ANAHUAC, TX, USA
N59396
Bell 206B2
The helicopter was being used to perform sling load operations, transporting water in a 100 gallon bambi bucket suspended by a 100 foot long line. During the operation, the helicopter impacted in a marshy area at a high rate of descent with very low forward speed approximately 100 feet west of his water pick up point. There were no reported eyewitnesses to the accident. A ground impression (corresponding to the water bucket) was found approximately 200 feet to the west of the resting place of the main wreckage. The 3 to 5 foot tall grass on the southern portion of the hole made by the water bucket was found pushed or laid back in a southerly direction. Deep impressions were found aft of the toe of the left skid tube (at the attaching point where it attaches to the crosstube), which corresponded to the steel cable that was being used in conjunction with the external load. No similar impressions were found on the other skid or crosstube assemblies. No evidence of pre-impact mechanical failure or malfunction was found within the helicopter or related components. The commercial pilot had accumulated a total of 4 hours operating with a 100 foot sling.
On September 25, 1997, at 1330 central daylight time, a Bell 206B2 helicopter, N59396, was destroyed following a loss of control while on initial takeoff climb near Anahuac, Texas. The commercial pilot, sole occupant of the helicopter, sustained serious injuries. The helicopter, owned and operated by Houston Helicopters Inc., of Pearland, Texas, was being operated under Title 14 CFR Part 133, at the time of the accident. Visual meteorological conditions prevailed for the local external load flight for which a company flight plan was filed. The helicopter was taking off after filling the water bucket when the accident occurred. The helicopter was supporting seismic operations being conducted by Grant Geophysical, Inc., near the Anahuac National Wildlife Refuge. The helicopter was summoned to deliver a bucket of water to support drilling operations. A member of the drilling crew reported observing the helicopter flying in the direction of the pond being utilized to extract the water. When the helicopter failed to return with the water bucket, the drilling crew became concerned and a search for the helicopter was initiated. The mangled wreckage of the helicopter was located in a marshy area approximately 100 feet west of a pond known as Oyster Bay Bayou. The helicopter came to rest on its right side on a northerly heading. Physical evidence at the accident site indicate that the helicopter impacted the terrain at a high rate of descend with very low forward airspeed. There were no reported eyewitnesses to the accident. A 7-foot diameter ground impression was found in the soft marshy area was nearly circular in shape. The ground impression corresponded to the collapsible water bucket that was found approximately 200 feet to the west of the resting place of the main wreckage. The 3 to 5 foot tall grass on the southern portion of the hole made by the water bucket was found pushed or laid back in a southerly direction. The 100 gallon water "Bambi" bucket, which was found configured to carry 79 gallons of water, was attached to the 100 foot long cable. The cable was found laying near the helicopter's external hook. Deep wear impressions corresponding to the steel cable being utilized in conjunction with the external load were found aft of the toe of the left skid tube, at the attaching point where it attaches to the crosstube assembly. No similar impressions were found on the other skid or cross tube assemblies. The helicopter was not equipped with any device to prevent the external load cable from becoming entangled with the helicopter's skid landing gear. Examination of the helicopter at the accident site by FAA inspectors revealed that the cabin, fuselage, tailboom, and main rotor system of the helicopter were structurally damaged. The right forward section of the fuselage separated from the airframe. Witness marks found on the collective controls indicate that the collective was in the full up position at the time of the impact. The tail boom of the helicopter was bent upwards. The main mast was bent 20 to 30 degrees at the static point. Both main rotor blades were severely damaged. The leading edges of neither tail rotor blades sustained any significant impact damage. The tail rotor assembly and the 90 degree gear box remained attached to the tailboom. A conditional release was issued to recover and transport the wreckage of the helicopter from the accident site to a secured location for further examination and testing. A wreckage layout and examination was performed at the operator's maintenance facility under the supervision of FAA inspectors. The maintenance records for the helicopter were concurrently reviewed. The review of airframe and engine records by the FAA inspector did not reveal any anomalies or uncorrected maintenance defects prior to the flight. The aircraft was found to be in compliance with all applicable airworthiness directives. The hydraulic pump, the two cyclic servos, the collective servo, the collective fitting, and the inboard half of the pilot's seat belt hinge were removed from the wreckage for further testing and examination. The removed components were examined at the Bell Plant Laboratories under the supervision of the NTSB investigator-in-charge (IIC). The fractured components were found to have fracture due to overload. The 3 servos and the pump were found to be operational and no defects were found that could have contributed to the loss of control. See enclosed report for details of the examination. In the narrative portion of the enclosed NTSB Form 6120.1/2, the pilot reported that the helicopter experienced a hydraulic failure on the previous day as result of a corroded broken fitting from the top of a servo. The pilot added that the helicopter was flown for the remainder of the day without further incident after the fitting was replaced. A signed statement was provided by the mechanic performing the repairs. The mechanic stated that the helicopter had a leaking jam nut on the left hand servo. He added that he replaced the 90 degree fitting, the jam nut, packing and "O" ring, prior to refilling the hydraulic reservoir. The pilot performed a maintenance operational check to check for leaks. The mechanic further stated that the helicopter logbook was not available at the site; however, a work order was initiated (copy enclosed) to document the maintenance performed. In the narrative portion of the NTSB form 6120.1/2, the pilot described the accident sequence as follows: After the water pick up, he visually checked the line [sling load] and climbed to clear the trees to the west [of the pond]. As he was turning south bound, the collective "went full pitch up" and he was unable to "push it back down to gain proper rotor RPM." The pilot further stated that while he had the cyclic between his knees, the cyclic began "moving violently forward and aft." The pilot added that "at 200 feet the helicopter lost 50% of the rotor RPM, turning on its side at about 100 feet." The pilot concludes by stating that at that point he had lost all rotor RPM and the helicopter fell to the ground. He added that he did not release the load because "it acted as an anchor and prevented the helicopter from gaining anymore altitude." A diagram drawn by the pilot on the narrative portion of the report showed that the accident site was located one half mile west of the pond (Oyster Bay Bayou). The wreckage diagram developed from input from the FAA inspectors that traveled to the accident site showed that the pond was located 100 feet west of the pond. The commercial pilot, who was seated in the right seat, had accumulated a total of over 12,525 flight hours and held an airline transport rating for single and multi-engine airplanes. He held commercial pilot privileges in helicopters and had accumulated a total of 3,400 hours in helicopters, which included 2,400 hours in the Bell 206 helicopter. According to personnel records provided by the operator, the pilot had accumulated 500 hours in external load operations, of which 5 hours were in long line (100 foot) operations. The operator estimated that during the 30 days preceding the accident, the pilot had accumulated approximately 24 hours with a 50 foot sling and 4 hours with a 100 foot sling. The 1973 model helicopter had accumulated a total of 7,196.1 hours. The helicopter had been recently brought back from extended storage and outfitted with a high skid landing gear system. Weight and balance calculations were made with figures provided by the operator. With an estimated external load of 790 pounds (79 gallons) at the time of the accident, the helicopter was found to be within its weight and balance limits. No evidence of pre-impact mechanical failure or malfunction was found within the airframe or related components.
the pilot's inability to maintain control of the helicopter after encountering a dynamic rollover due to entanglement of the external load cable with the left landing gear skid.
Source: NTSB Aviation Accident Database
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