ANC20LA074

The failure of both pilots to see and avoid the other airplane. Contributing to the accident were (1) the PA-12 pilot’s decision to fly with a known severe vision deficiency that had resulted in denial of his most recent application for medical certification and (2) the Federal Aviation Administration’s absence of a requirement for airborne traffic advisory systems with aural alerting among operators who carry passengers for hire.

Two airplanes, a float-equipped DHC-2 and a PA-12, collided in midair near a local airport shortly after departing from different locations. The DHC-2 was traveling northwest about 1,175 ft mean sea level (msl) and gradually climbing when it crossed a local highway, and the PA-12 was traveling northeast at about 1,175 ft msl north of and parallel to the highway. A witness located near the accident site observed the DHC-2 traveling in a westerly direction and the PA-12 traveling in a northerly direction. He stated that the PA-12 impacted the DHC-2 on the left side of the fuselage toward the back of the airplane. After the collision, he observed what he believed to be the DHC-2's left wing separate, and the airplane entered an uncontrolled, descending counterclockwise spiral before disappearing from view. Both airplanes sustained substantial damage during the collision and impact with terrain. An NTSB cockpit visibility study revealed that for the 53-second period before the collision, the PA-12 would have been unobscured and visible to the DHC-2 pilot through the DHC-2 left windshield. The DHC-2 would have been unobscured and visible to the PA-12 pilot through the PA-12 windshield for 28.3 seconds before the collision. Federal Aviation Administration guidance indicated that 12.5 seconds is the minimum time for a pilot to visually acquire another aircraft, judge a collision course, and take evasive action. Therefore, there was adequate time for both pilots to see and avoid the other airplane. The airplanes flew on converging flightpaths for about 1 minute before the collision. The NTSB determined that, if a common traffic advisory frequency area (CTAF) had been established for the Soldotna area and an FAA requirement had been in place for pilots to communicate their positions when entering the CTAF, the accident might have been avoided. As a result, the NTSB issued recommendations to the FAA to require that pilots report their positions on the designated CTAF when operating in CTAF areas (A-22-4) and create additional dedicated CTAF areas in locations with a high risk for midair collisions (A-22-5). Weather conditions about the time and location of the collision were characterized by a thin ceiling and high broken-scattered clouds resulting in a mix of direct sun and shaded conditions in the general vicinity both airplanes were operating in, which resulted in a complex background for both pilots. Perception of form is determined by a form’s interaction with background features, and the presence of a complex background can cause melding of a form with that background, making it harder to see. The sun was about 84° azimuth and its elevation was about 18° above the horizon, within 20° of the PA-12’s track. Consequently, to spot the DHC-2, the PA-12 pilot would have to be looking toward the sun. The pilot of the PA-12 was denied medical certification in June 2012 due to open-angle glaucoma and had severely impaired peripheral vision. Additionally, even in his central vision where acuity was preserved, he very likely had significantly diminished contrast sensitivity, making areas of light and dark appear less distinct, and colors less vibrant. This likely impaired his ability to resolve lower-contrast features of a visual scene. His severe glaucoma also likely increased his susceptibility to adverse effects of glare. Given the environmental and geometric conditions of this accident, it is likely that the PA-12 pilot’s severe visual impairment reduced his opportunity to identify the Beaver and avert the collision. The DHC2 was being operated as a Part 135 ondemand charter flight, and the PA-12 was operating as a Part 91 personal flight. The DHC-2 had no traffic awareness equipment installed, nor was it required by the Federal Aviation Administration (FAA), but ADS-B Out and In were installed on the PA-12 with avionics capable of providing traffic alerts similar to an airborne traffic advisory (ATAS)-capable device conforming to FAA DO-317B standards. However, it could not be determined if an alert was generated. However, the NTSB believes the lack of a requirement for ADS-B In-based traffic awareness displays for all aircraft conducting Part 135 operations fails to take advantage of the demonstrated benefit of this technology in mitigating the midair collision hazard. In addition, aircraft without ADS-B do not demonstrate the “appropriate level of safety” for passenger-carrying operations conducted under Part 135 regulations. Therefore, the NTSB issued Safety Recommendation A-21-17 to the FAA to require the installation of ADS-B Out- and In-supported airborne traffic advisory systems that include aural and visual alerting functions in all aircraft conducting operations under 14 CFR Part 135. An NTSB performance study concluded that if both aircraft had been equipped with airborne traffic advisory (ATAS)-capable devices conforming to FAA DO-371B standards, the PA-12 pilot would have received an alert 26 seconds before the collision and another alert 9 seconds before the collision. The DHC-2 pilot would have received an alert 26 seconds before the collision and another alert 19 seconds before the collision. It is likely that the pilots of both aircraft could have maneuvered to avoid the collision if their aircraft were equipped with ATAS-capable or similar devices, and these devices were operational.

