On July 18, 1998, at 1828 Alaska daylight time, a float equipped Cessna 206 airplane, N7370N, sustained substantial damage when it collided with terrain about 3,000 feet msl at 61 degrees 24.38 minutes North latitude, 148 degrees 14.09 minutes West longitude. The commercial pilot and the three passengers were not injured. The flight was operated under 14 CFR Part 91 as a personal flight to view glaciers. The flight departed from Six Mile Lake Seaplane Base, Anchorage, Alaska, at 1755. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator-in-charge (IIC) during a telephone interview on July 18, 1998, that while cruising at 95 knots, in an up glacier direction about 700 feet above the glacier surface, the airplane began to descend rapidly. The pilot stated he added power, but was unable to arrest the descent before colliding with slightly rising terrain near the glacier's edge. The pilot indicated that he did not attempt to turn because the most favorable landing terrain was ahead of the airplane. He said in the interview, and wrote in his pilot/operator report, that the winds on the surface were flowing down the glacier approximately 15 knots, and the temperature was 55 degrees Fahrenheit. The pilot calculated the airplane's weight to be 3,312 pounds. The Cessna Model U206G rate of climb table shows a maximum rate of climb at 3,300 pounds and 2,000 feet pressure altitude, given a temperature between 0 and 20 degrees C, to be between 915 feet per minute (fpm) and 1,005 fpm.