Peach Springs, AZ, USA
N357NT
Aerospatiale AS350BA
The helicopter landed hard following a loss of directional control during a precautionary landing after a hydraulic system failure, with the main rotor blades cutting off the tail boom. This was a tour flight that was en route back to the departure airport when a complete hydraulic system failure occurred and the pilot decided to make a precautionary landing at a nearby airport. He had planned on conducting a run-on landing; however, during the approach the airspeed dropped to 30 knots. The helicopter's nose dropped and it started to spin to the left. The pilot pulled back on the cyclic enough to get the nose up; however, forward airspeed continued to decay and the rotation rate increased. The pilot said that the flight controls were not responding, and he believed the only way to stop or slow the rotation was to shutdown the engine. The helicopter completed two revolutions before it impacted the ground in a nose level attitude, 180 degrees from its original direction of travel. A witness to the accident reported the altitude of the helicopter as it began to spin was about 30-50 feet above the ground and he saw the main rotor blades cone upward as it fell to the ground. For a hydraulics failure, Federal Aviation Administration approved flight manual required the pilot to reduce the collective pitch and adjust the airspeed between 40 to 60 knots in level flight. The pilot was then instructed to cut off the hydraulic pressure by activating the collective lever pushbutton, and to make a flat approach over a clear landing area and land with forward speed. During examination of the hydraulic pump, investigators noted that the coupling sleeve splines were worn beyond serviceable limits. They also noted the general condition as rust colored, and no lubrication was found inside the pump housing or coupling sleeve splines. A company maintenance work order contained a serviceable tag for the hydraulic pump assembly. The serviceable tag that the operator's maintenance personnel wrote said that the hydraulic pump was "inspected, cleaned filter, new O rings installed on connections, inspected coupling, new pump assembled." The maintenance records also revealed that the assembled hydraulic pump was installed 15 days prior to the accident and had been in service for 74.6 hours when it failed. A metallurgical examination of the hydraulic pump revealed that it had failed due to the wearing away of the splines on the coupling sleeves. The wear was due to insufficient lubrication and soft splines on both coupling sleeves. The failure mode was assisted by an increase in internal rotational resistance at operating temperatures. The hardness testing indicated that the case hardened layer on the splines was not deep enough and the hardness, within the layer, was slightly below the specified range. The inner surfaces of the gear bearings displayed rubbed areas, consistent with hard contact, and areas of bluing, consistent with elevated temperatures. Examination of the coupling sleeves revealed a total loss of inwardly protruding spline material and hardness below the design requirements. The manufacturer's maintenance manual requires that the pump drive shaft, coupling sleeves, and bearing be packed with "abundant" grease during assembly. The examination found only a trace amount of grease in the coupling sleeves that did not satisfy the "abundant" requirement specified in the manufacturer's maintenance manual. There was rust on the front retaining rings and bearings, which indicated that there was insufficient grease in the splines to retain it or lubricate the splines.
