airplane and engine was on August 1, 2018. At the time of the accident, the engine had accrued a total of 1,705.0 hours and 641.5 hours since overhaul. Further review of the engine maintenance logbook revealed that on May 4, 2014, at an engine total time of 1,390.4 hours and 322.1 hours since overhaul, a mechanic "removed and reinstalled all six cylinders with new base seals, push rod tubes seals, intake tube seals, exhaust gaskets and rocker gaskets after resurfacing valves and seats."