Full Report:

On January 31, 2015, about 1305 Alaska standard time, a wheel/ski-equipped Piper PA-18 airplane, N82735, and a ski-equipped Piper PA-18 airplane, N78NR, collided midair near South Hollywood Airport, about 5 miles southwest of Wasilla, Alaska. N82735 was operated by the State of Alaska Department of Public Safety, Alaska State Troopers, Anchorage, Alaska as a visual flight rules (VFR) cross-country public-use flight, under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. N78NR was registered to and operated by the pilot as a VFR cross-country flight under the provisions of Title 14 CFR Part 91. The sole occupants of the airplanes, both certificated commercial pilots, sustained serious injuries. After the collision, both aircraft descended uncontrolled into an area of densely populated birch and spruce trees and sustained substantial damage. Visual meteorological conditions prevailed in the area at the time of the accident. N82735 departed Wasilla Airport about 1300 bound for Beluga, Alaska, and company flight following procedures were in effect. N78NR departed Birchwood Airport, Chugiak, Alaska about 1250 destined for an off-airport landing site near Johnson Creek with no flight plan on file.
During on-scene interviews with the National Transportation Safety Board (NTSB) Investigator-in-Charge (IIC) on February 1, witnesses consistently reported that they observed one Piper PA-18 traveling in a southwesterly heading, and the other Piper PA-18 traveling in a northwesterly direction. One witness on the ground observed both airplanes converge at approximately a 90 degree angle. The witness said that as both airplanes converged, neither airplane changed altitude or direction as they approached each other, and the two subsequently collided.
During an interview with the NTSB IIC on February 1, a pilot-rated witness that was standing on the east end of South Hollywood Airport, who observed the airplanes just after the collision, stated that he recognized the Alaska State Trooper airplane. He said that after the collision the state trooper's airplane entered a spin, and it began a nose low, spiraling descent. As the airplane reached approximately 400 feet above ground level, the airplane recovered from the spin and briefly leveled off. This was followed by an increase in engine noise. The nose of the airplane then pitched abruptly down, and then the engine noise decreased, which was followed by the sound of the airplane impacting the tree-covered terrain. He said that after the midair collision, the other Piper PA-18 appeared to snap roll to the right as the airplane traveled away from his location. He then observed a large portion of that airplane's right wing flutter to the ground, as it entered a near vertical, uncontrolled, spiraling descent.
During a hospital room interview with the NTSB IIC on February 2, the Alaska State Trooper pilot of N82735 stated that after departure from the Wasilla Airport, he climbed the airplane to approximately 1,500 to 2,000 feet MSL, and configured the airplane for cruise flight. While in level cruise flight, traveling in a southwesterly heading, with the sun at his 1130 to 1200 o'clock position, he saw a momentary flash in the upper left corner of his windscreen, which was instantaneously followed by the collision. After the collision his airplane entered an uncontrollable dive, with no elevator control. In a final effort to regain control, he pushed the control stick forward, and he was able to regain limited elevator authority, but the airplane continued to descend, nose low, into the tree-covered terrain. The last thing the trooper pilot remembered was entering the trees.

At the time of the accident, the pilot of N82735 was utilizing a 4 point safety harness. The harness remained secure throughout the impact sequence and was cut by first responders during the extrication of the pilot.
In addition, the pilot was wearing a standard police issued Kevlar protective vest and a David Clark Series K10 helmet. Pieces of the fractured helmet were found in the cockpit area during the wreckage examination.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20150202X20456&AKey=1&RType=Final&IType=FA