On August 30, 2002, at 1006 Pacific daylight time, a Sikorsky S-55T, N747A, collided with terrain while attempting a precautionary landing in a dry creek bed in Lytle Creek, California. The helicopter sustained substantial damage and the commercial pilot, the sole occupant, was not injured. The U.S. Forest Service was operating the helicopter as a fire suppression unit under the provisions of 14 CFR Part 133. The flight originated from a temporary helipad about 0830. Visual meteorological conditions prevailed and no flight plan had been filed. The Forest Service reported that the helicopter had been engaged in water bucket support on a fire for about 2 hours. During the last water drop the bucket failed to release the water. Repeated attempts to release the water failed so the pilot decided to return to base and refuel and repair the bucket. The pilot stated that a red hydraulic warning light illuminated and the flight controls became stiff. He began a precautionary approach to an open area. About 10 feet above the ground, the cyclic flight control moved "hard over," which resulted in the nose moving up and to the right. The pilot was unable to regain control before the main rotor blades made contact with a rocky shelf. The helicopter came to rest on its right side. Post crash examination of the wreckage by the Forest Service investigation team did not reveal evidence of ruptured hydraulic lines. They took a sample of hydraulic fluid from the reservoir and stated that it appeared to be severely contaminated. Post crash examination by a laboratory revealed contamination of the hydraulic fluid by water and microbial growth.