HISTORY OF FLIGHT On September 11, 2002, at 1700 mountain standard time, an Aerospatiale AS350BA, N357NT, experienced a hydraulic failure during cruise flight and landed hard while making a precautionary landing at the Grand Canyon West Airport (1G4), Peach Springs, Arizona. Heli-USA Airways, Inc., operated the helicopter under the provisions of 14 CFR Part 135 as a tour flight. The helicopter sustained substantial damage. The pilot and five passengers were not injured. A sixth passenger sustained minor injuries. Day visual meteorological conditions prevailed for the tour flight over the Grand Canyon, and a company visual flight rules (VFR) flight plan had been filed. The flight departed the McCarran International Airport (LAS), Las Vegas, Nevada, about 1600. The flight was returning to LAS when the hydraulic failure occurred. According to the operator, the flight was returning to LAS when the helicopter had a "complete" hydraulic failure. The pilot was in the vicinity of Peach Springs Airport, and made the decision to make a precautionary landing. The helicopter landed hard, the main rotor blades flexed down and cut off the tail boom. According to the pilot's written statement, the flight to the Grand Canyon was uneventful. He made a radio call indicating that he was crossing the Grand Wash Cliffs area heading towards the Bat Towers. Five miles before entering the canyon he heard an aural alarm and saw that the hydraulic light was illuminated on the caution panel indicating a hydraulic failure. The airspeed was at 100 knots so he slowed the helicopter down between 40 to 60 knots per the recommended procedures, and turned off the caution horn using the button on the systems control console. After turning the helicopter towards the Peach Springs Airport, he depressed the hydraulic cutoff button on the collective control. During the approach he reported making his radio calls to the airport traffic, as well as coordinating with a sister ship to transport his passengers back to the operator's facility after landing. The pilot informed his passengers of the mechanical problems and noted no additional issues with the flight to the airport. He indicated that the hydraulic off indications were "felt" in the flight controls, and intended to do a run on landing in the new concrete landing/parking ramp area on the field. He reported that everything was normal until the helicopter was about 25 feet short of the ramp area. As he continued the approach, the flight controls increased in stiffness. He noted the airspeed was now 30 knots, and about 10 feet before the ramp at an altitude of 15 to 25 feet above ground level (agl). The nose pitched down, and the helicopter started to rotate. He pulled back on the cyclic enough to get the nose back up, which slowed the helicopter more but increased the rotation speed. The pilot thought they made two complete rotations, and reported that the flight controls were not responding. In order to slow or stop the rotation of the helicopter, he "cut off" the engine. The rotation slowed, and the helicopter started to settle to the ground. The pilot attempted to keep the helicopter in a level attitude, and it impacted in a near vertical descent from about 10 to 20 feet agl. The helicopter came to rest facing 180 degrees from its original direction of travel. The pilot reported that one of the passenger's feet had become trapped under the helicopter during the accident sequence. Airport personnel and pilot's from other companies assisted with pushing the helicopter up in order to remove the passenger's foot; there were no other injuries. In an interview with the National Transportation Safety Board investigator-in-charge (IIC), the pilot reported that the flight was about 3 minutes from the airport when he heard the aural caution horn and saw the hydraulic light illuminate. He also recalled that the passenger seated behind him was over 6 feet tall. The passenger's foot had been extended all of the way forward, resting by the pilot's side door, and had become trapped during the accident sequence. The pilot reported that the helicopter made two full revolutions to the right, and he had in full left pedal. He also reported that he had landed with a 4-knot tailwind. A witness to the accident (a company helicopter tour pilot) submitted a written statement to the Federal Aviation Administration (FAA). He reported that he was at 1G4 refueling his helicopter when he heard the accident pilot radio and that he had experienced a complete hydraulic failure. The witness asked where the accident pilot intended to land the helicopter, to which the pilot replied that he was headed for the large parking apron located on the northeast side of the runway. The witness reported that the helicopter was heading in a southerly direction. He observed the helicopter approach the landing area and said it was a little fast, between 40-55 knots. As the helicopter made its final approach to the parking apron, it was still a little bit high. The helicopter started to pitch up with a slow roll to the left. The witness reported that the helicopter's nose pitched down, all the while doing a complete 360-degree turn to the left. He estimated the helicopter's altitude between 30-50 feet. The witness began yelling on the radio for the accident pilot to get the nose of the helicopter up and not let it strike the ground in a nose down attitude. After completing the 360-degree turn, the witness reported that the helicopter had lost altitude in the left turn, the nose was slowly starting to pitch