Accident Overview
On April 7, 2008, at approximately 1230 central daylight time, a Hiller UH-12E helicopter, registered N34SD, was returning to a landing zone after completing an agricultural application when a loud noise was heard accompanied by vibrations. The pilot initiated an autorotation and landed in a nearby field. The helicopter was owned and operated by Texas Air Cargo Inc. The local flight originated from private property located about 5 miles north of Quinton, Oklahoma. Visual meteorological conditions prevailed, and no flight plan was filed for the 14 Code of Federal Regulations Part 137 agricultural application flight.
Pilot Account
The commercial pilot, the sole occupant, reported that the helicopter was cruising at approximately 1,000 feet above ground level when the loud noise occurred. He quickly reduced engine power and began an autorotation. According to the pilot, there was no difficulty controlling the helicopter during the emergency landing, and he was able to perform a normal flare with no associated side angle upon touchdown. The pilot stated that the gearbox had failed, resulting in damage to the helicopter. The pilot reported having 33,000 total flight hours, with 30 hours in the make and model.
Examination
On-scene photographs provided by the pilot showed a fracture of the tail rotor gearbox yoke, twisting of the drive shaft, and damage to the tail rotor blades. The pilot and his employees reported no evidence of a ground strike at the accident site. Another individual reported recovering a tail rotor blade "some distance" from the location of the autorotation. Parts from the helicopter were examined by the NTSB laboratory. A metallurgic examination revealed that all components failed as a result of overload, and no fatigue failures were detected.
Weather Conditions
An automated weather reporting station at McAlister Regional Airport (MLC), approximately 28 nautical miles southeast of the accident site, reported wind from 110 degrees at 11 knots gusting to 14 knots, visibility 10 statute miles, ceiling broken at 6,000 feet, temperature 75 degrees Fahrenheit, dew point 50 degrees Fahrenheit, and barometric pressure of 29.93 inches of Mercury.