DEN05TA113
DEN05TA113

On July 19, 2005, approximately 1515 mountain daylight time, a Hughes 369FF single-engine helicopter, N530TJ, was destroyed when it impacted trees and terrain following a loss of control while hovering approximately 20 miles west of Loveland, Colorado. The commercial pilot, who was the sole occupant, sustained minor injuries. The helicopter was operated by the United States Department of Agriculture (USDA) Forest Service Rocky Mountain Region (Region 2) for public use firefighting missions, and registered to Utility Aviation Inc., Fort Collins, Colorado. Visual meteorological conditions prevailed, and a flight plan was not filed. The flight originated from a staging area west of Loveland at 1504.

According to the pilot's statement, the helicopter was being used to support firefighting operations in the area and was attempting to deliver supplies via external load. The helicopter was equipped with a 100-foot long line and a 20-foot choker, the external load weighed 615 pounds, and the helicopter weighed a total of 3,000 pounds.

Prior to the approach, the pilot over flew the intended landing location and was informed that the winds were from the west approximately 7 knots. The pilot performed a hover check approximately 1/2 mile east of the intended landing zone (LZ) over a valley. The pilot moved the helicopter west to the LZ at a speed just above effective translational lift and came to a hover with the load approximately 30-40 feet over the landing spot. The pilot checked the engine and operating instruments and all systems indicated normal. "No unusual noises or vibrations."

The pilot began looking down and outside the helicopter when he felt a yaw to the right. The pilot noticed that he was "depressing the left [pedal] more as I pushed on the left to stop a right turn." The helicopter then made an "uncommanded turn to the right and began spinning right." The helicopter made two to three rotations to the right; the pilot jettisoned the cargo portion of the long line and lowered the collective. "As the aircraft stabilized in a glide, [pilot] attempted to regain control of the descent by adding power/pitch to the main rotor. When [pilot] did this, the aircraft immediately started spinning again, two quick rotations." The pilot lowered the collective and began a glide into the trees. Subsequently, the helicopter impacted trees and terrain and came to rest on its left side. The accident site was located at an elevation of 7,700 feet on a 10-20 degree slope.

According to a witness, who was assisting near the LZ, the surface winds were light at the time; however, it had been a "pretty windy day." As the helicopter approached the LZ, "everything was normal when he did a 180-degree turn. The load was fairly stable below him and the ship did a quick 180. Paused briefly, did another (180), completed to the 360, and then kept slowly spinning...The flight pattern started getting a little more erratic, as far as the load of his, the sling was kind of penduluming...swinging." The witness then observed the helicopter release the external load. The witness lost sight of the helicopter behind a tree and heard the impact. The witness responded to the accident site and the engine was still running. Shortly after that, "the engine cut."

According to the United States Forest Service (USFS), at the time of the accident, the temperature was 32 degrees Celsius and a calculated density altitude of 11,465 feet.

During a telephone interview conducted by the NTSB IIC, the pilot reported he had accumulated 1,600 total rotorcraft hours, and 65 hours in the accident helicopter. The pilot had accumulated approximately 150 total hours in external load operations, with approximately 8 total hours in the accident helicopter. In addition, the pilot had approximately 10 years experience in single-engine air tankers.

The helicopter was examined at the accident site by the Federal Aviation Administration and the USFS. The helicopter was recovered and transported to a facility in Greeley, Colorado, for further examination.

On August 16, 2005, the NTSB investigator-in-charge, a representative of Boeing, and a representative of the USFS examined the helicopter. Examination of the airframe revealed the fuselage was crushed and deformed. The tail boom was fractured into several fragments. Damage to the tail boom was consistent with impact forces and main rotor blade strikes. The main rotor hub assembly and components were destroyed and consistent with sudden stoppage. All five main rotor blades were separated from the rotor head and exhibited fractured and bent spars, skin delamination, cuts and gouges.

The main transmission rotated when the main rotor system was turned by hand. Continuity was established to the tail rotor output pinion and the engine input quill when the transmission was rotated. The tail rotor drive shaft was fractured into multiple segments which corresponded to the fractures in the tail boom structure. The tail rotor gearbox was fractured across the case elbow. The tail rotor gearbox output quill rotated when turned by hand. One tail rotor blade was fractured into three sections with one fracture at the pitch change arm, one at the root fitting, and one approximately 10 inches from the blade end. The other tail rotor blade was fractured at a point just past the blade doubler.

