NTSB Identification: ATL89DKG06.
The docket is stored on NTSB microfiche number 41097.
Accident occurred Friday, September 29, 1989 in PLAINS, GA
Probable Cause Approval Date: 06/30/1992
Aircraft: BELL UH-1B, registration: N840MC
Injuries: 2 Fatal.

DURING A POSITIONING FLT, AN IN-FLIGHT BREAKUP OF THE HELICOPTER OCCURRED IN THE VICINITY OF WHERE IT WAS CROSSING A LINE OF TREES BETWEEN 2 CLEARED AREAS. WRECKAGE WAS FOUND SCATTERED OVER AN AREA OF APRX 300 YDS IN LENGTH, ALONG A HEADING OF 340 DEG. AT THE SE END, PIECES WERE FOUND FROM THE LEFT SPRAY BOOM & MAIN ROTOR AERODYNAMIC FAIRING. FURTHER TO THE NW, VARIOUS PARTS WERE FOUND FROM THE LEFT SIDE OF THE HELICOPTER, LEFT SPRAY BOOM & TAIL ROTOR. THE MAIN ROTOR & MAIN ROTOR HUB WERE FOUND ABOUT 120 YDS TO THE RIGHT OF THE WRECKAGE PATH. THE FUSELAGE, ENG & TRANS- MISSION WERE FOUND ABOUT 240 YDS NW OF THE 1ST PART OF THE WRECKAGE. AN EXAM OF THE WRECKAGE REVEALED THE MAIN ROTOR SYSTEM HAD SEPARATED DUE TO MAST BUMPING. THERE WAS EVIDENCE THE LEFT SPRAY BOOM HAD CONTACTED THE MAIN ROTOR BLADES DURING FLT. ALL OF THE FRACTURES OF THE SPRAY BOOM, STEEL TRUSS & ASSOC LUGS INDCD OVERLOAD FAILURE IN AFT & UPWARD DRCTN. THE SPRAY ASSEMBLY & BOOM HAD NOT BEEN INSTALLED IN ACCORDANCE WITH FAR PART 23.

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

IMPROPER MODIFICATION OF THE HELICOPTER BY THE COMPANY/OPERATOR, AND FAILURE OF THE SPRAY BOOM, WHICH RESULTED IN MAST BUMPING, AND SUBSEQUENT FAILURE OF THE MAIN ROTOR ASSEMBLY.

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