NTSB Identification: LAX95LA096.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Accident occurred Friday, February 03, 1995 in CHOWCHILLA, CA
Probable Cause Approval Date: 08/31/1995
Aircraft: HILLER UH-12E, registration: N9293Z
Injuries: 1 Uninjured.

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

THE PILOT WAS APPLYING CHEMICALS TO A FIELD AT A SLOW AIRSPEED ABOUT 10 FEET OFF THE GROUND. A SEVERE VIBRATION STARTED THROUGH THE AIRFRAME, AND THE PILOT DECIDED TO LAND IMMEDIATELY. THE PILOT WAS TURNING TO A LANDING AREA WHEN THE VIBRATION SUDDENLY CEASED, THE HELICOPTER FELL TO THE GROUND ON ITS NOSE, AND ROLLED OVER ONTO ITS TOP. ONE MAIN ROTOR BLADE AND HALF THE HUB WERE FOUND MORE THAN 100 YARDS FROM THE HELICOPTER. THE SECOND BLADE WAS FOUND ATTACHED TO THE REMAINDER OF THE HUB, ABOUT 150 FEET FROM THE WRECKAGE. THE TWO PIECES OF THE FRACTURED AND SEPARATED MAIN ROTOR HUB WERE RECOVERED AND METALLURGICALLY EXAMINED. THE HUB SEPARATED DUE TO A FRACTURE THROUGH ITS CENTER. THE EXAMINATIONS DISCLOSED THAT THE FRACTURE THROUGH THE HUB CENTER STEMMED FROM FATIGUE CRACKS WHICH INITIATED FROM THE TENSION-TORSION PIN HOLE ON THE LEADING EDGE SIDE OF ONE HUB ARM. THE ORIGIN POINT OF THE FATIGUE CRACK WAS DETERMINED TO BE INSIDE THE TT PIN HOLE AND EXHIBITED CORROSION DEPOSITS TYPICALLY SEEN IN ALUMINUM ALLOYS. THE CRACK WOULD NOT HAVE BEEN VISIBLE DURING AN EXTERNAL INSPECTION. THE FATIGUE CRACK AND FRACTURE ARE IN AREAS NOT COVERED BY THE RECURRING INSPECTION REQUIREMENTS OF AD 73-20-03.

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

the in-flight failure and separation of the main rotor hub due to a fatigue crack.

Full narrative available

Index for Feb1995 | Index of months