Bell Helicopter Textron Canada 407 N407KS accident near Renton, Washington

Probable cause

The pilot's failure to maintain helicopter control during takeoff from an unstable landing platform. Contributing to the accident was the operator's inadequate chocking procedures for the wheeled landing platform, which included chocking only two of the platforms four rear wheels and led to the platform's instability.

NTSB analysis

The commercial pilot was conducting a public aircraft flight in the helicopter. The pilot reported that the helicopter was located on an 18-inch-high portable landing platform with eight sets of casters, including four fixed rear casters. The pilot reported that, while he was preparing for departure, he increased the throttle, and the helicopter and platform started to rotate. A witness reported that the helicopter lifted up about 1 foot, shifted forward, and then came down hard on the front of the platform, which caused the platform to rotate. Although the pilot attempted to stop the rotation, he was unsuccessful, and the helicopter began to spin. As the helicopter spun, it tipped rearward, and the tail rotor struck the ground. The helicopter's right landing skid came off the platform. The helicopter and cart stopped rotating, and the pilot shut down the engine.

The operator reported that it had only been chocking two of the four fixed rear casters on the platform, which, they determined postaccident, resulted in the platform being unstable. The pilot likely prematurely lifted off, touched back down on the forward edge of the unstable platform, and subsequently lost helicopter control when the platform began to rotate.

Text from the NTSB. Open the NTSB docket for WPR13TA081 for the full record.