Renton, WA, USA
N407KS
BELL HELICOPTER TEXTRON CANADA 407
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.
"***This report was modified on March 3, 2016. Please see the docket for this accident to view the original report.***" On December 28, 2012, about 1015 Pacific standard time (PST), a Bell Helicopter, Model 407, N407KS, made a hard landing during a ground handling operation at Renton Municipal Airport (RNT), Renton, Washington. King County Sheriff's Department was operating the helicopter as a public aircraft. The commercial pilot was not injured; the helicopter sustained substantial damage to the tail rotor system and to the fuselage. The local law enforcement flight was preparing to depart Renton when the accident occurred. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that the helicopter was located on a raised moveable platform that sits about 18 inches off the ground and that the back wheels of the dolly were chocked to prevent movement of the cart. While the pilot was preparing for departure, he increased the throttle, and the helicopter and platform started to rotate. The pilot attempted to stop the rotation by retarding the throttle, but was unsuccessful. The helicopter shifted to the right and the right landing skid came off of the platform. The helicopter stopped spinning and the pilot shutdown all the systems. The helicopter sustained damage to the tail rotor system, fuselage, and the landing gear. A witness reported that he watched the helicopter become airborne and that it lifted up about 1 foot, shifted forward, and then came down hard on the front of the platform, which caused the platform to rotate. He said that the helicopter began to spin, and as it spun, it tipped rearward, and the tail rotor struck the ground. The platform was locally fabricated by the King County Sheriff's Department. It consisted of a platform with 8 sets of casters (total of 16 wheels). The sheriff uses these carts to move aircraft in and out of their hangar. With the exception of the 4 rear fixed casters, the remaining 12 casters swivel. The fixed casters (one wheel in each corner of the cart) were chocked to prevent movement of the platform before the aircraft was operated. Other operators at RNT use similar landing platforms, which use six casters. It was noted that these operators chock all four corner casters to prevent movement of the platform. As a result of this accident and the subsequent investigation, the operator reported that since they had only been chocking the two rear wheels, it did not lead to very good stability of the platform. They have since modified their landing platforms with scissor jacks mounted on all four corners in addition to chocking the wheels.
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.
Source: NTSB Aviation Accident Database
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