back to level flight, and the main rotor blades were starting to slow down. He reported that he could see the main rotor blades starting to cone in an upward direction, an indication to him that the main rotor blades were starting to slow down. The helicopter impacted the ground in a level attitude, and was covered by a large dust cloud. The witness could not see anything for about 10-15 seconds. He shut down the engine of his helicopter and ran towards the accident helicopter. When he was able to see the helicopter again, he noted that the tailboom had separated and was lying near the right side of the fuselage. He then assisted with the welfare of the passengers on the accident helicopter. PERSONNEL INFORMATION A review of the FAA airman records revealed that the pilot held a commercial pilot certificate with helicopter and instrument helicopter ratings. The pilot also held a mechanic certificate with ratings for airframe and powerplant. The pilot held a second-class medical certificate issued on August 28, 2002. It had no limitations or waivers. The pilot reported his total flight time as 4,025 hours, with 1,785 hours in the accident make and model. He had logged 134 hours in the last 90 days, and 21.6 hours in the last 30 days. According to personnel records obtained from the operator, the pilot had flown 2.3 hours on the day of the accident. The operator had employed the pilot since 2000. At the time of the accident he was the Assistant Director of Operations, as well as a company flight instructor and mechanic. AIRCRAFT INFORMATION The helicopter, serial number 1549, was originally issued a standard airworthiness certificate in 1987, as an Aerospatiale AS350B, but was converted to a BA and issued a standard airworthiness certificate on May 9, 2000. A review of the helicopter's daily flight logbook revealed a total airframe time of 8,387.7 hours at the last 100-hour inspection, completed on August 28, 2002. The airframe total time at the time of the accident was 8,451.7 hours. A Turbomeca Arriel 1B engine, serial number 4474, was installed on the helicopter. The engine total time was 8,824.5 hours at the last 100-hour inspection dated August 28, 2002. The engine had accrued 2,830.7 hours since overhaul, and 74.6 hours since the last 100-hour inspection. A review of the operator's maintenance work order for the helicopter (number 08270215491, dated August 28, 2002, revealed that under the Discrepancy heading, the hydraulic pump bearing was due for replacement. The operator's corrective action by maintenance personnel indicated, "replaced hyd[raulic] pump assembly TSN 0, 28Aug02." The serviceable tag issued for the hydraulic pump assembly, serial number 10318827, contained the following information, "inspected, cleaned filter, new O rings installed on connections, inspected coupling, new pump assembled." According to the operator, the helicopter had 88.44 gallons (62 percent) of Jet-A fuel on board prior to departure from LAS. Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the helicopter prior to departure. For a hydraulics failure, the operator's FAA approved AS350 flight manual states in part, "calmly reduce collective pitch and adjust the airspeed to between 40 and 60 knots (74 to 111 km/hr) in level flight. Cut off the hydraulic pressure, using collective lever pushbutton. Make a flat approach over a clear landing area and land with slight forward speed." AIRPORT INFORMATION The Airport/ Facility Directory, Southwest U. S., indicated Grand Canyon West Airport (1G4) runway 17/35 was 5,058 feet long and 60 feet wide. The runway surface is composed of asphalt. TESTS AND RESEARCH Investigators from the FAA and American Eurocopter examined the wreckage at Lone Mountain Aviation, Inc., North Las Vegas, on September 19, 2002, under the supervision of the Safety Board IIC. Examination of the hydraulic pump assembly revealed a rust color surrounding the interior of the pump to include the coupling sleeve (S40 coupling). The visible splines of the coupling sleeve were worn down beyond serviceable limits, and investigators noted a lack of lubrication (grease) inside the coupling, as well as bluing inside the pump. The Safety Board IIC retained the hydraulic pump and coupling for further examination by the Safety Board's Materials Laboratory in Washington, DC. The Safety Board's Materials Laboratory examined the hydraulic pump drive, and a specialist prepared a factual report. The following paragraphs summarize pertinent parts of the report. Section 1-17 of the maintenance manual described servicing recommendations for the main hydraulic section. It specified that the hydraulic pump drive shaft and bearing be checked and greased at 500-hour intervals. An illustration in the manual indicates that the lubrication is accomplished by packing the hub with abundant grease before the coupling sleeve is installed. Examination of the coupling flange revealed a tan colored deposit on its inner surface. Examination of the elastic coupling revealed a similar tan deposit, a raised letter "U," and raised characters "PB 72". The cylindrical bearing support located on the mounting plate was permanently riveted to it and displayed no indications of looseness. The hydraulic pump was also bolted to the mounting plate. Examination of the hydraulic pump revealed that material had been worn from the splines of the driving gear, which protruded outside of the front body to connect with the internal splines on the coupling sleeve. There was a red powdery deposit on the splines and the adjacent