FTW04LA198

The 10,100-hour pilot reported that during the flight, he heard a loud bang followed by a subsequent decrease in engine and rotor rpm. The pilot increased the throttle and regained engine and rotor rpm. The pilot added that during a precautionary landing, the engine lost power and the helicopter landed hard in an open field. A witness adjacent to the accident site reported seeing the helicopter strike a power line just prior to landing. Examination of the airframe and engine revealed no anomalies. The reason for the loss of engine power was undetermined.

On July 31, 2004, approximately 1900 central daylight time, a Bell 47-G2 single-engine helicopter, N7892B, was destroyed during a precautionary autorotation landing following a reported loss engine power near La Porte, Texas. The helicopter was registered to a private individual and operated by the pilot. The airline transport rated pilot sustained serious injuries, and the two passengers sustained minor injuries. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight originated from the La Porte Municipal Airport, near La Porte, Texas, approximately 1845.

The 10,100-hour pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that during cruise flight at 600 feet mean seal level (msl), he heard "a loud bang" followed by a subsequent decrease in engine and rotor rpm. The pilot increased the throttle and regained the engine and rotor rpm. After informing his passengers that he was going to make a precautionary landing, he located a field approximately one mile from his position. The pilot further reported that the engine and rotor rpm "remained in the green" until the helicopter was over the field. At an altitude of approximately 50-100 feet, the engine "lost power" followed by the "sudden dip of the nose." The pilot added that he "attempted to level the helicopter before impact" and just prior to touchdown, he "pulled the collective." Subsequently, the helicopter impacted the ground upright, and a post crash fire ensued.

A witness located adjacent to the accident site reported to the Federal Aviation Administration (FAA) inspector, who responded to the site of the accident, that he observed the helicopter strike a power line just prior to landing. Subsequently, the helicopter impacted the ground and "spun around" twice before it came to rest in a field.

Examination of the helicopter by the FAA inspector revealed the fuselage of the helicopter was destroyed by the post-impact fire. The tail rotor gearbox was located approximately 64 yards from the main wreckage. The tail rotor blades remained attached and were bent.

Rotational continuity was established throughout the engine, and both magnetos produced spark on all leads when the engine was rotated by hand. Fuel was observed in the carburetor float bowl and was absent of debris.

On September 1, 2004, the tail rotor output shaft, spiral bevel gear, pinion gear, tail rotor blades, tail rotor drive installation, ninety-degree gearbox, and portions of the tail boom frame assembly were examined under the supervision of the NTSB investigator-in-charge at the engineering laboratories at Bell Helicopter, Hurst, Texas. The examination revealed fractures on the trail rotor driveshaft system, sections of the tail boom, and tail rotor blades, were consistent with overload.

Rotation of the ninety-degree gearbox was not possible due to a bend in the shaft. After sectioning the shaft inboard of the bend, rotational continuity was established. Upon disassembly of the gearbox, it was discovered one of the teeth on the spiral bevel gear had been damaged. The damage was consistent with damage from a pinion tooth edge. No anomalies were found that would have prevented normal operation of the tail rotor gearbox.

The pilot reported that the last annual inspection of the helicopter was completed in February of 2004. At the time of the accident, the helicopter had accumulated approximately 55 hours since the inspection.

At 1850, the automated weather observing system at the Ellington Field Airport (EFD), near Houston, Texas, located six miles southwest of the accident site reported wind from 110 degrees at 3 knots, visibility 10 statute miles, few clouds at 5,000 feet, temperature 89 degrees Fahrenheit, dew point 81 degrees Fahrenheit, and an altimeter setting of 29.88 inches of Mercury.