Engine Defect Caused Army Cobra Helicopter Crash in February

Army Announces Results of Helicopter Crash Investigation

The Army Cobra helicopter (AH-1S) crash that occurred in Gapyeong, Gyeonggi Province last February was found to have been caused by an engine failure in midair due to a defective cylinder inside the aircraft’s engine exhaust diffuser.

On September 10, the Army Central Accident Investigation Board announced the results of its investigation at the Ministry of National Defense in Yongsan, stating that "the cause of the accident was an engine stoppage resulting from a defect in the cylinder inside the aircraft engine's exhaust diffuser."

Immediately after the accident, the Army formed a joint Central Safety Accident Investigation Board with civilian, government, and military participants to investigate the incident.

The Cobra helicopter carries two pilots. The reporter boarded the front seat, responsible for the weapon system, facing the helicopter's wind.

The accident helicopter was conducting takeoff and landing training to master emergency procedures at Gapyeong Airfield in Gyeonggi Province at around 11:00 a.m. on February 9. During the ascent for the seventh round of training, black smoke appeared after takeoff, and the engine stopped. The helicopter, having lost power, rapidly descended and crashed into a river near Sinhagyo, about 760 meters north of the runway's end.

Analysis of the onboard audio and video recorders, the pilots' position information terminal, and surrounding CCTV footage showed that speed, altitude, and attitude were normal at takeoff. However, 21 seconds into the flight, smoke appeared and the engine stopped; various instrument readings and the main rotor RPM then plummeted. The helicopter hit the ground 12 seconds after the engine stopped.

The investigation board explained that there was no evidence of damage from foreign objects inside the engine. Analysis of the T53 turboshaft engine installed in the accident helicopter confirmed that the power shaft and the compressor shaft seized due to heat generated by friction between them, and the rotation of both shafts stopped, leading to engine failure.

In particular, it was found that the central axis of the cylinder inside the rear exhaust diffuser deviated from the engine's central axis, causing vibration while the power shaft rotated. During the emergency procedure training at the time of the accident, torque was reduced and then increased again for takeoff, which increased vibration. This is believed to have caused friction and heat between the power shaft and the compressor shaft, resulting in the shafts seizing, accompanied by partial melting.

The investigation board concluded that there was no excessive or incorrect pilot operation. Although normal autorotation landing was difficult due to a sharp drop in main rotor RPM after the engine failure, the investigation determined that the pilot attempted an emergency landing to avoid residential areas until the final moment. The aircraft's final heading was found to have been adjusted about 42 degrees to the left from the normal flight path.

As a follow-up measure, the Army decided to review the retirement schedule of Cobra helicopters in consultation with the Joint Chiefs of Staff. The replacement force, the LAH-1 (Miron) small armed helicopter, will be deployed stably according to an adjusted force integration plan to ensure safety.

Air safety management systems will also be strengthened. By April 2027, the Army plans to transfer the safety management functions and organization of the Army Aviation Command to the Army Headquarters Combat Readiness and Safety Unit. In addition, airfields where helicopters and unmanned aerial vehicles operate together will integrate inspections for both manned and unmanned aircraft.

Advanced training, such as emergency procedures, will be mastered first using flight simulators, and real flight procedures will also be improved. Plans include the additional introduction of simulators by region, updates to maintenance manuals, improvement of aviation facilities, and enhancement of working conditions for rotary wing pilots.

The Army emphasized, "We will faithfully implement safety improvement measures and do our utmost to prevent aviation accidents by supplementing the system for aircraft operation and management."

This content was produced with the assistance of AI translation services.