NTSB Identification: SEA98LA124.
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Accident occurred Tuesday, July 07, 1998 in ELTOPIA, WA
Probable Cause Approval Date: 01/10/2000
Aircraft: Hiller UH-12E, registration: N5360V
Injuries: 1 Minor.
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 reported that he had just taken off to the south. About 30 seconds into the flight, a control paddle departed the helicopter, and control was lost. The helicopter crashed in a cornfield and rolled inverted, after which the pilot exited. Post-crash examination revealed that a flight control rotor blade departed the helicopter. The spar from the blade separated from a fatigue crack, which originated near one of the outboard retention bolt holes and propagated nearly all of the way around the spar on both sides. The NTSB materials laboratory determined that the fatigue cracking initiated from corrosion pitting. FAA Airworthiness Directives in effect at the time of the accident required inspection of the spar tube, cuff, and bolt holes every 100 hours to detect corrosion and cracking in accordance with a Hiller service bulletin. This service bulletin required a visual inspection for corrosion of the inside surface of the cuff and the inner and outer surfaces of the spar tube. This visual inspection was to be followed by a dye-penetrant inspection of the spar and the cuff to detect any cracks. Although logbook entries (of less than four months and 70 hours time in service before the accident) cited compliance with the relevant AD and service bulletin, no evidence was found of dye penetrant residue, zinc chromate primer, or the required sealant material during NTSB materials laboratory testing.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Fatigue of the control rotor blade spar and failure of the maintenance inspector to follow the procedures set forth in the airworthiness directive. Full narrative available
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