The longitudinal and lateral cyclic flight controls and collective flight controls exhibited continuity from the controls to the upper flight controls. The upper flight controls were damaged; however, movement of the controls operated the flight control links. Anti-torque flight control continuity was established from the foot pedals to the separated control rod located at the aft fuselage station 100. The tail rotor control rods and bell cranks were bent and fractured in numerous locations.

Examination of the engine revealed damage consistent with the impact to the exhaust and combustion sections. Continuity was established to N1 and N2 control linkage from the throttle and collective to the fuel control and power governor. No anomalies that would have precluded operation were noted with the airframe systems and engine.

A review of the external load manifest for the accident flight revealed the load consisted of long line, swivel, lead line, net, remote hook, 14 bladder bags of water, and hose. The USFS "manifest preparer" calculated the load to be 632 pounds (lbs). After the accident, a review of the actual weights and equipment on the external load revealed the USFS manifest preparer miscalculated the load. The total for the external load at the time of the accident was 732 lbs. The pilot was not aware of the miscalculation at the time of the accident.

Prior to any external load flight, the pilot was responsible to complete a USFS FS-5700-17, Interagency Load Calculation, form. On July 18, 2005, the pilot completed the form based on the following: departure pressure altitude 5,000 feet; departure temperature 25 degrees Celsius; destination pressure altitude 9,000 feet; destination temperature 30 degrees Celsius; and helicopter operating weight 2,515 lbs. A review of that form revealed the pilot incorrectly completed the form in several areas; performance reference, gross weight, adjusted weight, selected weight, operating weight and allowable payload. The pilot's non-jettisonable allowable payload was calculated to be 465 lbs for hover in and out-of-ground effect (IGE and OGE), and a jettisonable allowable payload of 1,235 lbs for OGE. The improperly completed form was signed off by the pilot and USFS Helicopter Manager. A recalculation was performed by a USFS Helicopter Inspector Pilot after the accident. The recalculation revealed the non-jettisonable IGE and OGE allowable payloads were 569 lbs and 259 lbs respectively, and the jettisonable OGE allowable payload was 379 lbs.

On the day of the accident, the pilot completed another Interagency Load Calculation form based on the following: departure pressure altitude 9,500 feet, departure temperature 35 degrees Celsius; and helicopter operating weight of 2,454 lbs. A review of that form revealed the pilot incorrectly completed the form in several areas; adjusted weight, selected weight, and allowable payload. Based on the conditions listed by the pilot, the pilot's calculated jettisonable OGE allowable payload was 646 lbs. The improperly completed form was signed off by the pilot and the USFS Helicopter Manager. According to the USFS Helicopter Inspector Pilot who reviewed the form after the accident, the allowable payload calculations could not be performed because the pressure altitude and temperature values exceeded the manufacturer's performance limitations for the helicopter.

According to the USFS, at the time of the accident, the gross weight of the helicopter was 3,072 lbs, based on an aircraft weight of 1,860 lbs; pilot 200 lbs; fuel 280 lbs; and an external load of 732 lbs. The reported actual environmental conditions were pressure altitude 8,000 feet, and temperature 32 degrees Celsius. In accordance with the Rotorcraft Flight Manual, CSP-FF-1, dated August 14, 1998, with revision 5, dated October 3, 2003, Page 8-4, Figure 8-3, Hover Ceiling, Out of Ground Effect, Engine Air Particle Separator Inlet with Mist Eliminator, indicated that the maximum gross weight for OGE was 2,940 pounds.

According to the Federal Aviation Administration's Rotorcraft Flying Handbook, FAA-H-8083-21, Chapter 11, LTE at Altitude, "At higher altitudes, where the air is thinner, tail rotor thrust and efficiency is reduced. When operating at high altitudes and high gross weight, especially while hovering, the tail rotor thrust may not be sufficient to maintain directional control and LTE can occur. In this case, the hovering ceiling is limited by tail rotor thrust and not necessarily power available. In these conditions gross weights need to be reduced and/or operations need to be limited to lower density altitudes."





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