LAX99LA108

The helicopter was in the process of finishing an aerial application run over an almond orchard when it collided with the ground in a nose down attitude. The pilot told the company owner and his family members that the flight controls 'went away' and he could not overpower the flight controls as the helicopter descended. The owner of the helicopter company stated that during the spray run the pilot flew up and over a powerline which was approximately 100 feet from the orchard. He reported that the pilot told him he heard a noise as he flew over the powerlines and then experienced the loss of control. Detailed examination and functional tests of various components of the helicopter's control systems failed to find any evidence of preimpact failure or malfunction. The tail stinger of the helicopter and an exemplar sample of the copper powerline wire was examined in a laboratory and it was determined that there was no wire transfer marks on the tail stinger. The pilot was transported to a hospital after the accident where tests later determined he had fractured his back. He died during a surgical procedure 2 days after the accident. The pilot held an airline transport certificate with over 32,000 hours of flight time, 28,000 of which were in helicopters.

History of flight

On February 21, 1999, at 1510 hours Pacific standard time, a Bell UH-1H helicopter, N6258Z, collided with the ground following a pilot report of an in-flight control system failure while conducting an aerial spraying operation near Glenn, California. The airline transport pilot was seriously injured during the accident sequence, and died in the hospital during a surgical procedure on February 23, 1999. The helicopter, owned and operated by Avag, Inc., was destroyed during the crash sequence. The aircraft was operating under 14 CFR Part 137 of the Federal Aviation Regulations when the accident occurred. The helicopter had departed a dirt-landing zone after being serviced with spraying chemicals moments before the crash. Visual meteorological conditions prevailed at the time and a flight plan was not filed for the flight.

The pilot told his son, who visited him in the hospital, that the helicopter kept banking in one direction and there was nothing he could do to stop it. He reported that his father said he lost control of the "systems" on the helicopter, that it was a mechanical failure of some sort, and that all of a sudden, the helicopter started veering to the right and as he tried to manipulate the controls, he was unable to change the direction of the helicopter's movement.

In his written report, the owner of the company reported that the pilot was just finishing a spray run on an almond orchard when the helicopter impacted the ground in a nose low attitude. He stated that there was a powerline approximately 5 to 8 tree rows (approximately 100 feet) in the orchard perpendicular to the path of flight. He stated that he thought the pilot flew up and over the powerline, and while descending back to the almond orchard the tail of the helicopter hit the powerline causing a tail high or nose low attitude. The pilot reportedly told him that after he went over the powerline, he heard a noise and lost control.

Personnel information

According to all sources of information, the pilot had accrued a total flight time in excess of 32,600 hours, with over 29,900 hours in various helicopters. A review of Federal Aviation Administration (FAA) airman records disclosed that he held an airline transport pilot certificate with a rotorcraft helicopter rating, and commercial pilot privileges in single engine land airplanes. The pilot held type ratings in the following helicopters: Sikorsky S-58, Sikorsky S-61, Sikorsky S-62, and the Boeing Vertol BV-44.

The owner of the company said that the pilot had not complained of any medical problems. He said that the pilot jogged regularly and was very health conscious. The owner said that he arrived at the crash site shortly after the crash and that the pilot was conscious and talking, complaining that his legs hurt.

Wreckage and impact

On February 24, 1999, at the request of Safety Board investigators, a technical representative from the Flight Safety Department of Bell Helicopter Textron, (BHT) traveled to Richvale, California, to examine the helicopter wreckage under the supervision of two inspectors from the FAA's Sacramento Flight Standards District Office. According to the BHT report, examination of the wreckage revealed that the main fuselage and tailboom were intact. Upward crushing and deformation were seen on the belly of the cabin, which was more severe on the right-hand side of the helicopter. Deformation was also present in the floor structure below the right front (pilot's) seat. The occupant restraints were intact and the right front seat did not exhibit evidence of deformation. The landing skids were separated from the fuselage, with overload fractures seen at the left rear, right rear, and left front crosstube/skid tube attachment fittings. The right side of the forward crosstube was fractured in overload outboard of the belly attachment fitting.

The tailboom was still attached to the fuselage and was relatively undamaged. A hole was observed in the left side of the tail rotor driveshaft cover on the fin, matching the dimensional geometry of the tailrotor blade. Examination of the tail stinger revealed a series of dark colored parallel lines, which were located on the left-hand underside of the stinger. According to BHT, these markings were present from several inches aft of the stinger's exit from the tailboom fairing all the way back to the aft end. The marks were described as approximately 1/2 inch in length and 1/8 inch apart.

The main transmission separated from the fuselage with overload fracture of the lower mounting flange of the transmission main case. The K-Flex main driveshaft was separated from the engine and transmission from overload fracturing of the load beams. The tail rotor driveshaft was intact and all the couplings and hanger bearings appeared to be in good condition. The tail rotor 42- and 90-degree gearboxes were intact and operable.

Control continuity was established from the cyclic, collective, and pedal controls in the cockpit to the hydraulic servos. The main rotor and tail rotor hydraulic servo actuators manually operated smoothly. The cyclic and collective boost tube extensions at the top of the servo actuators were fractured in overload at the riveted joints. The fluid lines from the pump to the servos, regulator, and filter modules were intact. The hydraulic reservoir had been broken loose from its mounting and a large hole had been punched in its left side.

The main rotor hub and control system was observed to be still attached to the mast, with the swashplate and sleeve assembly intact and operable. One of the scissors to equalizer link control tubes was fractured and the other was intact. Both swashplate drive links were separated from the swashplate due to fractures of the trunnion housings in the swashplate outer ring casting. The trunnions were still attached to the lower ends of the drive links. The scissors were intact and operable. The main rotor hub assembly was intact and the feathering and flapping axes moved freely. Additionally, it was noted that the stabilizer bar assembly was intact and operable.

Tests and research

The hydraulic pump was removed from the transmission by the FAA inspectors and was sent to the Safety Board's South Central Regional Office. On April 29, 1999, the pump was taken to BHT by a Safety Board investigator for testing. The hydraulic pump was set up on a bench test cell and run according to BHT standards. The pump operated at the following specifications: at 4,170 rpm and 900 psig (+100, -0) the flow standard was 6 gpm (+0, -1). The pump flow while running on the test stand was 5.75 gpm.

The outlet pressure standard was 1,000 psig (+ -25). The pressure was recorded at 1,050 psig. Additionally, a cavitation test was performed. No surging noise was heard and no air bubbles were observed in the flowrator. BHT concluded that the pump operated normally and no deviations from the acceptance criteria for new and overhauled pumps were observed which could have affected the pump's performance in the helicopter.

The three UH-1H hydraulic servo actuators were examined and bench tested at BHT under the supervision of a Safety Board investigator. Following an external examination, the actuators were installed in a flow bench and tested in accordance with Bell laboratory test procedure FW 211 Rev. R. The purpose of the test was to verify general functionality of the actuators. Installation of the units in the test bench required the installation of irreversible valves on the units. The bench test results presented in Table 1 of the attached BHT servo actuator report notes that each servo actuator operated smoothly in both the extend and retract direction. BHT concluded that the movement rates appeared normal. They did note, however, that the minimum operating pressure was exceeded and was likely due to the servo actuators being tested wit