N2587M

HISTORY OF FLIGHTOn 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. AIRCRAFT INFORMATIONA 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. METEOROLOGICAL INFORMATIONWeather 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. AIRPORT INFORMATIONA 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. WRECKAGE AND IMPACT INFORMATIONThe 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. ADDITIONAL INFORMATIONAutomatic 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 ground stations once per second. ADS-B ground stations record and re-broadcast this data along with additional traffic data collected using legacy radar technology (see figure 2). ADS-B In-equipped aircraft can receive this information, process it through onboard transceivers, and display it on a cockpit display of traffic information (CDTI) screen.

Depending on the configuration of the transceiver and the CDTI, ADS-B In avionics enable aircraft surveillance applications to display traffic and produce visual and aural alerts of predicted collision threats. One example of these applications is the ADS-B traffic advisory system (ATAS). The ATAS application, previously known as traffic situation awareness with alerts, monitors potential traffic conflicts by combining ADS-B tracking data with proximity-prediction algorithms. When it detects a traffic conflict, ATAS sounds an audio alert or “traffic callout.” Conflicting aircraft are also highlighted on cockpit displays when such displays are available in an aircraft. ATAS was designed to operate without excessive nuisance alerts and is the only ADS-B application with an aural-only implementation. Additionally, ATAS was designed to meet FAA Technical Standard Order (TSO) C195b and RTCA Document (DO) No. 317B, Minimum Operational Performance Standards (MOPS) for Aircraft Surveillance Applications System (dated June 17, 2014).

Since January 1, 2020, installation of ADS-B Out equipment is required on all aircraft in the National Airspace System (NAS) operating above 10,000 ft msl and within or above class B and C airspace with certain exceptions. ADS-B Out equipment is not required in the Soldotna area because the airspace is class E and class G. According to 14 CFR 91.225, each person operating an aircraft equipped with ADS-B Out must use transmit mode at all times. ADS-B In is currently not required by the FAA.

An NTSB performance study concluded that if both airplanes had been equipped with ADS-B Out and In, and with CDTI displays capable of ATAS alerts conforming to DO-317B standards, it is possible that both pilots could have been made aware of the presence of the other airplane at least as soon as they were within line-of-sight of each other (say, by the time the Beaver climbed to 500 ft. msl), or by 08:25:01 (about a minute and a half before the collision). Additionally, 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.

FAA Advisory Circular AC 90-48D indicates that the minimum time for a pilot to detect another aircraft, judge a collision course, and take evasive action is about 12.5 seconds. Therefore, it is likely the pilots of both aircraft could have maneuvered to avoid the collision if their aircraft were equipped with ATAS-capable devices conforming to DO371B standards, and these devices were operational.

The FAA recognized the differences between Part 91, Part 121, and Part 135 operations from the perspective of a passenger in the agency’s notice of proposed rulemaking (NPRM) for fractional aircraft ownership. In the NPRM, the FAA stated that aircraft owners flying aboard aircraft that they own or lease “exercise full control over and bear full responsibility for the airworthiness and operation of their aircraft.” In contrast, the FAA stated that passengers who are transported under Parts 121 and 135 “exercise no control over and bear no responsibility for the airworthiness or operation of the aircraft aboard which they are flown” (NARA 2001). As a result, the FAA concluded that the “appropriate level of public safety is provided by…very stringent regulations and oversight under Part 121 and Part 135.”

Additional Previous Related Recommendations

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. (Source: NTSB Aircraft Accident Brief, NTSB/AAR-21/04, “Midair Collision over George Inlet de Havilland DHC-2, N952DB, and de Havilland DHC-3, N959PA, Ketchikan, Alaska, May 13, 2019.”)

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