NTSB Identification: LAX91LA035.
The docket is stored on NTSB microfiche number 43989.
Accident occurred Tuesday, November 20, 1990 in FALLBROOK, CA
Probable Cause Approval Date: 12/30/1992
Aircraft: CESSNA 210M, registration: N9139M
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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 National Transportation Safety Board determines the probable cause(s) of this accident to be:

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.

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