N55XJ

On March 12, 2023, at 1505 Pacific daylight time, an experimental, amateur-built Cassutt M11, N55XJ, was substantially damaged when it was involved in an accident near Castroville, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated he had conducted clearing turns and was performing an aileron roll when the airplane suddenly entered an uncommanded high-g maneuver, and he lost control of the airplane. He was able to release his seat belt and parachute to the ground. The left wing and aileron separated from the airplane before impacting a muddy field.

The aileron is normally connected to a torque tube that runs along the aft side of the rear spar into the fuselage. The torque tube passes through an inboard trailing edge rib at the wing root and an outboard trailing edge rib adjacent to the inboard end of the aileron. The trailing edge rib is made from carbon fiber skins with a foam core. The mostly intact left aileron, attached torque tube, and both trailing edge ribs separated from the wing and the torque tube fractured from the bellcrank in the fuselage.

The intact carbon fiber outboard trailing edge rib remained with the torque tube. There was no apparent damage to the outboard trailing edge rib carbon laminate. The forward halves of the upper and lower flanges and the forward flange of the outboard trailing edge rib were separated cleanly from the wing consistent with an adhesive type failure at the interface between the carbon and adhesive. The aft halves of the upper and lower flanges of the outboard trailing edge rib were separated from the trailing edge skins with a cohesive type failure through the adhesive. The lower flange also had evidence of foam core material in the bond line. There was excess adhesive on the inboard side of the outboard trailing edge rib. In contrast, the inboard trailing edge rib was fractured through the carbon and the remaining upper and lower flanges had portions of the wing structure substrate still attached. There was not a failure in the bond line at the inboard trailing edge rib. There was no damage to the outboard aileron pin. The aileron torque tube was bent aft near its attach point to the aileron.

The left wing separated from the fuselage and remained mostly intact. The upper trailing edge skin was separated from the left wing above the location of the aileron torque tube and was not recovered. The upper trailing edge skin was torn at the forward end, separated along the skin bond at the trailing edge, and fractured through the foam core in the middle. The main spar fractured just outboard of the attach bracket and photos showed fiber tearing and crushing consistent with overload failure.