What aircraft was involved and where did it happen?

The accident on 1998-06-02 involved a Hiller UH-12E, registration N4028T, at Delaplaine, AR.

Transmission Failure Leads to Forced Landing in Rice Field (N4028T)

On June 2, 1998, a Hiller UH-12E (registration N4028T) was involved in an aviation accident near Delaplaine, AR. Investigators recorded the probable cause as: Massive failure of the first stage planetary gear system due to lack of lubrication. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

A helicopter experienced a transmission failure while flying 5 feet above a rice field. The pilot turned to avoid a tree and executed a forced landing, resulting in collapsed skids and a severed tailboom.

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.

Probable cause

Massive failure of the first stage planetary gear system due to lack of lubrication.

1998-06-02: Hiller UH-12E (N4028T) — Delaplaine, AR