What happened
On September 5, 2012, a PZL-150A Koliber, registration SP-DIM, was performing a training flight at Gotartowice Airport (EPRG) near Rybnik. The flight was being conducted by an instructor and a student pilot as part of a routine training session involving low-level circuits.
After landing and performing a subsequent takeoff from a conveyor belt, the aircraft entered a climb. At an altitude of approximately 20 to 30 meters, while passing over a railway line, the instructor observed a significant drop in engine RPM. In an attempt to maintain airspeed, the student pilot pulled back on the control column. The instructor took control and attempted to maneuver the aircraft away from a large tree crown ahead. However, the right wing struck the tree branches, causing the aircraft to descend rapidly.
The aircraft then struck an overhead power line, which severed the electrical supply to a nearby property, before impacting an asphalt road. The impact caused the cockpit cover to detach and the left landing gear to break off. The aircraft subsequently slid into a roadside ditch and struck a fence. A fire broke out following the impact, resulting in the total destruction of the aircraft.
The investigation
The PKBWL investigation focused on the engine's performance and the mechanical state of the aircraft. Investigators examined the wreckage, the engine, the fuel system, and the electrical installation. While the engine components and magnetos showed damage from the post-crash fire, they did not reveal a mechanical failure that could explain the power loss.
To understand the engine's behavior, the commission conducted a ground experiment using a similar PZL-150A Koliber, registration SP-FRU. The test simulated a scenario where the three-way fuel valve knob was accidentally bumped from the "L" (left tank open) position. The experiment demonstrated that even a slight deviation of the knob could cause fuel pressure to drop when the throttle was fully opened, leading to a progressive loss of power and eventual engine shutdown.
Findings
- The primary cause of the engine power loss was the accidental deflection of the three-way fuel valve knob from the "L" position.
- The position of the valve knob in the cockpit floor makes it susceptible to being bumped by the feet of the crew, particularly during the transfer of controls.
- The reduction in fuel flow caused a lean fuel-air mixture at full throttle, resulting in a progressive loss of engine power and an insufficient climb gradient to clear obstacles.
- The aircraft was controllable until the moment of impact with the ground and obstacles.
- The aircraft was destroyed by mechanical damage and fire.