On January 23, 2001, a Hughes 369D (registration N8353F) was involved in an aviation accident near Ely, NV. Investigators recorded the probable cause as: The mechanic's inadvertent activation of the bleed valve, which resulted in a loss of engine oil and loss of engine power while in cruise flight. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A single-engine helicopter lost engine power after a mechanic inadvertently engaged a bleed valve during radio installation, allowing oil to leak out. The pilot performed an autorotation, but main rotor blades flexed and severed the tail boom upon landing.
Accident Overview
A single-engine helicopter experienced a loss of engine power at 9,500 feet after engine oil was inadvertently pumped overboard. The pilot executed an autorotation landing to a field at the base of mountains. The pilot reported a smooth and light touchdown, but the main rotor blades flexed and severed the tail boom.
Maintenance Actions
Prior to the accident flight, a company mechanic replaced the torque gauge due to needle "bounce." The mechanic bled the torque system and reinstalled a radio that had been removed to facilitate the work. During the radio installation, the mechanic inadvertently engaged the bleed valve, which is located behind the instrument panel. This allowed oil to flow out of the engine from behind the instrument panel.
Outcome
As a result of the accident, the operator rerouted the torque system bleed line toward the pilot's feet so that pilots could detect an inadvertent oil leak in the future.