HERKIMER, NY, USA
N2113U
Brantly Helicopter B-2
THE AIRCRAFT WAS FOUND IN A WOODED AREA ABOUT 1-1/2 MILES NORTH OF THE DEPARTURE HELIPORT. ON-SCENE INVESTIGATION REVEALED A HOLE IN THE ENGINE CASE NEAR CYLINDER #4. A LATER ENGINE TEARDOWN SHOWED THAT THE #4 CONNECTING ROD HAD FAILED AT THE CRANKSHAFT JOURNAL. THE JOURNAL DISPLAYED TYPICAL DISCOLORATION AND SCORING FROM OVERHEATING AND A LACK OF LUBRICATION. THE OIL PRESSURE RELIEF VALVE SPRING, P/N 68668, WAS BROKEN INTO 3 PIECES. METALLURGICAL EXAM REVEALED THAT THE SPRING FAILED IN FATIGUE WHICH PROBABLY ORIGINATED FROM PRE-EXISTING CRACKS DEVELOPED AS A RESULT OF HYDROGEN EMBRITTLEMENT. THE GENERAL CONDITION OF THE CADMIUM PLATING ON THE SPRING WAS VERY POOR, AND PLATING IS NOT CALLED OUT IN THE ENGINEERING DRAWING.
A FORCED LANDING IN UNSUITABLE TERRAIN DUE TO AN INTERNAL ENGINE FAILURE. THE ENGINE FAILURE SEQUENCE WAS INITIATED BY A FAILED OIL PRESSURE RELIEF SPRING WHICH HAD FAILED IN FATIGUE DUE TO IMPROPER PLATING OF THE SPRING. THE SPRING FAILURE CAUSED OIL STARVATION TO THE ENGINE CRANKSHAFT AND RESULTING FAILURE OF A CONNECTING ROD.
Source: NTSB Aviation Accident Database
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