ONTARIO, CA, USA
N70PE
PIPER PA-31-350
THE PROPELLER SEPARATED FROM THE RIGHT ENGINE DURING THE INITIAL CLIMB. EXAMINATION OF THE WRECKAGE REVEALED THE PROPELLER HUB FRACTURE RESULTED IN ONE OF THE THREE PROPELLER BLADES DETACHING FROM THE HUB. THE REST OF THE PROPELLER HUB THEN SEPARATED STRIKING THE RIGHT FRONT OF THE FUSELAGE. OIL WAS SPREAD ACROSS THE AIRCRAFT NOSE AND WINDSHEILD. THE FUSELAGE RIGHT SIDE DAMAGE INCREASED AERODYNAMIC DRAG. WITNESSES REPORTED THE ENGINE COWLING WAS TORN. THE AIRCRAFT ENTERED A RIGHT TURN AND DIVE. IT IMPACTED THE GROUND IN A NEAR INVERTED ATTITUDE. METALLURGICAL EXAMINATION OF THE FAILED PROP HUB REVEALED METAL FATIGUE EMANATING FROM THE THREADED HOLE FOR THE GREASE FITTING. THE THREADS HAD BEEN DEFORMED BY SHOT PEENING, RESULTING IN INCREASED STRESS CONCENTRATIONS AT THE THREADS.
FAILURE OF THE RIGHT PROPELLER HUB DUE TO METAL FATIGUE WHICH RESULTED IN CATASTROPHIC SEPARATION OF THE PROPELLER. CONTRIBUTING TO THE ACCIDENT WAS DAMAGE DONE TO THE AIRCRAFT AIRFRAME IN FLIGHT BY THE SEPARATING PROPELLER MAKING THE AIRCRAFT UNCONTROLLABLE.
Source: NTSB Aviation Accident Database
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