FALLBROOK, CA, USA
N9139M
CESSNA 210M
A CESSNA 210M LOST ENG POWER AND COLLIDED WITH A POLE AFTER A FORCED LANDING ON A CITY STREET. THE ENGINE CRANKCASE WAS FRACTURED AND THE #5 PISTON CONNECTING ROD HAD SEPARATED FROM THE ENG AND WAS FOUND ALONG THE WRECKAGE PATH. EXAM OF THE NUMBER 5 CYLINDER WALL DISCLOSED EVIDENCE OF THE AREA BELOW THE NORMAL PISTON STROKE BEING SCRAPED BY THE PISTON RINGS. ACCORDING TO THE METALLURGIC REPORT, THE PISTON'S CONNECTING ROD FAILED DUE TO A FATIGUE CRACK. THE CONNECTING ROD WAS BENT SOME TIME AFTER INITIAL ENG OPERATION. THE BENDING THAT OCCURRED TO THE NO. 5 CONNECTING ROD IS CHARACTERISTIC OF AN HYD LOCK CONDITION WHERE THE PISTON IS FORCED AGAINST INCOMPRESSIBLE FLUIDS BETWEEN THE PISTON AND CYLINDER HEAD. NO INDICATION OF METALLURGICAL DEFECT WAS OBSERVED IN THE CONNECTING ROD. HARDNESS READINGS ON THE CONNECTING ROD, WHICH INDICATES THE STRENGTH, CONFORMED TO MATERIAL SPECIFICATIONS. THE MAINTENANCE RECORDS NOTE THAT A MAJOR OVERHAUL WAS ACCOMPLISHED 207.8 HOURS BEFORE THE ACCIDENT.
THE FAILURE OF THE NUMBER 5 CYLINDER PISTON CONNECTING ROD DUE TO BENDING AND SUBSEQUENT FATIGUE FRACTURE. CONTRIBUTING TO THE ACCIDENT WAS THE IMPROPER STARTING PROCEDURE ACCOMPLISHED BY AN UNIDENTIFIED PERSON WHICH RESULTED IN EXCESSIVE FUEL IN THE CYLINDER RESULTING IN A HYDRAULIC LOCK WITHIN THE NUMBER 5 CYLINDER.
Source: NTSB Aviation Accident Database
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