On April 12, 2015 about 1645 Alaska daylight time, a tailwheel-equipped, Cessna 170B airplane, N4697C, sustained substantial damage following a total loss of engine power shortly after takeoff from an unimproved ski airstrip about 20 miles north of Bettles, Alaska. The certificated commercial pilot and two passengers were not injured. The airplane was registered to a private individual, and operated by the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan had been filed. In an interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 13, 2015, the pilot stated that shortly after takeoff, between about 50 and 70 feet above ground level (agl), a total loss of engine power occurred. After completing the emergency procedures for an engine failure, the pilot lowered the nose of the airplane to find a suitable landing area. When he determined he was unable to reach the desired landing point, he arrested the descent and settled into an area of densely populated birch trees along the side of a river, sustaining substantial damage to the airplane. During a conversation with an NTSB investigator on April 24, 2015, the pilot stated that prior to takeoff, he was unable to check the fuel tanks for contamination using the wing tank fuel drain valves because they were frozen and inoperable. During a post accident aircraft examination, the carburetor was removed from the engine and the float bowl was examined. The float bowl was about 1/2 full with 100LL aviation fuel. The gascollator, electric fuel pump and fuel lines were then drained into a clean, clear container and no contamination was noted. The engine, a Lycoming O-360, was removed with the mounts attached, and transported to Alaskan Aircraft Engines, Inc., Anchorage, Alaska. On June 4 2015, the engine was mounted to a test stand and operated under the direction of an NTSB investigator. The engine ran without any observed anomalies, and produced full factory specified rpm. A drop of about 75 rpm was noted for the left magneto and about 100 rpm for the right magneto. A series of power adjustments from idle to full power were conducted with no hesitation in engine operation noted. The closest weather reporting facility is Bettles Airport, Bettles, approximately 20 miles south of the accident site. At 1553, an aviation routine weather report (METAR) from the Bettles Airport was reporting in part: wind from 150 degrees at 3 knots; sky condition, scattered at 3,000 feet agl, broken at 5,500 feet agl; visibility, 10 statute miles; temperature 19 degrees F; dew point 10 degrees F; barometric pressure 29.53inHg.