WPR23LA270 · Sling Aircraft (PTY) Ltd SLING LSA

The accident occurred during takeoff on an instructional flight. The instructor reported that before reaching rotation speed, the airplane felt as if it were sinking to the left as if they had a flat tire. The flight instructor took over control of the airplane, reduced engine power to idle, and applied the hand brake. The airplane then became uncontrollable and veered to the right. He applied corrective control inputs, but the airplane departed the runway, struck an embankment, and sustained substantial damage.

The instructor reported that the inbound landing was uneventful, and the data recorded by the airplane’s primary flight display corroborated this.

Examination revealed that the left main landing gear leg, which was comprised of composite glass fiber layups, was cracked in multiple areas along its length and had delaminated.

Laboratory examination revealed the cracks occurred within the center bulk of fibers parallel to the lamina. Shiny areas consistent with voids and disbonded material, indicative of a manufacturing anomaly, were spread throughout the fracture surfaces. The voids would have affected the structural integrity and allowed cracking to be initiated more easily within the strut. Entrapped contaminants were also found within the strut matrix and in several locations on the fracture surfaces, which was further evidence of cleanliness issues during manufacturing.

Flattened features were also present on the fracture surfaces and were likely caused by repeated contact between the two halves of the strut as the crack progressed, indicating the crack had been present for some time. Similarly, the presence of dirt/debris on the interior surfaces was likely the result of the gap between the fracture surfaces opening during aircraft operation and allowing dirt/debris to enter. Consequently, the flattened features and embedded dirt/debris are consistent with a pre-existing delamination in the strut before the accident flight.

Both the instructor and the student performed preflight procedures, which included checking the landing gear legs for cracks. Both reported that they did not see any damage or anomalies. It could not be determined why they did not see the cracks, but it is possible that the fractures were imperceptible during a preflight examination, when the airplane was not loaded to an extent that the cracks would open and be visible.

A service bulletin had been issued about 10 years before the accident warning of similar cracks in the landing gear caused by an apparent manufacturing defect. However, this bulletin was not applicable to the accident airplane based on its year of manufacture.

Verbatim NTSB analysis and probable cause from the NTSB dataset