Accident Synopsis
The helicopter was traveling in an easterly direction at an airspeed of 60 knots, maintaining a constant 5-foot clearance over the rice field, when the transmission failed. The pilot turned the helicopter to the right to avoid a tall tree and simultaneously initiated a forced landing. During touchdown on soft ground, both skids collapsed, and the tailboom was severed by the main rotor blades.
Maintenance History
According to maintenance records, the main transmission (part number 23700-9, serial number 617) had accumulated 1,048 hours since its last overhaul in 1993, against a recommended TBO of 1,200 hours. The manufacturer stated that 23700-9 transmissions are subject to a recurring inspection of the oil filter every 50 flight hours per Airworthiness Directive 81-17-03. The last compliance with AD 81-17-03 was 340 hours prior to the accident, on March 26, 1996.
Examination Findings
Examination of the transmission by the manufacturer's representative revealed a massive failure of the first stage planetary gear system due to lack of lubrication.