CEN22LA106

The airplane’s engine lost partial power and the pilot was unable to maintain altitude. He executed a forced landing to a terraced farm field. During the landing, the airplane struck one of the terraced areas and nosed over. The airplane sustained substantial damage to the rudder, engine mounts, and lower right wing. Postaccident examination of the engine revealed that the ball end of the No. 2 cylinder exhaust valve rocker was not seated in the pushrod. Additionally, the head of one of the bolts securing the rocker arm bracket had fractured and the bolt head was found in the rocker cover. Based on the available evidence it is likely that the fractured bolt head allowed enough movement of the No. 2 cylinder rocker arm bracket for the pushrod to become separated from the ball end of the rocker arm. This prevented the exhaust valve for the No.2 cylinder from opening and thereby reducing the power output of the engine.

On January 23, 2022, about 1728 central standard time, a de Havilland Tiger Moth DH-82A, N5300, was substantially damaged when it was involved in an accident near Lampasas, Texas. The pilot and passenger received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that about 20 minutes into the pleasure flight the engine began to run rough, and he immediately turned the airplane back toward the departure airport, checked that the fuel was on, mixture was rich, and the throttle was open. The engine continued to lose power and he decided to divert to a different private airport. The engine was producing partial power but not enough to maintain altitude. As the airplane approached the private airport, the pilot perceived that the airplane was too high, and he turned the airplane. During the turn he realized that he had misjudged the height and decided that completing the turn was not a good idea, leveled the wings, and committed to going straight ahead. The area where the airplane landed was terraced and as it touched down the airplane hit one of the terraced areas, skipped, nosed over, and came to rest inverted. The airplane sustained substantial damage to the rudder, engine mounts, and lower right wing. After the accident, the pilot, who is also a mechanic, performed an examination of the airplane and engine. The engine was able to rotate, and compression was confirmed on all cylinders. While examining the valve system for the No. 2 cylinder he found that the ball end of the exhaust valve rocker arm was not seated in the end of the pushrod. He also found that one of the bolts securing the rocker arm assembly had the bolt head separated from its shank. The missing bolt head was in the rocker cover.