Construcciones Aeronauticas Sa CASA-212 N437RA accident near Toksook Bay, Alaska

Probable cause

The flight crew’s inability to adjust/increase power to the right engine during the landing approach due to an in-flight disconnect of the engine power control linkage, resulting in a loss of control of the airplane. Contributing to the accident was the flight crew’s delayed response in feathering the right engine propeller.

NTSB analysis

According to the captain, as the first officer turned the twin-engine turboprop airplane from base leg to final, she advanced the engine power levers to increase engine power, but the right engine did not respond and the airplane yawed to the right. About 500 feet above the ground, the captain said that he took control and initiated a go-around by adding full engine power. As power was increased, the yaw intensified, and the captain said he was unable to maintain altitude. As he called for the first officer to feather the right engine, the stall warning horn sounded and he had to use both hands to maintain control of the airplane. The airplane continued to descend, struck the tundra-covered terrain, and sustained substantial damage to the fuselage, wings, and empennage. The right engine propeller was not feathered at impact. A postaccident inspection revealed that the linkage connecting the cockpit-mounted engine power lever to the right engine propeller pitch control (PPC) was disconnected, and the bolt connecting the linkage to the PPC was missing. Company management reported that the right engine had been changed 237.2 flight hours before the accident, which required the removal and reinstallation of the PPC linkage. Additionally, the airplane had undergone a scheduled maintenance inspection event following the engine change, 114.3 hours before the accident, requiring a functional test of the torque on the bolt that attaches the linkage. The inspection is part of the operator’s approved airworthiness inspection program. Once the PPC linkage disconnected, the flight crew was unable to control the right engine’s thrust, making it difficult for them to maintain control of the airplane during the approach. Since the bolt that connects the PPC linkage to the splined shaft was not found, it is unknown if the bolt failed or if maintenance personnel failed to properly tighten/torque the bolt at installation.

Text from the NTSB. Open the NTSB docket for ANC09LA009 for the full record.