What aircraft was involved and where did it happen?

The accident on 1983-09-30 involved a Hughes 369D (500), registration N8693F, at Provo, UT.

Helicopter Sustains Tail Boom Strike During Autorotation Landing on Test Flight (N8693F)

On September 30, 1983, a Hughes 369D (500) (registration N8693F) was involved in an aviation accident near Provo, UT. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

During a test flight to track and balance the main rotor, a helicopter experienced an engine failure after the fuel filter light flickered. The pilot performed an autorotation, but on landing the main rotor struck the tail boom. Investigation found a loose B nut on a differential pressure line.

Background

The helicopter was conducting a test flight to track and balance the main rotor system and to complete a 100-hour inspection. Prior to departure, maintenance personnel noted an occasional flicker of the fuel filter light, which was attributed to a possible wiring issue.

Flight Events

After takeoff, the fuel filter light flickered several more times but never illuminated steadily. Within less than a minute of flying time, the pilot felt two quick yawing motions. He initiated a 180-degree turn to return for landing. After completing 90 degrees of the turn, the N2 turbine speed decreased to 95%, then surged to 105%, followed by the engine ceasing to run. The pilot then performed an autorotation.

Landing and Damage

During the landing on soft, wet terrain, the helicopter rocked forward, causing the main rotor blades to strike the tail boom.

Examination

An examination of the helicopter revealed that a B nut on one of two differential pressure lines connected to the fuel filter differential pressure switch was loose. During the inspection, the B nut separated from its attachment point by a half turn under finger pressure.

1983-09-30: Hughes 369D (500) (N8693F) — Provo, UT