Aircraft: Beech Bonanza. Injuries: 3 Fatal. Location: Daggett, Calif. Aircraft damage: Destroyed.
What reportedly happened: While in cruise flight, the pilot transmitted that he was in trouble because the airplane had experienced a propeller failure. The air traffic controller provided him with instructions to the nearest airport, which was about 21 miles away. The pilot radioed that he thought that he could make it and began a descent toward the airport.
A witness near the accident site saw the airplane flying in a southwesterly direction about 500 feet AGL. As the airplane approached a set of suspended power lines, it pitched up 15°, increased altitude by 100 to 200 feet, yawed to the right, made two 360° turns, then hit the ground.
A post-accident examination of the engine revealed a 2-inch hole in the top of the crankcase between the Nos. 3 and 4 cylinders. The No. 1 piston connecting rod had separated from the crankshaft, bending the end cap flat.
Laboratory examination of the bearing identified circumferential wear marks on the back side of the bearing insert. The wear marks on the backside of the intact insert, the lack of heat damage to the connecting rod journal, and the lack of heat damage to the connecting rod and end cap suggest that the bearing began to spin, which led to extrusion/ejection of half of the connecting rod bearing. Once the bearing was free, fragments of bearing material worked their way up between the piston and the cylinder wall, causing damage to and embedding in the piston skirt. The increased clearances between the connecting rod end cap and connecting rod journal caused stress, resulting in a fatigue fracture of the connecting rod bolts.
During the investigation it was discovered that in 1998, after 1,002 hours of operation, the engine was top overhauled. A top overhaul does not inspect or replace items inside the crankcase, such as the main bearings or connecting rod bearings. At the time of the accident, the engine had accumulated 2,601 hours. The engine manufacturer recommends that time between overhaul be 1,500 hours or every 12 years.
Probable cause: A loss of engine power due to the separation of a connecting rod, and the pilot’s failure to maintain control during a sudden maneuver to avoid power lines during the descent, which resulted in an unrecoverable aerodynamic stall and subsequent spin. Contributing to the accident was noncompliance with the manufacturer-recommended engine overhaul schedule.
NTSB Identification: WPR12FA012
This October 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.