What happened
During the landing phase of the flight, the pilot attempted to touch down with the landing gear in the retracted position. This occurred after both the auxiliary and normal hydraulic systems failed to extend the gear assembly. As the aircraft type skidded along the runway, the aircraft caught fire.
Prior to the incident, during the takeoff phase, the left inboard main tire had suffered a failure, resulting in a 30-inch section of tread becoming loose. Evidence of impact was found along the landing gear strut and within the wheel well, specifically above the left inboard wheel.
Findings
Investigation of the hydraulic system revealed that the normal and emergency systems both utilize a shared valve body located on the landing gear actuator. A gap was identified between the actuator and the valve body, which allowed red hydraulic fluid to leak when the systems were pressurized.
Technical examination determined that one of the two bolts securing the hydraulic control valve had fractured and separated. This bolt failure was caused by a shear load acting along the longitudinal axis of the actuator, which was consistent with the impact forces generated by the loose tire tread. The loss of the single bolt allowed the control valve to twist, reducing the clamping force and causing the hydraulic pressure to lift the valve and rupture a critical o-ring.
Furthermore, it was noted that the aircraft lacked necessary shielding to protect essential components in the wheel well from tire debris. While regulations require that systems essential to safe flight be protected from the damaging effects of loose tire treads, no shields were installed to protect the hydraulic components in this instance.