Dayville, OR, USA
N263KA
Kaman K-1200
The helicopter experienced a total loss of engine power while hovering out of ground effect during a long-line logging operation. Witnesses observed the helicopter descend vertically with the rotors visibly slowing down, nose over to an inverted position, impact the ground inverted, and roll onto its left side. Initial examination of the engine revealed that when the power turbine was rotated, the engine output adapter attached to the reduction gearbox did not rotate, indicating a mechanical disconnect within the engine. Disassembly of the engine revealed severe damage to the sun gear shaft, which coupled the power turbine to the reduction gear box. Further disassembly and materials analysis disclosed an assembly error of one of the three aft planetary gear shaft roller bearings in the reduction gear box and improper crimping of the lockcup on the N1 seal and nut assembly. These two errors resulted in misalignment in the planetary gear train leading to high tooth loading in the sun gear shaft, which resulted in stripping and separation of gear teeth and loss of transmitted torque through the reduction gear box. Examination of maintenance records indicated that the bearing assembly error occurred during an overhaul of the reduction gear box by a certified repair station 822.8 operating hours before the accident. The improper crimping of the lockcup occurred during a repair by the same certified repair station performed 350.2 operating hours before the accident.
HISTORY OF FLIGHT On March 17, 2006, about 0935 Pacific standard time, a Kaman K-1200 helicopter, N263KA, collided with terrain in an uncontrolled descent following a loss of engine power while hovering out of ground effect about 16 nautical miles north of Dayville, Oregon. The commercial pilot, the sole occupant, received fatal injuries, and the helicopter sustained substantial damage. The helicopter was registered to and operated by Grizzly Mountain Aviation Inc. of Prineville, Oregon. Visual meteorological conditions prevailed and no flight plan was filed for the 14 CFR Part 133 flight. The helicopter was being used for long-line logging and operations for the day had commenced about 0700. Witnesses reported to local authorities that the pilot set down a load of logs and stated on the radio that he was going to reposition the helicopter to land at the service area. At this point, the helicopter was about 300 feet above ground level (agl), hovering, with the 200-foot long line still attached. The witnesses then heard the engine "shutdown." They observed the helicopter descend vertically with the rotors visibly slowing down, nose over to an inverted position, impact the ground inverted, and roll onto its left side. There was no fire. PERSONNEL INFORMATION The pilot held a commercial pilot certificate with a helicopter rating. Additionally, he was rated as a private pilot in single engine land airplanes. His most recent medical certificate was a second class medical issued on April 5, 2005, with the limitation, must wear corrective lenses. According to information provided by Grizzly Mountain Aviation, the pilot had accumulated a total flight time of 4,019 hours of which 3,858 hours were in helicopters and 1,646 hours were in the Kaman K-1200. In the previous 90 days, he had accumulated 267 hours, all in the Kaman K-1200. Records provided by Kaman Aerospace Corporation indicated that in September 2004, the pilot satisfactorily completed the K-1200 Pilot Familiarization Training Course at the Kaman facility in Bloomfield, Connecticut. The training included 54 hours of ground school and 15 hours of flight instruction. AIRCRAFT INFORMATION The 2002 model Kaman K-1200 helicopter, S/N A940033, was powered by one 1,500-horsepower Honeywell T5317A-1 turboshaft engine, S/N LE-81003. At the time of the accident, the helicopter had accumulated 3,193.1 hours of flight time, and the engine had accumulated 6,636.1 operating hours since new and 3,257.4 hours since overhaul. Review of the engine logbook revealed that an overhauled reduction gear box, P/N 1-030-350-16, S/N 5E003, was installed on January 10, 2005, at engine time since new of 5,813.3 hours. At the time of the accident, the reduction gear box had accumulated 822.8 hours since this overhaul, which was performed by a certified repair station. Review of the work order for the reduction gear box overhaul indicated that overhauled planetary gear shafts with serial numbers (S/Ns) 16336, 16363, and 16449 were installed. The last major maintenance action performed on the engine was conducted on August 29, 2005, at engine time since new of 6,285.9 hours. The logbook entry for this maintenance indicated the