Overview
On June 17, 2014, about 1500 central daylight time, a Bell 206B helicopter, registration N536T, made a hard landing at Decatur Municipal Airport (KLUD), Decatur, Texas. The flight instructor and pilot rated student sustained minor injuries, and the helicopter was substantially damaged. The helicopter was registered to MBM Aviation Consultants, Inc. and operated by the Federal Aviation Administration (FAA) under 14 Code of Federal Regulations Part 91 as a training flight. Visual meteorological conditions prevailed, and the flight operated without a flight plan. The flight originated from Fort Worth Alliance Airport (KAFW), Fort Worth, Texas.
The flight was part of the agency's quarterly proficiency program for inspectors. The contract flight instructor initially scheduled was not available, so an FAA flight instructor was assigned. The FAA instructor had flown in the morning with another FAA employee; the accident flight was the student's first with that instructor and the instructor's second flight of the day. The afternoon flight profile was similar to the morning's and was estimated to last about 2.5 hours.
Narrative
According to the instructor and pilot rated student, they were about 2 hours into the proficiency flight, having completed a series of maneuvers including straight-in and 180-degree auto rotations. To complete the flight objectives before returning to KAFW, the instructor planned to demonstrate another 180-degree auto rotation.
The instructor reported that rotor speed was in the mid to low section of the green band at 200 feet at the start of the approach. At the beginning of the flare, he attempted to roll in full throttle but felt resistance and did not restore power in time. He then elected to level the helicopter to avoid a tail-first impact. The helicopter touched down on the asphalt 100 feet short of the fixed distance markers on runway 17.
The pilot rated student stated that on the last 180-degree auto rotation, the instructor was at the controls. At 100 feet on the approach, he noticed the rotor speed was at a minimum and the rate of closure was slow. He felt they would be short, so he called for power and reached for the throttle to confirm it was fully on.
Another helicopter in the airport traffic pattern made a radio call to determine the accident helicopter's position but received no answer. They then observed the helicopter on the ground, upright, just east of runway 17. The main rotor blades were not turning, the tail boom was missing just aft of the horizontal stabilizer, and a debris path began about 400 feet before the 1,000-foot fixed distance markers.
Examination
The NTSB, FAA, and technical representatives from the engine and airframe manufacturers responded to the accident site. Examination of the runway revealed a scar consistent with the tail boom impacting the runway first. The helicopter came to rest upright, partially off the runway, approximately 207 feet from the first impact point. Numerous marks consistent with the helicopter's landing skids were noted between the first scar and the helicopter. The helicopter was resting on its landing skids but leaning to the left. The tail boom had separated just aft of the stabilizer, and the tail rotor gear box was torn from the tail boom. The transmission was tilted aft and had broken free of the driveshaft. Both main rotor blades had impact damage consistent with striking the tail boom and horizontal stabilizer. The NTSB investigator demonstrated free movement of the throttle while the corresponding pointer movement at the Fuel Control Unit (FCU) was witnessed by the engine technical representative.
An examination of the throttle system was conducted on June 19, 2014, by FAA maintenance inspectors in accordance with Bell helicopter maintenance manual (BHT206 MM-1, chapter 76-00-00). No abnormalities were noted in the throttle system, and it met the manufacturer's instructions for continued airworthiness.