On July 4, 1993, at 0930 central daylight time, an Aerospatiale SA316B helicopter, N3154Y, impacted the ground near Snyder, Texas, while maneuvering with an external load. The commercial pilot received serious injuries and the helicopter sustained substantial damage. The flight was operating under 14 CFR Part 135 distributing seismographic equipment when the accident occurred. Visual meteorological conditions prevailed and no flight plan was filed. Interviews with the operator and pilot revealed the aircraft and pilot had been operating in the Snyder area for the previous week. On the morning of the accident, which was the first flight of the day, the pilot had positioned the helicopter at the staging area where a 50 foot longline was utilized to support an external load which was comprised of a carousel hooked with six 200 pound bags of equipment. The helicopter was equipped so that the pilot could release the entire load or release individual bags. The intent was to place bags along a grid area running to the south. The pilot had released the first bag of equipment and was maneuvering when the accident occurred. The pilot had no recall of the accident. The enclosed pilot/operator report indicates that a 270 degree left turn occurred and the helicopter descended into the ground with the carousel and remaining bags attached. The operation was conducted north to south. According to witnesses, weather at the time was winds of greater than 25 knots from the south and a temperature of 95 degrees at the site. Recorded weather at Lubbock provided milder conditions. Accident site elevation was approximately 2,300 feet. At the above temperature, the density altitude was approximately 5,000 feet and the aircraft load following the first drop was 1,000 pounds. Computed weight and balance provided information that the helicopter was approximately 400 pounds below its maximum certified gross weight at the time of the accident. Following impact, the wreckage came to rest on a heading of 270 degrees. The airframe, main rotor, tail rotor, and engine sustained damage. The wreckage was removed to the facilities of Roberts Aircraft in Fort Collins, Colorado. Examination of the wreckage occurred at that facility. The examination provided no evidence of preimpact failure or malfunction.