NTSB Identification: FTW98LA253.
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Accident occurred Tuesday, June 02, 1998 in DELAPLAINE, AR
Probable Cause Approval Date: 12/01/1999
Aircraft: Hiller UH-12E, registration: N4028T
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter was traveling in an easterly direction at an airspeed of 60 knots, while 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, as he simultaneously initiated a forced landing. During the touchdown on soft ground, both skids and the collapsed and the tailboom was severed by the main rotor blades. According to the maintenance records, the main transmission (part number 23700-9, serial number 617), which has a recommended TBO of 1,200 hours, had accumulated 1,048 hours since its last overhaul in 1993. According to the manufacturer, the 23700-9 transmissions are subject to a recurring inspection of the oil filter every 50 flight hours in accordance with Airworthiness Directive 81-17-03. According to the maintenance logbooks, the last compliance with AD 81-17-03 was 340 hours prior to the accident, on March 26, 1996. 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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of maintenance personnel to comply with and airworthiness directive, which resulted in failure of the planetary gear due to lack of lubrication. A contributing factors was the lack of suitable terrain for the pilot to execute a forced landing.

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