engine was sent to the same repair station that performed the reduction gear box overhaul for "repair of reported low power and high EGT." The entry stated, in part: "Inspected hot section and compressor section, replaced air diffuser, replaced combustion liner, reassembled and functionally tested I/A/W [in accordance with] Honeywell 330.2 and 330.3 manuals." At the time of the accident, the engine had accumulated 350.2 hours since this repair. Review of the daily maintenance report sheets for the helicopter from February 15, 2006, to the date of the accident revealed no listings of any uncorrected maintenance discrepancies. WRECKAGE AND IMPACT INFORMATION An on scene examination of the wreckage was conducted on March 17, 2006, by representatives from the FAA and Kaman Aerospace Corporation. According to information provided by the representatives, the helicopter came to rest inverted with the left side of the nose compartment, top and left sides of the cockpit, top of the transmission rotor shafts, left side of the landing gear boom, and left stabilizer contacting the ground. A circular debris field surrounded the helicopter with the farthest piece of wreckage located about 90 feet from the helicopter. The cargo hook on the helicopter's belly was open with the corresponding end of the long line several feet away. The long line was laid out on the ground aft of the helicopter. The line was intact, and there was no evidence of the line becoming entangled during the accident sequence. The fuselage remained intact, but was crushed, distorted and broken aft of the landing gear boom. The tail boom remained attached and was distorted. The top 18 inches of the vertical fin were broken off, and the rudder was separated from the vertical fin. The separated section of the vertical fin and the rudder were found within the debris field. All four main rotor blades were broken into sections; all of the sections were accounted for in the debris field. According to the Kaman representative, "the rotor blade sections were in relatively large pieces denoting a slow rotor speed at impact." During examination of the helicopter at the accident site, 80 gallons of fuel were drained from the helicopter's fuel system, and the fuel filter and fuel samples appeared to be clean. The wreckage was recovered from the accident site and transported to Specialty Aircraft in Redmond, Oregon, where it was further examined by the FAA and Kaman representatives on March 20, 2006. The transmission, rotor shafts and hubs remained together as a single unit, but the unit sustained heavy impact damage. The engine-to-transmission drive shaft was separated into 3 sections. The fracture surfaces on the drive shaft showed no signs of fatigue. Inspection of the engine revealed that the power turbine could be rotated by manually turning the second stage power turbine wheel. When the power turbine was rotated, the engine output adapter attached to the reduction gearbox did not rotate, indicating a mechanical disconnect within the engine. The engine was removed from the helicopter and sent to the facilities of Honeywell in Phoenix, Arizona for further examination. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy of the pilot was conducted by the Medical Examiner Division of the Oregon State Police in Clackamas, Oregon. Toxicology tests conducted by the FAA's Toxicology and Accident Research Laboratory were negative for carbon monoxide, cyanide, ethanol and drugs. TESTS AND RESEARCH The engine was examined at the Honeywell facilities in Phoenix, Arizona on May 1 and 2, 2006, under the supervision of the NTSB investigator-in-charge (IIC). Disassembly of the engine revealed severe damage to the sun gear shaft (P/N 1-130-192-04, S/N 71037), which coupled the power turbine to the reduction gear box. Specifically, the center section of the sun gear on the forward end of the shaft was completely milled away, well into the gear shaft rim. The three planetary gear shafts (P/N 1-030-193-01, S/Ns 16336, 16363, and 16449) displayed damaged and missing teeth on their aft gears, which mated with the sun gear. There was metal debris adhering to all of the gear shafts. A large amount of metal debris, including pieces that appeared to be fragments of gear teeth, was found in the inlet housing, which covers the reduction gear box. Each planetary gear shaft was supported at its aft end by a roller bearing, the outer race of which was pressed into a bore in the aft plate of the planetary gear carrier assembly. The aft roller bearing that supported planetary gear shaft S/N 16336 was found missing its cage, and the individual rollers were clustered together, such that a gap without rollers extended approximately 