ATL02LA044

A Hiller UH-12E collided with the ground during a forced landing. According to the pilot, while executing aerial applications at 15 to 20 feet AGL, he heard a bang and the helicopter began shaking and yawing. The pilot realized he was losing altitude and attempted to slow the descent by using the collective. The helicopter impacted the ground, and caught fire. The pilot exited the helicopter through a hole in the bubble. Examination of the main rotor hub pieces revealed that the fracture at the hub had progressed through the inboard pin hole for the torsion/tension plate set. Six fracture faces were noted in the examination corresponding with the pin hole. Two fracture faces showed discoloration with a distinctive banding pattern and smoothly curved crack arrest marks consistent with fatigue propagation. Examination of the remaining two fractures revealed no evidence of fatigue cracking, but did show some corrosion on the exposed portion of the pin.

On February 11, 2002, at 1706 eastern standard time, a Hiller UH12E, N103HA, registered to and operated by a private owner, under the provisions of Title 14 CFR part 137, collided with the ground during a forced landing in Miami, Florida. The aerial application flight operated under visual flight rules with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The helicopter was substantially damaged, and the pilot was not injured. The flight initially departed Miami, Florida, on February 11, 2002 at 1700.

According to the commercial pilot, while executing aerial applications at 15 to 20 feet AGL, he heard a bang and the helicopter began shaking and yawing. The pilot realized he was losing altitude and attempted to slow the descent by using the collective. The helicopter impacted the ground, and caught fire. The pilot exited the helicopter through a hole in the plexiglass bubble.

Examination of the helicopter showed that the transmission, main rotor, and control rods were broken from the helicopter. The main rotor blades were found lying approximately 150 feet from the accident site, and were bent. The instrument panel, skids, tail rotor drive, main rotor hub, intake, and bubble were all broken, with the main rotor hub broken into two pieces.

The National Transportation Safety Board, Office of Research and Engineering, Materials Laboratory Division, performed metallurgical examination of the main rotor hub pieces. Examination of the main rotor hub pieces revealed that the fracture at the hub had progressed through the inboard pin hole for the torsion/tension plate set. Six fracture faces were noted in the examination corresponding with the pin hole. Two fracture faces showed discoloration with a distinctive banding pattern and smoothly curved crack arrest marks consistent with fatigue propagation. The mating faces of the two discolored fracture faces were found to match the aforementioned fractures. Examination of the remaining two fractures revealed no evidence of fatigue cracking, but did show some corrosion on the exposed portion of the pin.

Main rotor hub history and time in service were not available for review, however, the last reported annual inspection was completed on February 2, 2002, about 22 hours before the accident.