components, consisting of the retaining ring, the O-ring, and the bearing. The O-ring provided a seal between the driving shaft and the end of the coupling sleeve to prevent the escape of the grease applied to the splines. The Materials Laboratory specialist extracted several components from the pumping assembly. He observed a hard black circumferential deposit on the shaft portion of the driving gear that corresponded with the location of the bearing seal, and he measured it at 0.0015-inch thick. He removed a piece of the splined portion of the driving gear, cut it perpendicular to the axis of the shaft portion of the driving gear, mounted it and polished it for metallurgical examination. He chemically etched the polished metallurgical mount to reveal a uniform microstructure with a darker-etching surface layer that was consistent with a case hardening process. The specialist performed micro-hardness testing at various depths from the surface of a spline root. He recorded the hardness in the Knoop scale with a 500-gram load (HK/500) and converted it to Rockwell C-scale (HRC) for comparison with the engineering requirements. The hardness measurements indicated that the case hardened layer was not deep enough, and was slightly below the specified value throughout its thickness. Examination of the cross section through the pump splines revealed that each spline was missing a uniform amount of material, and that the remaining material had been deformed in the direction of rotation. One spline displayed a crack that was continuous through the spline, and inclined approximately 10 degrees outwards. The crack had propagated along the grain boundaries. The microstructure displayed the needle-like features consistent with a predominantly martensitic structure. Separation and examination of the pumping assembly revealed surface smearing on opposing inner faces of the front and rear bearings. Compensation seals and anti-extrusion seals were located in grooves at the front and rear ends of the pumping assembly. These seals isolate the low-pressure side (intake) of the pumping assembly from the high-pressure (output) side. The specialist measured the dimensions of the assembled pumping body for comparison with the corresponding dimension on the central body. The measurements suggested that the seals were fully compressed within their grooves in their respective bearing and that the front and rear bodies were also in contact with the bearing. The examination revealed that all surfaces of the front body displayed a black finish. The surfaces of the rear body, with the exception of the inner surface, displayed a similar black finish. The inner surface of the rear body displayed bare metal with what appeared to be machining marks on the upper portion. The areas containing the machining marks also contained a black deposit, possibly remains of the black finish. The machining marks consisted of concentric curving arcs, which were present on the surface inside and outside of the O-ring. The O-ring itself did not display any downwardly curving marks or surface disturbance. The inner surface, adjacent to the O-ring groove, displayed an imprint left by the central body. The imprint was not on the top of the rear body, but there was an indication of the continuation of the shape of the central body in this area. There was an indication of an imprint of the rear bearing. Measurement of the machining lines using an OGP Smartscope indicated that a cutting tool of approximately 3.8-inches diameter produced them. The measurements also revealed that the front body was 0.710-inch thick and the rear body was 0.705-inch thick. The low-pressure connection and the high-pressure connection remained attached to the central body of the hydraulic pump. The low-pressure connection incorporated a magnetic plug intended to attract and hold any magnetic material in the hydraulic fluid passing across it. The specialist removed the magnetic plug and noted no contamination. Examination of the central body revealed that both end faces displayed surface patterns similar to the patterns on the mating surfaces of the front and rear bodies. Two of the assembly bolt holes displayed bare metal surfaces, and two holes displayed the "gold" surface similar to that on the exterior surface of the central body. The "gold" color extended across the rear face of the central body from one of the colored holes and the adjacent exterior surface of the central body. Examination of the inside chamber of the central body revealed shallow grooves on the chamber walls, adjacent to the low pressure and high-pressure fluid holes. The width of the grooves was similar to the thickness of the pumping gears. Coupling sleeve The coupling sleeve connects the belt driven pulley (via the coupling flange and the elastic coupling) to the splines on the pump driving gear shaft. Examination of the sleeve reveale
the pilot's failure to maintain an adequate airspeed and main rotor rpm during the landing approach as prescribed in the hydraulic pump failure emergency procedures found in the rotorcraft flight manual, thus resulting in a loss of control of the aircraft and the subsequent crash. Contributing to the accident was the failure of the hydraulic pump due to excessive coupling spline wear which was caused by the application of insufficient lubrication by the operator's maintenance personnel during pump installation and the improper manufacturing of the couple sleeve.
Source: NTSB Aviation Accident Database
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