History of Flight
On July 31, 2020, at approximately 0827 Alaska daylight time, a de Havilland DHC-2 (Beaver) airplane, registered N4982U, and a Piper PA-12 airplane, registered N2587M, sustained substantial damage when they collided near Soldotna, Alaska. The pilot of the PA-12 and the pilot and five passengers on the DHC-2 were fatally injured. The DHC-2 was operated as a Title 14 Code of Federal Regulations (CFR) Part 135 on-demand charter flight by High Adventure Charter. The PA-12 was operated as a Title 14 CFR Part 91 personal flight.
The float-equipped DHC-2 departed Longmere Lake, near Soldotna, about 0824, bound for a remote lake on the west side of Cook Inlet to transport passengers to a fishing location. The PA-12 departed Soldotna Airport (PASX) about 0824, bound for Fairbanks, Alaska.
Flight track data showed the DHC-2 traveling northwest at about 78 knots groundspeed, gradually climbing through about 1,175 ft mean sea level (msl) when it crossed the Sterling Highway. The PA-12 was traveling northeast at about 71 knots, at about 1,175 ft msl, north of and parallel to the Sterling Highway. The airplanes collided about 2.5 miles northeast of Soldotna Airport at an altitude of about 1,175 ft msl.
A witness near the accident site reported seeing the DHC-2 traveling west and the PA-12 traveling north. The witness stated that the PA-12 impacted the DHC-2 on the left side of the fuselage toward the back. After the collision, the left wing of the DHC-2 separated, and the airplane entered an uncontrolled descending counterclockwise spiral. The witness did not observe the PA-12 after the collision.
Aircraft Information
A registration card inside the PA-12 identified it as a Piper PA-12 with registration N2587M, which was a valid registration assigned to the pilot according to FAA records. However, the PA-12's exterior registration number was N1904T, and the word "EXPERIMENTAL" was applied inside the lower clam shell door. The FAA registration database showed that N1904T had been reserved by the pilot but was not a valid registration.
The DHC-2 had no traffic awareness equipment installed. The PA-12 was equipped with ADS-B Out and In.
Meteorological Information
Weather observations, cameras, and airborne images taken by passengers on the Beaver within a minute and less than a mile before the collision showed a thin ceiling characterized by high broken-scattered clouds, resulting in a mix of direct sun and shaded conditions. The sun was at about 84° azimuth and about 18° above the horizon, within 20° of the Piper’s track.
Wreckage and Impact Information
The DHC-2 main wreckage was heavily fragmented and located in a wooded residential area, with the fuselage oriented on a heading of about 270° at an elevation of about 240 ft. A debris field about 300 ft long, oriented on about a 327° heading, included the engine, fuselage, wings, vertical stabilizer, and portions of the floats. Dark green paint transfers consistent with the PA-12 were observed on the aft fuselage of the DHC-2.
The PA-12 main wreckage was located about 600 ft east of the DHC-2. The airplane impacted in a near vertical attitude and came to rest at an elevation of about 258 ft. The horizontal stabilizer and one elevator from the DHC-2 were found intertwined in the PA-12 wreckage.
Medical and Pathological Information
FAA records indicated that the PA-12 pilot was denied medical certification in June 2012 due to open-angle glaucoma with visual field loss in both eyes. The pilot requested reconsideration, but the FAA sustained the denial in July 2012. Personal medical records reviewed by the NTSB showed that the pilot's glaucoma was severe and had caused irreversible optic nerve damage and visual field defects in both eyes.
Tests and Research
The NTSB conducted an aircraft performance and cockpit visibility study using ADS-B data for the PA-12, three-dimensional laser scans of exemplar cockpits, passenger photos, radar data for the DHC-2, and wreckage information. The study estimated the location of each airplane in the other pilot’s field of view and recreated possible cockpit display of traffic information (CDTI) data.
At the time of the collision, the sun was behind the DHC-2 pilot and out of view. For the PA-12 pilot, both the sun and the DHC-2 appeared to the east, with the sun's trajectory parallel to and about 20° above the DHC-2’s trajectory. To spot the DHC-2, the PA-12 pilot would have had to look toward the sun.
The cockpit visibility study showed that for 53 seconds before the collision, the Piper would have been unobscured and visible from the DHC-2 cockpit through the left windshield. For the PA-12 pilot, the DHC-2 would have been visible through the right window for 12 seconds, then obscured behind the right wing root, then appeared on the right edge of or obscured by a structural support tube, and finally unobscured and visible in the windshield for 28.3 seconds before impact.
The study also considered 27 potential eye positions for the DHC-2 pilot and found that the PA-12 would have been visible from all positions during the 53-second period. For the PA-12 pilot, visibility of the DHC-2 was sensitive to eye position relative to the right support tube; at some positions, the DHC-2 was temporarily obscured, while at others it was never obscured.
Additional Information
The NTSB noted that ADS-B Out equipment has been required since January 1, 2020, for aircraft operating above 10,000 ft msl and within certain airspace, but not in the Soldotna area, which is Class E and G. ADS-B In is not required by the FAA. An NTSB performance study indicated that if both airplanes had been equipped with ADS-B Out and In with CDTI displays capable of ATAS alerts, both pilots could have been alerted to the other aircraft at least as soon as they were within line-of-sight.
The NTSB also issued safety recommendations regarding common traffic advisory frequency (CTAF) areas in Alaska, based on findings that the airplanes flew converging flightpaths for about 1 minute before the collision.