Event Description
While returning to the airport during initial descent, the engine began to run rough and lose power. The roughness improved momentarily, followed by severe engine vibration, a loud bang, and complete loss of engine power. During a forced landing in a densely populated neighborhood, the airplane struck a power line, veered to the right, collided with the street, and came to rest in the front yard of a daycare center.
Flight Crew
The first pilot, a certificated flight instructor, was providing flight instruction to the second pilot, a certificated private pilot.
Engine Examination
Examination of the engine revealed that the number 3 cylinder was broken free at the crankcase-mounting flange. A metallurgical examination of the number 4 position crankcase thru-bolt showed signs of fatigue cracking that emanated from the thread root. In addition, the cylinder flange mating surface displayed signs of fretting damage consistent with relative movement between the cylinder and the crankcase.
Maintenance History
The operator's director of maintenance stated that about 40 hours before the accident, he repaired a substantial oil leak between the number 3 cylinder and the engine crankcase. He said that during the repair he removed the number 4 position crankcase thru-bolt nut, applied an engine sealant, reinstalled the through bolt nut, and torqued the nut in accordance with the Lycoming overhaul manual. There was no engine log book entry pertaining to the engine total time, aircraft total time, or date when this repair was accomplished.