Engine failure identified as cause of fatal South Korean military helicopter crash

By Kim Seung-yeon

SEOUL, Sept. 10 (Yonhap) -- A sudden engine failure has been identified as the main cause behind the deadly crash of a military helicopter in February that killed two soldiers, Army officials said Thursday.

The AH-1S Cobra helicopter of an Army aviation unit crashed during an emergency landing familiarization training in Gapyeong County, about 55 kilometers northeast of Seoul, on Feb. 9, killing the two warrant officers on board. No civilian damage was reported.

The military had since been investigating to determine the exact cause of the crash.

According to official findings, an internal cylinder in the helicopter engine was slightly misaligned, causing the engine's central drive shaft to wobble as it turned.

The wobble caused violent vibrations, and the spinning shaft began whipping around widely like a jumping rope, known as "shaft whirling," the Army said.

When the pilot pushed the throttle back up to climb, the spinning power shaft slammed into a second spinning shaft, instantly generating extreme heat that melted the components, ultimately shutting down the engine.

"We have concluded that the cause of the accident was a physical factor -- an engine flameout resulting from a fault in the internal cylinder in the aircraft engine's exhaust diffuser, rather than environmental or human errors," an Army official said in a press briefing.

The Army said it plans to consult with the Joint Chiefs of Staff to consider accelerating the helicopter's retirement. Retirement for the crashed AH-1S, first introduced in 1988 and deployed in 1991, was planned to begin in 2028.

"We will also work closely with the Defense Acquisition Program Administration to adjust the operational deployment plan for its replacement, the LAH-1 Miron, to ensure its stable fielding," it said.

To strengthen oversight, the Army said it will transfer aviation safety management functions and personnel from the Army Aviation Command to the Army Headquarters Combat Readiness and Safety Group by April next year.

"For airfields operating both helicopters and drones, we will improve the safety management system by transitioning from individual checks to an integrated inspection for manned and unmanned platforms," the Army said.