Accident Summary
On November 9, 2013, at approximately 1245 central standard time, a Eurocopter Deutschland GMBH EC135P1 helicopter, registration N911KB, impacted terrain near Shreveport, Louisiana. The helicopter was operated by Metro Aviation Inc. under 14 CFR Part 91 as a maintenance test flight. Visual meteorological conditions prevailed, and the flight operated without a flight plan. The local flight originated from the company's facility in Shreveport.
Sequence of Events
The helicopter had recently undergone maintenance inspections. The day prior, ground runs were performed to track and balance the rotor system and check the number 2 engine parameters. The crew consisted of a pilot and two mechanics. After preflight and ground runs, the helicopter was refueled, preflighted again, and a hover test was completed in an adjacent field separated by a chain link fence. The hover test was uneventful, and the helicopter landed back at the maintenance facility.
After maintenance personnel made adjustments to the rotor system, another hover test was required. The pilot preflighted the helicopter again, and the crew began the hover test. The helicopter climbed to about 20 feet above ground level and proceeded to overfly the chain link fence. When the helicopter was abeam the fence, the pilot heard a "pop" and the helicopter began a rapid spin. The pilot attempted to regain directional control using the anti-torque pedals but found them ineffective. Unable to regain control, the pilot reduced engine throttle for an autorotation. The helicopter descended, landed, rolled, and came to rest on its right side.
A security surveillance camera recorded part of the accident sequence. The helicopter was observed lifting into a hover, climbing, and rotating counterclockwise about 90 degrees before heading toward the fence. As it exited the camera's field of view, it began a rapid counterclockwise turn.
Post-Accident Examination
An examination by the Federal Aviation Administration, with assistance from the airframe manufacturer, revealed crushing damage on the right, lower, and aft sections of the airframe, consistent with a nose-high, tail-low impact. Cyclic and collective control continuity was established from the controls to the main rotor swashplate. Both anti-torque pedals were found near the wreckage, unattached from their respective attachment levers. None of the attachment hardware was found in the wreckage or vicinity. There was no visible elongation of the pedal bolt holes or the holes on the attachment levers. Tail rotor control continuity was established from the anti-torque pedal levers through to the tail rotor pitch change mechanism. No other preimpact anomalies were detected with the airframe.
The engine Data Collection Unit and Engine Electronic Control were removed and sent to Pratt & Whitney Canada for data download. No fault codes recorded during the accident flight were found.
A teardown of the right engine showed that all power turbine (PT) blades fractured at the airfoil pocket, and the PT shaft showed strong circumferential rubbing. The left engine was examined and found that all PT blades had fractured in overload, with evidence of significant plastic deformation and secondary cracks. The PT shaft showed significant wear consistent with rubbing against an adjacent component, and signatures of frictional heat were detected. The compressor turbine disk displayed circumferential rubbing in the inner bore diameter at the same location where the PT shaft had fractured.
The transmission was examined and revealed no preimpact anomalies.
Maintenance History
A review of the helicopter's logbook found an entry dated October 31, 2013, indicating that a mechanic performed the action "disassemble, inspect, and reassemble tail rotor pedals." According to a statement from the company's director of maintenance, after the accident a search of the maintenance area was conducted. Near the area where the helicopter was previously repaired, a small parts bag was found tied to the tail rotor control cable that had been replaced. Inside the bag were bolts similar to the bolts used to secure the anti-torque pedals.