Riverdale, CA, USA
N911PT
BELL OH-58C
The pilot was conducting agricultural spray operations when he experienced a flight control system anomaly that was described as a right rolling tendency. The pilot increased altitude in an effort to return to the operator's base for repairs. The helicopter became progressively difficult to control, continuing to roll right and not fully responding to left cyclic control inputs, and the pilot maneuvered to a nearby company loader to land. However, the right rolling tendency continued and the helicopter subsequently collided with terrain. Postaccident examination of the flight control assembly revealed that the gas producer throttle control cable, which is routed adjacent to the connecting linkage push-pull tubes, was entwined with the push-pull tubes. A section of the cable appeared to be pinched between the lower mixing lever unit and the tunnel partition wall. Multiple nylon loop cable clamps, used to secure the throttle cable to the vertical tunnel partition, were broken and separated; however, it was not possible to determine whether the observed damage was the result of the wreckage recovery efforts or a preexisting condition.
HISTORY OF FLIGHT On January 8, 2013, about 1225 Pacific standard time, a Bell OH-58 C helicopter, N911PT, collided with terrain near Riverdale, California. The commercial pilot, the sole occupant of the helicopter, sustained serious injuries. The helicopter sustained substantial damage to the forward fuselage, tail boom, and rotor assembly. The helicopter was registered to Blair Helicopter Services, Inc., and operated under the provisions of 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed and a company flight plan had been filed for the local aerial application flight. The pilot was conducting agricultural spray operations when he experienced a flight control system anomaly that was described as a lateral rolling tendency to the right. The pilot had just finished an application run when he experienced the anomaly and ascended in an effort to return to the operator's base of operation for repairs. The helicopter progressively became more difficult to control and the pilot diverted and maneuvered the helicopter to a nearby company loader to land. The helicopter continued to roll right and did not fully respond to left cyclic control inputs. The pilot continued to maneuver; however, the right rolling tendency continued and the helicopter subsequently collided with terrain. The operator reported that the helicopter impacted terrain in a right-side low attitude and bounced before it came to rest about 10-feet beyond the first identified point of contact with the ground. The pilot sustained serious injuries during the accident sequence and was transported to a nearby hospital. PERSONNEL INFORMATION The pilot, age 61, held a commercial pilot certificate with a helicopter rating and a second-class airman medical certificate issued December 28, 2012. The operator reported that the pilot's flying experience included 30,000 total flight hours, with 20,000 hours in helicopters and 3,000 hours in make and model. The pilot's most recent flight review was completed December 10, 2012. The pilot obtained most of his aerial application knowledge and experience through on-the-job training. The pilot had attended the Professional Aerial Applicators' Support System (PAASS) training provided by the National Agricultural Aviation Association in 2013. The pilot also held a chemical applicators license as required by the State of California. AIRCRAFT INFORMATION The helicopter (serial number 66-20356) was manufactured by Bell Helicopter in 1971 and delivered to the United States Army on December 27, 1971. It was retired from military service and issued a civilian Federal Aviation Administration (FAA) restricted category airworthiness certificate (type certificate number H22NM held by Arrow Falcon Exporters, Inc.) on November 24, 2008. Maintenance records indicated that the airframe total time, at conversion from military to civilian, was approximately 3,553 hours. The helicopter had accrued approximately 1,894 hours of service from the civilian certification date to the time of accident. Review of copies of maintenance logbook records showed an annual inspection was completed November 20, 2012, at an airframe total time of 5,426.1 hours, and engine total time of 5,059.7 hours. The airframe total time at the time of the accident was 5,443.8 hours. The helicopter was equipped with an IsoLair agricultural spray application system. The system incorporated a 130-gallon belly mounted fiberglass storage tank and a symmetrical spray boom assembly that spanned approximately 29 feet. TESTS AND RESEARCH Representatives from the National Transportation Safety Board, FAA, Arrow Falcon and the operator examined the recovered airframe, flight controls and associated hydraulic systems at the operator's hangar facility in Lemoore, California. The examination of the flight control assembly revealed that the gas producer throttle control cable (routed adjacent to the connecting linkage push-pull tubes) was entwined with the adjacent flight control push-pull tubes. A section of the cable appeared to be pinched between the lower mixing lever unit and tunnel partition wall. Multiple nylon loop cable clamps, used to secure the throttle cable to the vertical tunnel partition, were broken and separated. Two of the clamps were separated near the base of their associated machine screws. Another remained attached to its accompanying machine screw, however, the loop was fractured and the cable was no longer routed through the clamp. The gas producer throttle control cable's plastic outer sleeve showed signs of chafing and was exfoliated in a number of locations. The outer sleeve was dimpled and distorted in several locations throughout the length of the cable. Sections of the outer sleeve were bunched and crushed into pleated layers. Numerous sections of the cable showed gouge marks with areas of black discoloration. The protective sleeve was split in other locations which exposed the internal stainless cable. It was not determined if the before mentioned damage was the result of the wreckage recovery efforts following the accident or a preexisting condition. Subsequent to the airframe examination, representatives from NTSB, Bell Helicopter and Woodward HRT examined the main rotor flight control hydraulic actuators at Woodward's facilities in Santa Clarita, California. The left and right cyclic hydraulic actuators were installed on a bench test stand and functionally tested. Both actuators operated normally and no evidence of excessive external fluid leakage was noted. The collective hydraulic actuator sustained impact related damage and could not be functionally tested. An additional field examination report and flight control hydraulic actuators examination report are contained within the public docket. ADDITIONAL INFORMATION Maintenance records showed that an annual inspection of the airframe was completed November 20, 2012. The Inspection Guide published by the manufacturer established the required inspection schedule and inspection requirements for continued airworthiness of the helicopter. The following are excerpts from the Inspection Guide, Chapter 3, Section II: 2.13 - Inspect cyclic control for freedom of operation, boots and grips for condition and security of electrical connectors. 2.14.F - Inspect throttle control cable assembly for condition and security, (access center post).
A flight control malfunction while maneuvering for reasons that could not be determined because it was not possible to establish whether observed damage to the flight control assembly was the result of wreckage recovery efforts or a preexisting condition.
Source: NTSB Aviation Accident Database
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