HISTORY OF FLIGHTOn December 8, 2023, about 1312 Alaska standard time, a Piper PA-18-150 airplane, N1880P, was destroyed when it was involved in an accident near Anchor Point, Alaska. The pilot and passenger were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. A witness near the accident site stated that he heard the airplane’s engine rpm increase, which drew his attention, then looked up and saw the airplane inverted and spinning in a nose-low attitude toward the ground. A vehicle dash-mounted camera recorded about 7 seconds of the airplane’s descent, from about 450 ft above ground level (agl) until the airplane disappeared behind trees (figure 1). The recorded video did not capture the initiating event. The NTSB Vehicle Recorder Laboratory enhanced the video and produced a frame-by-frame flipbook. Review of the video and flipbook revealed the airplane was in an inverted flat spin and was falling vertically at a calculated descent rate of about 4,000 ft per minute (fpm) with no forward momentum throughout the duration of the video. The right wing, empennage, landing gear, and wheel/skis were intact and attached. The left wing’s outboard section was partially separated from the airplane, folded in a V-shape, and remained attached to the fuselage by the lift struts. The left side of the aft fuselage was compromised, deflecting the empennage left of its original position. One propeller blade was positioned up and right, and the other blade was positioned down and left in all frames in which they were visible.

Figure 1. Cropped video frame of accident airplane during descent. A review of data from a Garmin Aera 500 portable GPS receiver located in the wreckage revealed the flight departed King Salmon, Alaska, about 1123 and flew northeast. The pilot climbed to an altitude of about 9,600 ft msl before crossing over the open waters of the Cook Inlet toward Anchor Point. The pilot began a descent about 1304 as the airplane neared the east side of the inlet. The initial descent rate was about 420 fpm and increased to about 1,000 fpm. The descent rate remained steady until the airplane crossed over the shoreline at an altitude of about 4,500 ft msl, about 1311, when the descent rate increased to 4,000 fpm. The National Transportation Safety Board investigatorincharge requested any archived Federal Aviation Administration radar or Automatic Dependent Surveillance–Broadcast (ADSB) data. The initial search did not identify any track information, and a review of the material received showed that it did not capture the accident sequence due to incorrect time and date parameters. A followup request was submitted; however, by that time the radar data had already been purged from the system. The accident airplane was not ADS-B-equipped.

An aerial reconnaissance of the route flown by the accident airplane did not reveal any probable tree impact sites.

Shortly after the accident, the NTSB investigator-in-charge was advised of a radio or phone call that stated, “I need to get this airplane on the ground;” however, the statement could not be substantiated. A review of the pilot and passengers’ phones revealed they did not make any calls around the time of the accident. PERSONNEL INFORMATIONThe pilot’s logbook was not located during the investigation. AIRCRAFT INFORMATIONThe airplane was a high-wing, tailwheel-equipped, two-seat, single-engine airplane. The airframe and engine logbooks were not located during the investigation. AIRPORT INFORMATIONThe airplane was a high-wing, tailwheel-equipped, two-seat, single-engine airplane. The airframe and engine logbooks were not located during the investigation. WRECKAGE AND IMPACT INFORMATIONThe airplane came to rest inverted in an area of low brush and trees. The right wing and right wing’s struts remained attached to the right wing and fuselage. The fuselage was twisted and sustained impact damage; the aft fuselage was penetrated by a tree. The empennage was mostly intact but damaged, and the elevator and rudder remained attached. Control continuity was established between the cockpit flight controls and their respective control surfaces. All major components of the airplane were recovered at the impact site. Further examination revealed that a portion of the left wing’s leading edge skin, about 34 and 67 inches outboard of the fuselage and outboard of the fuel tank, was flattened and fractured into two pieces. There was mechanical tearing damage to the upper portion of the leading edge skin, and an upward semi-circular impression on the lower portion. The leading edge ribs were crushed aft against the forward spar in this area. The fabric skin covering the aluminum leading edge skin in the area of the mechanical damage was torn and ripped, coincident with the leading edge skin damage. Examination of the wing fabric by the NTSB Materials Laboratory revealed at least 6 different gouges, cuts, or scuffs orientated aft and inboard in the black leading edge and portions of the upper (red) and lower (white) painted fabric (figure 2). There was no evidence of transferred material, including tree debris, in these marks. There were two areas that contained silver paint.

Figure 2. A portion of wing fabric showing areas of cuts, gouges, and scuffs. The Smithsonian Institution’s Feather Identification Lab tested swabs from pieces of wing fabric, including the leading edge and portions of the upper and lower painted fabric, for bird residue. It did not find any trace of bird DNA on any items. Examination of the inboard left wing’s structure revealed it was partially attached and rotated down against the fuselage. The forward wing attach point was intact with the bolt installed. The aft wing attach point was intact with the bolt installed, but the wing fitting was fractured from the wing, and the lug was jammed down against the fuselage. The forward spar was fractured about 43 inches outboard of the fuselage. The forward spar was deformed aft and twisted leading edge up inboard of the fracture location. The outboard 2 inches of the forward spar upper cap was twisted leading edge down adjacent to the fracture. The forward spar web was diagonally creased. One of the leading edge ribs was crushed aft against the forward spar. The aft spar was fractured about 56 inches outboard of the fuselage. The aft spar was deformed aft, twisted leading edge up, and then deformed forward between the fuselage and the fracture location.

The forward and aft spars are connected by 3 single-element drag struts. The drag strut in the area of leading edge damage was separated from the spars and remained attached to the outboard wing by one of the diagonal brace wires. The forward end of the drag strut was fractured near the aft end of the forward spar attach bracket and had witness marks consistent with rotation outboard. The aft end of the drag strut was attached to the aft spar attach bracket, but the bolt was pulled through the aft spar web with the bolt intact. The left wing’s area of leading edge damage was just outboard of the left wing fuel tank. The upper skin of the fuel tank was deformed down and there was diagonal buckling between the inboard, forward corner and the outboard, aft corner. There was a distinct impact impression on the forward outboard corner of the fuel tank, consistent with impact with the forward spar upper cap. The diagonal brace tube between the spars and through the tank was pushed aft where the forward spar was deformed aft, and the aft inboard end of the diagonal brace was buckled. All the wing fracture surfaces examined exhibited an angled, dull, grainy appearance consistent with overstress separation. There was no obvious corrosion or evidence of pre-existing fractures. The airplane was equipped with a constant-speed propeller with two composite blades. The propeller hub remained attached to the engine with the spinner and portions of the composite blades still attached. One of the propeller blades was fractured near the shank and was found beneath the nose of the airplane. This propeller blade exhibited a jagged fracture with damage to the leading and trailing edges. The other propeller blade (figure 3) was missing about 7.5 inches of the blade tip, which was not recovered. There was some chordwise scuffing on the cambered side and a linear fracture from leading edge to trailing edge. The metallic leading edge was deformed aft at the fracture location, and the face side of the leading edge was buckled. The Smithsonian Institution’s Feather Identification Lab tested swabs of the camber and face sides of the fractured propeller blade and did not find any trace of bird DNA. Further examination of the propeller blade tip by the NTSB Materials Laboratory revealed the blade tip separated under overstress; no transfer marks were found.

Figure 3. Cambered side of propeller blade with missing tip. Examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Internal engine continuity was confirmed by manually turning the propeller, and thumb compression was observed on all cylinders.