On September 3, 2010, about 0600 Pacific daylight time, a Bell 47G-5 helicopter, N4427F, was substantially damaged following impact with terrain near Salinas, California. The commercial pilot, the sole occupant, was seriously injured. Gomes Farm Air Service of Salinas, was operating the helicopter under the provisions of Title 14 Code of Federal Regulations Part 91. Instrument meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The repositioning flight had departed the Salinas Municipal Airport (SNS) about 0550, with its destination being an off-airport work site about 3 miles west of SNS. According to a Federal Aviation Administration (FAA) aviation safety inspector who conducted a telephone interview with the pilot shortly after the accident, the pilot stated that he was flying about 50 feet above the ground and was concerned about the power lines that were hidden by the fog. The pilot reported that he then climbed up to about 80 feet above ground level (agl), which put him in the fog, and when he turned on the landing light in an attempt to illuminate the ground references and identify the power lines, it caused a temporary blinding condition that caused him to become disoriented. The pilot stated that he then attempted a 180-degree turn toward the airport, which resulted in a loss of control and impact with the highway pavement. The pilot reported no mechanical problems with the helicopter. In a written report submitted to the National Transportation Safety Board investigator-in-charge (IIC) several days after the accident, the pilot reported that abeam the airport’s control tower at an altitude of about 75 feet mean sea level (msl) and after turning west toward the interstate highway that borders the airport on the west, he could clearly see a [sugar plant] about 2 miles away. The pilot stated that after reaching the interstate highway he climbed to 100 feet msl and remained clear of clouds, with visibility “2 miles plus.” The pilot revealed that when the helicopter was over the interstate highway’s median strip between the north and southbound lanes, visibility began to deteriorate. The pilot reported that at this time he decided to turn around and return to the airport, as well as to descend in an attempt to re-establish visual contact [with ground references]. The pilot stated that during the descent and course reversal the tail section of the helicopter collided with a guard rail on the highway. The helicopter subsequently impacted the highway pavement and came to rest inverted partially in a southbound lane. The helicopter sustained substantial damage to its airframe. A truck driver who was traveling southbound on the interstate highway reported seeing the helicopter approaching her position from the right side; it was moving from side to side. The witness stated that the helicopter subsequently impacted the terrain and rolled over, coming to rest partially inverted. The witness added that the forward visibility at the time of the accident was about 250 feet, and it was also very foggy. At 0546, a special observation was reported by the SNS Automated Surface Observing System (ASOS), which revealed wind calm, visibility 2 ½ miles, mist, overcast clouds at 100 feet, temperature 13 degrees Celsius, dew point 12 degrees Celsius, and an altimeter setting of 29.96 inches of Mercury. At 0553, the SNS ASOS reported wind calm, visibility 2 ½ miles, mist, overcast clouds at 100 feet, temperature 13 degrees Celsius, dew point 12 degrees Celsius, and an altimeter setting of 29.97 inches of Mercury.