What happened
On May 8, 2010, at approximately 15:50, a KA-32A helicopter, registration HL9406, operated by HeliKorea Co. Ltd., performed an emergency landing in Buk-ri, Gangwon-do. The aircraft was engaged in a mission to airlift ready-mixed concrete to a high-voltage power line construction site. During takeoff for its eleventh flight of the day, the pilot observed the main gearbox chip warning light illuminating.
In response to the warning, the captain immediately released the external sling load and navigated to a temporary parking ramp located 3.5 km from the lifting site. The engine was shut down upon arrival. While the gearbox oil temperature and pressure remained within normal parameters during the descent, a subsequent inspection revealed significant internal damage. There were no injuries to the crew during the incident.
The investigation
The ARAIB investigation focused on the mechanical integrity of the main gearbox and the rotor brake system. Investigators examined the main gearbox roller bearing, the engine oil cooling fan drive shaft, and the rotor brake components. The inspection identified metal chips exceeding permitted limits within three different chip detectors.
Physical evidence showed that the rotor brake drum had been deformed by friction heat, and several components, including the brake shoe and mounting bracket, had been destroyed or separated. Furthermore, investigators found excessive gaps in the oil cooling fan drive shaft and evidence of rotation-induced damage on the inner walls of the brake drum and bracket.