Incident Overview
During the takeoff initial climb, the airplane lost engine power and collided with vehicles during a forced landing on a freeway. The aircraft was largely consumed by a post-impact fire.
Maintenance History
Earlier, during a cross-country flight, the engine began running rough, prompting the pilot to divert to Concord. The pilot contacted the fixed-base operator (FBO) from which the airplane was rented. The FBO was informed of the problem and subsequently contacted a maintenance facility at Concord. That facility found a broken exhaust valve in the number 2 cylinder and estimated the repair at 20 labor hours. The rental company declined to use them and dispatched its own mechanic to Concord.
Repair and Departure
The company mechanic replaced the number 2 cylinder and piston. However, the replacement piston was an incorrect high-compression piston instead of the correct low-compression piston. The mechanic completed the work in three hours and did not conduct a complete inspection of the engine for missing pieces of the exhaust valve. After verbally telling the pilot the airplane was "good to go," the pilot fueled the airplane to capacity and performed an engine run-up, noting no abnormalities. He then departed using runway 19L, the shortest runway at Concord-Buchanan Field (CCR).
Engine Failure and Forced Landing
When the airplane reached an altitude of approximately 150 to 200 feet above ground level, the pilot noted a loss of engine power. Determining that a return to the airport was not possible, he elected to land on the I-680 freeway. During the landing, the airplane collided with vehicles and came to rest in the center divider.
Post-Accident Examination
Examination of the engine revealed several issues. Cylinders 2, 4, and 6 showed mechanical damage from a foreign object, most likely the number 2 exhaust valve head. The number 4 cylinder contained a portion of the number 2 valve head. Spark plugs in cylinders 2, 4, and 6 were mechanically damaged with electrode gaps closed or nearly closed. Cylinders 1, 2, 4, 5, and 6 contained improper pistons certified for IO-360 series engines, not for the accident engine, a TSIO-360-FB. The turbocharger turbine wheel exhibited foreign object damage. The number 2 main bearing was rotated 90 degrees. Bearing rotation and fretting damage to the number 2 and 3 upper main bearing supports and backbone bolt locations 6 through 11 indicated that the through bolts were inadequately torqued during installation of the number 2 cylinder.