NTSB Identification: LAX96FA080.
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Accident occurred Tuesday, December 26, 1995 in COMPTON, CA
Probable Cause Approval Date: 01/08/1997
Aircraft: Cessna 152, registration: N6110Q
Injuries: 2 Minor.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The instructor experienced a sudden reduction in engine rpm during climb out. After checking the engine and electrical systems, he took the controls and made a forced landing to a dry flood control canal. His attempts to advance the throttle resulted in a further loss of power. During the last portion of the approach he saw utility lines and attempted to avoid them but the aircraft struck an overhead cable. Witnesses heard popping sounds and saw smoke trailing the aircraft. An examination of the engine revealed a broken exhaust push rod. An examination found the push rod failed due to the manufacturing process in which it was artificially aged. This process made the push rod susceptible to stress corrosion cracking (SCC) with a lower stress threshold. The ASM handbook states that the preferred method is to maintain the material at the aging temperature for a longer period of time. The interference pins that are inserted in the ends of the push rod most likely produced hoop stress at a level sufficient to initiate SCC once the push rod is exposed to an environment of humid and/or salty air. SCC most likely began after manufacture, but before the push rod was placed into service during a period in which it was exposed to adverse environmental conditions.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: a push rod failed from fatigue as a result of longitudinal stress corrosion cracking. Full narrative available
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