BRISTOL, CT, USA
N6191M
Stinson 108-3
The pilot stated that he heard a loud noise accompanied by a loss of engine power. A forced landing was executed to a field. Inspection of the engine after the accident revealed two holes in the top of the engine crankcase. The number 3 piston, and it's connecting rod and bolts, were removed from the engine and examined. One of the connecting rod bolts contained microfissures typical of fatigue cracking on the head portion of the bolt. The fatigue cracking had initiated from multiple locations on one side of the underhead radius, and had propagated nearly all of the way through the cross section of the bolt before final separation. A review of the Airplane Engine logbooks revealed that the last Major overhaul was conducted on March 3, 1965.
On February 21, 1999, about 1158 Eastern Standard Time, a Stinson 108-3, N6191M, was substantially damaged when it impacted the ground during a forced landing near Bristol, Connecticut. The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot stated he had just terminated communications and radar services from the Bradley Windsor Locks TRACON, when he heard a loud noise accompanied by a loss of power. The pilot began a left-hand turn to search for a place to land. The pilot then transmitted to the radar controller that he was declaring an emergency and landing the airplane into a field. The field had an approximate length of 1,000 feet. As the airplane approached the field heading north, the pilot shut the engine down and was unable to slow the airspeed enough to make a landing at the beginning of the field. Approximately 400 feet from a tree line at the end of the field, the main wheels touched down and the pilot applied braking. Due to the excessive speed the airplane was light on it's wheels and the brakes were ineffective. The pilot attempted to turn to the left to avoid the tree line, but struck three small trees. The airplane came to rest in an upright position facing east. An inspection of the engine by the Federal Aviation Administration revealed two holes in the top of the engine crankcase. The engine was retained, and examined on March 12, 1999. The number 3 and 4 cylinders were damaged extensively, and removed from the crankcase. The Number 3 piston and connecting rod were found separated from the crankshaft. The connecting rod bolts were found in the oil sump pan. The number four piston and connecting rod remained connected to the crankshaft, and exhibited metal pinging on the piston skirt and rod. The connecting rod bolts were attached to the rod. The number 3 piston, and it's connecting rod and bolts, were forwarded to the National Transportation Safety Board Materials Laboratory, Washington, DC, for examination. According to the Metallurgist's Factual Report, one of the connecting rod bolts contained microfissures typical of fatigue cracking on the head portion of the bolt. The fatigue cracking initiated from multiple locations on one side of the underhead radius, and had propagated nearly all of the way through the cross section of the bolt before final separation. A review of the Airplane Engine logbooks revealed that the last Major overhaul was conducted on March 3, 1965, with a recorded total time of 1,612 hours. The pilot reported a total airframe time of 2,593 hours at the time of the accident.
The partial loss of power due to the failure of a fatigued connecting rod bolt.
Source: NTSB Aviation Accident Database
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