90 degrees around the circumference of the bearing. Pieces of the missing cage were located among the debris in the inlet housing. The lockcup for the N1 seal and nut assembly, located on the forward end of the N1 compressor turbine shaft, was found disengaged, and the nut assembly had backed off of the threads on the compressor shaft. There was evidence of heavy rotational contact between the forward side of the nut assembly and the aft face of the #21 roller bearing. The #21 roller bearing, which supports the N2 power turbine shaft, was severely damaged. Specifically, the rollers were worn to a shape that locked them in their cage, which prevented them from rotating. The damaged bearing had allowed the N2 power turbine shaft to contact and rub the inside of the N1 compressor turbine shaft. (The N1 shaft is hollow, and the N2 shaft is housed within it.) At the request of the NTSB IIC, Honeywell performed materials and engineering analysis on multiple components from the engine. These components included the sun gear shaft, the three planetary gear shafts, their bearings, the planetary gear carrier assembly, the N1 seal and nut assembly, its lockcup, and the #21 roller bearing. The findings of the materials and engineering analysis were, in part: 1. The aft shoulder of the outer race on the aft roller bearing that supported planetary gear shaft S/N 16336 exhibited four half moon shaped indentations, consistent with the spacing of four adjacent rollers installed in the bearing cage. The indentations were indicative of alignment-related assembly damage. 2. Examination of the corresponding bore in the aft plate of the planetary gear carrier assembly revealed a series of axial drag marks from a reluctant assembly of the aft roller bearing into the bore. These axial marks were overlaid by circumferential marks due to rotation of the bearing within the bore during operation, indicating that the axial marks were made during installation, not during disassembly. 3. Planetary gear shaft S/N 16336 exhibited fatigue separations on several of the aft gear teeth that mated with the sun gear. The case depth, case hardness, and core hardness of the planetary gear teeth were as specified. 4. Examination of the lockcup for the N1 seal and nut assembly revealed evidence that the lockcup was not properly engaged into the nut assembly. Specifically, five of the available six areas on the lockcup were crimped; however, the crimps were all notably shallow. On the basis of the materials and engineering analysis, Honeywell developed the following chain of events leading to excessive wear of the sun gear shaft: 1. The aft roller bearing that supported planetary gear shaft S/N 16336 was improperly assembled, resulting in damage to the bearing. 2. Operation of the aft bearing with the shoulder damage at a spacing identical to four adjacent roller pockets resulted in the rollers pounding the cage pockets, eventually fatiguing and breaking the cage cross-webs. After the cross-webs all separated from the cage rings, the rollers all clustered together, resulting in an approximately 90 degree gap without rollers. 3. The gap without rollers induced a periodic high misalignment in planetary gear shaft S/N 16336 each time the gap passed through the load zone. This action led to fatigue failures to the teeth of the planetary gear and an increase in vibration. 4. Engine vibration from the failing planetary gear train along with the improperly crimped N1 seal and nut assembly lockcup loosened the nut. The nut then backed off and jammed into the #21 bearing. 5. Contact between the N1 seal and nut assembly and the #21 bearing led to sliding of the bearing's rollers resulting in excessive wear to the rollers. Radial wear continued in the bearing, eventually allowing the N2 shaft to make contact with the inside of the N1 shaft. 6. Rubbing of the shafts produced further misalignment in the planetary gear train leading to high tooth loading in the sun gear shaft, which resulted in stripping and separation of gear teeth and loss of transmitted torque through the reduction gear carrier assembly. ADDITIONAL INFORMATION The wreckage was released to a representative of the owner on December 6, 2006.
The improper overhaul of the reduction gear box assembly and improper installation of the N1 seal and nut assembly lockcup by maintenance personnel, which resulted in failure of the reduction gear box and a total loss of engine power. A contributing factor was the pilot's failure to maintain adequate rotor rpm following the power loss, which resulted in an uncontrolled descent to ground impact.
Source: NTSB Aviation Accident Database
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