Los Olivos, CA, USA
N44094
Aviation International Rotors CH-54A
The pilot was preparing to takeoff in furtherance of a contract firefighting flight for the California Department of Forestry & Fire Protection (CAL FIRE). The helicopter was on the ground with its engines at operational power, when a mechanical malfunction occurred. The pilot was unable to maintain roll control, and the helicopter initiated an uncommanded slow rollover onto its side. The helicopter was operated and maintained by its owner pursuant to a specific maintenance program. A component of this program involved examining each main rotor servo mount pin for rust and corrosion, and performance of dimensional checks prior to reinstallation of the inspected components. The company mechanic reported that he completed the inspection and found no faults. The records reflect that the components were reassembled and installed on the helicopter that was then returned to service. The accident occurred about 8 operational hours and 2 days following the reported maintenance inspection. During the accident investigation, components that secured one of the three main rotor blade pitch change servo units to the helicopter were found a few yards away from the main wreckage. The components consisted of a nut, bolt, pin, and plate. The components had secured one of the servo units to the helicopter transmission on one end and the helicopter swash plate on the other end. Separation of these components from the helicopter resulted in separation of the servo unit, and consequently resulted in a loss of main rotor blade pitch control. Upon the subsequent visual examination of components, evidence of severe wear and corrosion was detected inside of the nut holding down the retainer mounting strap, which indicates that this area had not been inspected for some time. Once the main rotor servo cylinder and transmission attaching lug separated, the rotor system would travel to the full pitch position, thereby resulting in the helicopter experiencing an uncommanded lift and roll to the right.
HISTORY OF FLIGHT On July 8, 2007, about 1608 Pacific daylight time, an Aviation International Rotors CH-54A, N44094, experienced a mechanical malfunction and rolled over during takeoff from the Figueroa Helibase about 4 miles north of Los Olivos, California. The helicopter was owned and operated by Heavy Lift Helicopters, Inc., Apple Valley, California, under a "call when needed" contract for the California Department of Forestry & Fire Protection (CAL FIRE). The purpose of the flight was to support CAL FIRE's wildland fire suppression activities of dispersing retardant on a fire in Santa Barbara County, California. Visual meteorological conditions prevailed, and a company flight plan had been filed. The helicopter, which was operating in the restricted category, was substantially damaged when the main rotor blades impacted the ground. The blades were broken, the cockpit was deformed, and the fuselage was broken and partially detached just behind the cockpit. The airline transport certificated pilot and the commercial certificated copilot sustained minor injuries. The flight was performed under the provisions of 14 Code of Federal Regulations Part 133 (rotorcraft, external load), and it was originating at the time of the accident. The pilot reported that while the helicopter was on the ground and at operating power, an event occurred that resulted in his losing control of the helicopter. The helicopter experienced an uncommanded slow rollover to the right. HELICOPTER MAINTENANCE PROGRAM The helicopter was maintained by company personnel on a Federal Aviation Administration (FAA) approved inspection program. The last (Phase 4) inspection was performed on July 6, 2007, at a total time of 8,457.1 hours, as indicated in the operator's "Flight and Maintenance Log." The FAA approved form for the Phase 4 inspection lists the specific work to be accomplished during the phase inspection. Item number 12 on the inspection form states the following must be examined during the Phase 4 inspection: "Each main rotor servo mount pin for rust and corrosion (remove, service, check minimum dimension and reinstall.)" In follow up to item number 12, the mechanic is required to record on the form his observations and actions to fulfill the specific inspection requirements. The post accident examination of this form revealed the following remark: "No Faults Found." Also, regarding the action taken, the form was marked: "Insp OK." Following completion of the Phase 4 inspection the helicopter was returned to service. The accident occurred 2 days later at an approximate total helicopter time of 8,465 hours. WRECKAGE AND IMPACT INFORMATION The FAA coordinator and representatives from CAL FIRE examined the helicopter on scene. The FAA coordinator reported to the National Transportation Safety Board investigator that components, which secure one of the three main rotor blade pitch change servo units to the helicopter, were found a few yards away from the main wreckage. The components consisted of a nut, bolt, pin, and plate. The components secured one of the servo units to the helicopter transmission on one end and the helicopter swash plate on the other end. The FAA coordinator opined that the integrity of this assembly is critical to flight safety. Separation of these components from the helicopter will result in separation of the servo unit, and consequently in a loss of main rotor blade pitch control. The loss of control would likely manifest itself in a rollover event if the helicopter were in the process of taking off, or a loss of flight control if the event were to occur while airborne. CAL FIRE personnel made the following (summarized) statements regarding its findings: The evidence indicates that the Phase 4 inspection, item number 12, was signed off as completed; however, evidence indicates that this procedure was not complied with. Observed evidence of severe wear and corrosion inside of the nut holding down the retainer mounting strap would indicate that this area had not been satisfactorily inspected for some time. CAL FIRE personnel opined that during the accident sequence, a mechanical malfunction occurred that related to the retainer pin becoming lose and separating from the main rotor servo cylinder and transmission attaching lug. This action permitted the rotor system to travel to the full pitch position, thereby resulting in the helicopter experiencing an uncommanded lift and roll to the right.
The company mechanic's inadequately performed maintenance and inspection, which resulted in a flight control malfunction and loss of control during takeoff.
Source: NTSB Aviation Accident Database
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