HISTORY OF FLIGHT On July 15, 2017, about 0925 Alaska daylight time, a float-equipped Aeronca 15AC airplane, N1370H, sustained substantial damage following a collision with a tree and impact with terrain about 20 miles west of Big Lake, Alaska. The commercial pilot sustained fatal injuries. The airplane was registered to and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions existed, and no flight plan had been filed. The flight departed a remote lake near Big Lake about 0905 destined for Sand Lake, Anchorage, Alaska. According to a family friend, the purpose of the flight was to shuttle several friends from Sand Lake to the pilot's remote recreational cabin. The pilot dropped off the first group of friends and was returning to Sand Lake when the accident occurred. When the airplane failed to arrive at Sand Lake to shuttle the second group of friends, the family friend initiated an aerial search and ultimately found the accident site. The family friend also stated that the pilot liked to fly at a low level over the Yetna River to look for eagle's nests when returning from his recreational cabin. Another family friend said that it was common for the pilot, when returning from his recreational cabin, to fly between 300 and 500 ft above ground level (agl) over the Yetna River to the confluence of the Yetna and Big Susitna Rivers. He would then climb to about 1,100 feet agl for the remainder of the trip to Sand Lake. PERSONNEL INFORMATION The pilot, age 75, held a commercial pilot certificate with ratings for airplane single-engine land and sea and instrument airplane. On May 24, 2017, the pilot applied for "BasicMed,"an alternative to third-class medical certification to fly certain small aircraft, including the accident airplane. Some personal flight records were located for the pilot; however, they were not complete. On his most recent application for a medical certificate, dated June 7, 2013, he indicated that his total aeronautical experience was about 5,892 hours of which 38 hours were in the previous 6 months. AIRCRAFT INFORMATION The airplane was manufactured in 1949. A review of the maintenance records revealed that the most recent annual inspection was completed on September 9, 2016, when the airframe had accumulated 4,659.6 hours total time in service. The airplane was equipped with a Lycoming O-360 engine rated at 180 horsepower at 2,700 rpm. The engine was last overhauled on June 28, 2005 and had accumulated 874.6 hours since overhaul at the most recent annual inspection. METEOROLOGICAL INFORMATION The closest weather observation station to the accident site was Wasilla Airport, Wasilla, Alaska, located about 31 miles east of the accident site. At 0856, Wasilla was reporting, in part, wind calm, visibility 10 statute miles, clouds and ceiling 4,600 ft broken, 6,000 ft overcast, temperature 60°F, dewpoint 51°F, and altimeter 30.01 inches of mercury. WRECKAGE AND IMPACT INFORMATION The accident site was located in an area of brush- and tundra-covered terrain with scattered trees at an elevation of about 50 ft. The initial impact point was marked by a broken tree top, atop an estimated 45-foot-tall cottonwood tree, located about 150 ft from the west bank of the Yetna River. Broken tree branches and paint fragments that matched the color of the airplane were located below the initial impact point. The main wreckage was located northeast along a magnetic heading of about 072° about 450 ft from the initial impact point. The fuselage came to rest inverted. All of the airplane's major components, with the exception of the left wing, were found at the main wreckage site. The severed left wing was located about 160 ft from the initial impact point. A large elliptical impact area was found on the leading edge, about 3 ft outboard of the wing root, with multiple smaller elliptical impact areas outboard to the tip. The left aileron remained attached to its respective attach points and was relatively undamaged. The right wing separated about 3 inches inboard of its rear attach point but remained attached to the fuselage at its forward attach point. Multiple elliptical impact areas were found on the leading edge. The wing's lift strut remained attached at both the fuselage and wing attach points. The right aileron remained attached to its respective attach points but sustained impact damage. The cockpit area was extensively damaged. The engine, firewall, and instrument panel were displaced upward and aft. The throttle control was found in the near full-forward position, and the carburetor heat was in the off position. The horizontal and vertical stabilizer, elevators, and rudder remained attached to the empennage and were relatively free of impact damage. All the primary flight control surfaces were identified at the accident site, and flight control continuity was verified from the cockpit to the elevators and rudder. Aileron control continuity was established from the control column to the overhead aileron bell crank, in the aileron control cables to the wing aileron bell cranks, and in the aileron push-pull tubes. A fracture was observed in the left aileron bell crank; multiple fractures were observed in the overhead aileron bell crank; all fractures were consistent with overload. The engine was examined on August 16, 2017. The engine sustained impact damage to the front, top and underside. No anomalies, contamination, or evidence of malfunction was found in any of the engine accessories. The cylinders, pistons, valve train, crankshaft, and other internal components were all without evidence of anomaly or malfunction. Both magnetos were removed from the engine. When the magneto couplings were rotated, blue sparks were observed at the distributor in rotational order. The propeller remained attached to the engine crankshaft by its attach bolts. Both propeller blades exhibited slight torsional "S" twisting and aft bending. The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. MEDICAL AND PATHOLGOICAL INFORMATION The Alaska State Medical Examiner, Anchorage, Alaska conducted an autopsy of the pilot. The cause of death for the pilot was attributed to multiple blunt force injuries. The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology testing on specimens from the pilot, which were negative for carbon monoxide and ethanol. The toxicology testing revealed 0.039 ug/ml of morphine in the pilot's urine. Morphine is a prescription narcotic used for the treatment of moderate to severe pain. The cutoff for federal workplace testing of urine is 2.000 ug/ml. The level of morphine detected in the pilot's urine was well below this level, and the medication was not detected in his blood.