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31.07.2020, 08:27 LT
Soldotna, Alaska, USA
Final Report:
July 31, 2020, midair collision in Alaska
 On
July 31, 2020, about 08:27 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.
Gary Knopp, 67,
a Republican member of the
Alaska House of Representatives, was operating one of the planes that
crashed and was the sole occupant, according to a press release from the
Alaska Department of Public Safety.
The other victims of the crash were
Gregory Bell, 57; David Rogers, 40; Caleb
Hulsey, 26; Heather Hulsey, 25; Mackay Hulsey, 24; and Kirstin Wright,
23, according to the state's Department of Public
Safety.
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 two airplanes 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 DHC-2 was being operated as a Part 135
on-demand 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.
Probable Cause: 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.
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