Accident Summary
On July 5, 2023, at approximately 1150 Pacific daylight time, an experimental Avia Stroitel AC-5M motor glider (registration N40233) was substantially damaged during an accident near North Plains, Oregon. The private pilot sustained serious injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Report
The pilot stated that after a recent purchase and condition inspection, he intended to perform maneuvers required by his insurance company. The glider was assembled at North Plains Gliderport (1OR4) and underwent a series of towed high-speed taxis. It was then towed for takeoff and released at approximately 3,100 ft mean sea level (MSL). To familiarize himself, the pilot performed a climbing clearing turn to the right and trimmed the glider to maintain 55 knots indicated airspeed (KIAS) on a southeast heading. He conducted several stalls and recovered uneventfully.
While flying straight and level at about 2,500 ft MSL, the pilot deployed and retracted the motor. During a 30° to 45° right turn to the southeast, the pilot felt the airspeed may have been too slow, and the glider immediately entered a clockwise, “very tight spiral dive.” The pilot neutralized the control stick and applied left rudder. After several revolutions, he stopped the rotation and leveled the wings. He reported that the glider was moving at high speed and shaking. He applied gentle back pressure on the stick, heard an audible “bang,” and observed the right wing separate from the fuselage. He opened the canopy, deployed his parachute below 500 ft above ground level (AGL), and made a hard landing.
Aircraft Information
The Avia Stroitel AC-5M is an experimental motor glider. Its logbook showed that a condition inspection was completed one month before the accident, in accordance with manufacturer instructions, finding it safe for operation. The pilot reported the glider’s weight at the time was 627 lbs. The manufacturer’s flight manual listed a stall speed of about 42 KIAS and a never-exceed speed of 120 KIAS. The parachute was last packed in 2016, though it required repacking every 6 months; the pilot noted the previous owner used it only as additional ballast.
Wreckage Examination
The engine and propeller assembly remained attached to the fuselage, forming the main wreckage. The left wing came to rest 130 ft northeast, the empennage 398 ft northeast, and the right wing 446 ft northeast of the main wreckage. The left wing’s aileron sustained impact damage but remained connected to the bellcrank; the right wing’s aileron was undamaged and connected. The wing root and composite spars tapered into corresponding carry-through boxes connected in the aft fuselage. The 70-lb wing panels were anchored by a single cam-actuated spar pin. Photographic evidence showed the right wing’s inboard spar was fracture separated, while the carry-through spar beams remained attached within the box.
Metallurgical Findings
Postaccident examination of the right-wing spar separation revealed the fracture occurred at the outboard side of the reinforced area of the closeout rib. The spar caps were fiber-reinforced composite separated by a wood laminate web. A materials lab found a cream-colored filler between skin layers, with the fracture path varying between interfaces. No evidence of preexisting or progressive fracture (such as arrest lines or rubbing) was observed. The fracture surfaces of the upper cap were mostly rough and fibrous, consistent with tensile overstress, with a small flattened area indicating compression failure. The lower cap also showed tensile overstress features, along with a resin pocket and a wrinkle in fibers. Longitudinal reinforcement layers in the upper cap deviated from the spanwise direction at the fracture.