On August 27, 2016, about 1048 Alaska daylight time (AKD), a float-equipped Piper PA-18 airplane, N8998Y, sustained substantial damage after impacting mountainous terrain about 9 miles southwest of Salcha, Alaska. The student pilot, the sole occupant, sustained serious injuries. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Instrument meteorological conditions (IMC) prevailed at the time of the accident and no flight plan had been filed. The flight departed Chena Marina Airport (AK28), Fairbanks, Alaska about 1015 AKD en route to Birch Lake. According to the pilot's flight instructor, the purpose of the flight was for the pilot to attend a business meeting. During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on August 27, the pilot's flight instructor stated that the night before the accident, the accident airplane was experiencing anomalies with the aircraft communications radio. The radio was to be repaired the night before the flight. On the day of the accident, the instructor departed about 10 minutes ahead of the accident pilot in the same direction. Due to low cloud ceilings, the flight instructor returned to Chena Marina. When he landed and turned on his cell phone, he received a voicemail from the accident pilot stating that he had crashed, there was a post-crash fire, and he needed help. The timestamp on the voicemail was 1052. The pilot was rescued by a US Army UH-60 Blackhawk helicopter about 1350 and transported for treatment. A review of archived Federal Aviation Administration air traffic radar and audio recordings depicted the flight instructor's airplane departing AK28 about 1009 and the accident airplane departing about 1015. Immediately after departure, air traffic control queried the accident pilot as to his heading, which he responded with "southeast." Air traffic control queried again for the actual heading, and once more the accident pilot replied "southeast." At 1016, air traffic control asked for his altitude, which he advised was 1,400 ft. At 1030, the pilot made an unauthorized entry into the western edge of the airspace controlled by Eielson Air Force Base. At 1034, the radar data depicts the airplane on a ground track of 123 degrees magnetic and at 1041 the airplane is depicted on a ground track of 117 degrees magnetic. The last radar return attributed to the accident airplane was at 1048 near the location of the accident site. All radio communications from the accident pilot contain static noise consistent with radio interference. The pilot stated on the NTSB Pilot/Operator Aircraft Accident/Incident Report that he departed AK28 about 1015 destined for Birch Lake. While en route, he entered IMC and elected to continue straight ahead and began a descent. While descending, he saw trees through the fog and attempted to climb just prior to impacting the trees. Following the impact, a post-crash fire ensued. The closest weather reporting facility is Eielson Air Force Base, Fairbanks, Alaska, about 16 miles northwest of the accident site. At 1043, a METAR from the Eielson Air Force Base was reporting in part: Wind from 360° at 4 knots; sky condition, overcast at 200 ft; visibility, 3/4 statute miles; temperature, 54° F; dewpoint, 54° F; altimeter, 30.23 inches of mercury.