According to information on file with the FAA, the pilot of the PA-12 was denied medical certification in June 2012 due to open-angle glaucoma with visual field loss in both eyes. Following the denial, the PA-12 pilot requested reconsideration, but the FAA sustained the denial in July 2012. The NTSB reviewed personal medical records from the PA-12 pilot, which showed that his glaucoma was severe and had caused irreversible optic nerve damage and visual field defects in both eyes. A registration card located inside the PA-12 identified the airplane as a Piper PA-12 with a registration number of N2587M. The Federal Aviation Administration's (FAA) registration database revealed that N2587M was a valid registration for a Piper PA-12 assigned to the pilot. However, the PA-12's exterior registration number identified the airplane as N1904T; in addition, the word "EXPERIMENTAL" was applied to the inside of the lower clam shell door. A search of the FAA registration database revealed that the registration number had been reserved by the pilot but was not a valid registration. The DHC2 was being operated as a Part 135 ondemand charter flight, and the PA-12 was operating as a Part 91 personal flight. The DHC-2 had no traffic awareness equipment installed, but ADS-B Out and In were installed on the PA-12. The DHC-2 main wreckage was heavily fragmented and located in a wooded residential area; the fuselage was oriented on a heading of about 270° at an elevation of about 240 ft. A debris field about 300 ft long and 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 wreckage of the PA-12. On July 31, 2020, about 0827 Alaska daylight time, a de Havilland DHC-2 (Beaver) airplane, N4982U, and a Piper PA-12 airplane, N2587M, sustained substantial damage when they were involved in an accident near Soldotna, Alaska. The pilot of the PA-12 and the pilot and the 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. The PA-12 was operated as a Title 14 CFR Part 91 personal flight. The float-equipped DHC-2, operated by High Adventure Charter, departed Longmere Lake, near Soldotna, about 0824 bound for a remote lake on the west side of Cook Inlet. The purpose of the flight was to transport the passengers to a remote fishing location. The PA-12, operated by a private individual, departed Soldotna Airport, Soldotna, Alaska, (PASX) about 0824 bound for Fairbanks, Alaska. Flight track data revealed that the DHC-2 was traveling northwest about 78 knots (kts) groundspeed and gradually climbing through about 1,175 ft mean sea level (msl) when it crossed the Sterling Highway. The PA-12 was traveling northeast about 1,175 ft msl and about 71 kts north of, and parallel to, the Sterling Highway. The airplanes collided about 2.5 miles northeast of the Soldotna airport at an altitude of about 1,175 ft msl. See figure 1 for the airplanes' flight tracks. Figure 1 - Flight track. ADS-B data (N2587M) and ENA/ANX radar data (4982U). A witness located near the accident site observed the DHC-2 traveling in a westerly direction and the PA-12 traveling in a northerly direction. He stated that the PA-12 impacted the DHC-2 on the left side of the fuselage toward the back of the airplane. After the collision, he observed what he believed to be the DHC-2's left wing separate, and the airplane entered an uncontrolled, descending counterclockwise spiral before it disappeared from view. He did not observe the PA-12 following the collision. The NTSB completed an aircraft performance and cockpit visibility study to determine the position and orientation of each airplane in the minutes before the collision using ADS-B data for the PA-12, three-dimensional laser scans of the cockpits of exemplars for both airplanes, passenger photos, radar data for the DHC-2 and wreckage and impact information. This information was then used to estimate the approximate location of each airplane in the other airplane pilot’s field of view and to recreate CDTI data that could have been presented to the pilots. The study determined that, at the time of the collision, for the DHC-2 pilot, the sun would have been behind the DHC-2 pilot’s head and out of view. For the PA-12 pilot, both the sun and the DHC-2 would have appeared to the east of the PA-12, and the trajectory of the sun in the PA-12 pilot’s field of view is parallel to, and about 20° degrees of elevation above, the trajectory of the DHC-2. Consequently, to spot the DHC2, the PA-12 pilot would have to be looking towards the sun. The cockpit visibility study revealed that for the 53-second period before the collision, the Piper would have been unobscured and visible from the DHC-2 pilot through the DHC-2 left windshield. Figure 2 - Recreation of the view from the DHC-2 cockpit at 0826:27 (5.3 seconds before the collision). The location of the PA-12 is indicated by the yellow circle. Regarding whether the PA-12 pilot could have seen the DHC-2, between 0825:39 to just before 0825:51 (12 seconds) the DHC-2 would have been unobscured and visible through the PA-12 right window. The DHC-2 would have then been obscured behind the PA-12 right wing root until about 0825:58. The DHC-2 would then have appeared on the right edge of, or been obscured by, a structural support tube inside the cockpit from about 0825:58 to about 0826:04 (6 seconds). From 08:26:04 to the collision at 08:26:32.3 (28.3 seconds), the DHC-2 would have been unobscured and visible in the PA-12 windshield, just to the left of the support tube. Figure 3 - Recreation of the view from the Piper cockpit at 0826:27 (5.3 seconds before the collision). The location of the DHC-2 is indicated by the yellow circle. The cockpit visibility study also considered whether the geometry of the “blind spots” created by the window supports, and other structures could shift based on the position of the pilot in the cockpit. To determine how this geometry changes as the pilot’s eye position changes (for example, by the pilot leaning in different directions, or by a seat height adjustment), the study considered 27 potential eye positions and evaluated whether the DHC-2 pilot could have seen the PA-12 in any of those positions. The study concluded that the PA-12 would have been unobscured and visible to the DHC-2 pilot for all eye positions considered for the period studied (53 seconds before the collision). The position of the DHC-2 was very sensitive to movements of the PA-12 pilot’s eye position relative to the right support tube behind the PA-12 windshield. At some eye positions, the DHC-2 was temporarily obscured by the support tube, but at others, the tube never obscured the DHC-2. 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 in the general vicinity both airplanes were operating in. The sun was about 84° azimuth and its elevation was about 18° above the horizon, within 20° of the Piper’s track. Automatic Dependent Surveillance-Broadcast (ADS-B) ADS-B uses global navigation satellite system position reports from appropriately equipped aircraft to track aircraft movements. ADS-B Out-equipped aircraft broadcast aircraft position (latitude, longitude, and altitude) and velocity to ADS-B In-equipped aircraft and to ADS-B g