20121228027599A

On December 28, 2012, at approximately 1015 pacific standard time, a Bell model 407 helicopter, registration number N407KS, operated by the king county sheriff's department as a 14 CFR part 91 public aircraft, sustained a tail rotor ground strike and hard landing at Renton municipal airport in Renton, Washington. According to the pilot, he was starting the aircraft in preparation for a police mission in woodinville, Washington. The helicopter was located on a movable cart with the rear fixed casters chocked to prevent movement of the cart during aircraft operation. After a normal start process, the pilot began rolling on the engine throttle from idle, not exceeding 32% engine torque, to accelerate the aircraft's rotor system to 100% RPM.at approximately 80% rotor RPM, the movable cart began to rotate in a counter clockwise direction and the pilot felt the helicopter was also moving in a clockwise direction. The pilot's initial response was to reduce the engine throttle to idle to stop the movement of the cart. This action did not arrest the movement of the cart or the helicopter. The pilot then pulled up on the collective control to prevent the helicopter from sliding forward off the cart, with the engine throttle in the idle position. The pilot stated the aircraft did not become airborne, and he only advanced the engine throttle when he raised the collective as the front of the landing gear was coming off the cart. The Renton federal contract tower reported seeing the helicopter approximately 5 to 10 feet off the movable cart in very unusual gyroscopic movements (large variations of pitch, roll, and yaw). The tower also reported hearing the sound of the main rotor oscillating between high and low pitch and RPM.the aircraft came to rest with the right landing gear skid off the cart, orientated almost 180 degrees from its original position on the movable cart. The pilot did not note any pre-existing mechanical issue with the aircraft.FAA personnel inspected the aircraft, and found the following damage:the front landing gear cross tube failed on the left side. The tail rotor sustained damage due to ground contact. The red main rotor blade contacted the right vertical stabilizer on the horizontal stabilizer. The night sun searchlight caused fuselage damage on the right rear of the aircraft. Flight control continuity of the cyclic and collective controls was verified. Tail rotor drive system continuity and tail rotor flight control continuity were also verified. The only deficiency noted during the check of flight control continuity was a small amount of free play with the tail rotor pedal position adjuster. This free play did not appear to affect normal control of the tail rotor system. Annunciator lights were checked statically with the battery energized by a mechanic from northwest helicopters, inc., the company that provides maintenance services to the sheriff's department. The following lights were illuminated during this check:left boost pump, right boost pump, left fuel transfer, right fuel transfer, generator fail, transmission oil pressure, check instruments, hydraulic system, engine out, RPM, and engine overspeed. The fuel quantity indicator read approximately 890 pounds of fuel. The movable cart the helicopter used 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 rear fixed casters, the remaining 6 sets of casters swivel. The fixed casters (one wheel in each corner of the cart) were chocked to prevent movement of the cart before the aircraft was operated. Similar carts used by other operators at the airport use six casters. Note that these operators chock the corner swivel casters to prevent movement of the cart. The aircraft was moved to northwest helicopters, inc.