ZILLAH, WA, USA
N1968H
BELL 47G-2
THE PILOT WAS MANEUVERING THE HELICOPTER ABOUT 50 FT AGL WHEN HE SUDDENLY LOST LATERAL CYCLIC CONTROL. THE HELICOPTER BEGAN TO ROLL LEFT DESPITE THE PILOT'S EFFORTS TO CORRECT. THE MAIN ROTOR BLADES CONTACTED TREES AND THE HELICOPTER CARTWHEELED INTO THE GROUND. EXAMINATION REVEALED THAT A PORTION OF THE LEFT CYCLIC CONTROL ROD HAD FAILED. FURTHER METALLURGICAL EXAMINATION SHOWED THAT THE FAILURE WAS DUE TO SEVERE CORROSION. AN EXAMINATION OF THE MAINTENANCE RECORDS REVEALED THAT THE HELICOPTER HAD NOT RECEIVED AN ANNUAL INSPECTION IN OVER TWO YEARS.
On June 23, 1995, about 1700 hours Pacific daylight time, N1968H, a Bell 47G-2 helicopter, operated by Heli Flight Ag Service, Inc., Zillah, Washington, impacted terrain during an uncontrolled descent and was substantially damaged in Zillah. The private pilot, the sole occupant, received serious injuries. Visual meteorological conditions prevailed and no flight plan had been filed. The aerial application flight departed from Buena, Washington, and was conducted under 14 CFR 137. According to the pilot: I pre-flighted, filled, and oiled 1968H in preparation for a survey flight. I took off from Buena and flew 2 miles Northeast of the airport where I landed to talk to a worker. I then returned to the idling helicopter and took off in a Northwestern direction. I started a turn to the South at an altitude of approximately 50 feet and a speed of 40 miles per hour when I lost lateral cyclic control. The aircraft continued to roll to the left while I attempted to correct it by moving the cyclic in the opposite direction. There was no feedback from the controls. The engine remained running. The throttle and collective control was normal. The rotor blades contacted some apple trees at a 90 degree angle and the aircraft cartwheeled on its top. A failed portion of the left lateral cyclic control rod was removed from the aircraft and sent to the Safety Board's Material's Laboratory Division. According to the Metallurgist's Factual Report (attached): The fracture location coincided with end of one of the rod end fitting inserts. Magnified examination of the fracture surfaces and surrounding area found severe corrosion on the interior of tube. The corrosion had significantly reduced the wall thickness of the tube at the fracture location. In some areas the wall had been reduced to a knife edge with no significant remaining thickness.... The remaining intact wall of the tube was fractured by overstress forces. Inspections within the tube uncovered extensive corrosion products on all of the interior surfaces and localized areas of deep pitting. The most severe corrosion appeared to be within two to three inches of the fractured end of the tube. According to an FAA aviation safety inspector from Renton, Washington, the helicopter had not received an annual inspection in over two years.
THE FAILURE OF COMPANY MAINTENANCE PERSONNEL TO PERFORM ADEQUATE INSPECTIONS OF THE HELICOPTER, AND THE FAILURE OF THE CYCLIC CONTROL ROD DUE TO CORROSION.
Source: NTSB Aviation Accident Database
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