Accident Overview
On an unspecified date at 1145 eastern standard time, a Hélicraft 2000 Inc. Schweizer 269C-1 helicopter, registration C-FZQF, serial number 0056, was conducting ground tests following a 100-hour periodic inspection and replacement of the main transmission gearbox. The helicopter was occupied by one pilot, who was also an aircraft maintenance engineer (AME). The tests were aimed at verifying system operation, checking for leaks, and measuring tail rotor vibration. Two tests had been performed; after the second test, the pilot and a ground engineer heard a noise when engine rpm was reduced. They could not identify the source. During the third test, after about four minutes of operation, the noise was heard again and this time identified as coming from the main transmission gearbox. The pilot immediately reduced engine power. The main transmission gearbox stopped turning suddenly, causing the main rotor to separate from its shaft. The rotor rose to an altitude of approximately 150 feet above ground level and came to rest on the heliport apron about 100 feet from the helicopter. The helicopter remained in place, and there were no injuries.
Background and Maintenance
The pilot/AME was certified and qualified to conduct ground tests in accordance with existing regulations. The helicopter had a total of 3993 hours since its manufacture in 1997 and was certified, equipped, and maintained in accordance with regulations and approved procedures. The 100-hour inspection and replacement of the main transmission gearbox had just been completed. During the tests, the pilot/AME was at the controls, and another AME was positioned outside. The main transmission gearbox had been in operation for approximately 12 minutes since its last inspection.
Examination Findings
Post-accident examination revealed that the input pinion bearings of the main transmission gearbox (part number 269A5175-023, serial number S0603) were lacking lubrication. The gearbox had 2167.2 hours since new and had undergone a special inspection on 02 February 2004 after a sudden rotor stoppage. That inspection was performed by AOG Heliservices Inc., an approved maintenance organization, in accordance with manufacturer-approved procedures. The inspection included partial disassembly, visual and dimensional examination, and non-destructive testing before reassembly.
The investigation found that the input quill bearing housing was not positioned in accordance with the manufacturer's procedures, obstructing the flow of oil and causing catastrophic failure of the input quill bearings. Additionally, the independent inspection did not detect the incorrect reassembly. The report also noted that there are no mechanical means to prevent installation error when installing the input quill bearing housing, and that the force required to shear the main rotor shaft is higher than the force required to shear the six rotor head attachment bolts. Consequently, the rotor could separate from the shaft in the event of a sudden stoppage of the transmission, posing a hazard to occupants and people on the ground.
Safety Action Taken
AOG Heliservices Inc. implemented corrective actions following the event. On completion of main transmission overhauls, sudden stoppage inspections, or any other situation where the retainer is removed, the company will paint a red witness line on the retainer and transmission housing to assure alignment of oil ports. Additionally, they will run the transmission for fifteen minutes to check for oil flow and leaks at the seal and split line. These changes will be incorporated into their worksheets.
The Transportation Safety Board of Canada concluded its investigation and authorized release of this report on 11 January 2005.