What happened
On November 17, 2018, a UL-A Mirage G-3 aircraft, registration SP-SZUK, was performing a recreational flight near Skawa, Poland. After taking off from a local landing site, the pilot initiated a left turn to depart on course. During the climb, the pilot noticed a change in engine sound and a significant drop in engine speed, falling from 5100 RPM to approximately 3200 RPM.
As the aircraft began to descend, the pilot identified a nearby field to the right as a potential emergency landing site, avoiding tall trees directly ahead. During the approach, the pilot executed a steep right turn and a slip on the right wing at an altitude of approximately 30 meters. While attempting to straighten the aircraft for the landing, the aircraft lost airspeed and stalled at an altitude of about 5 meters, striking the ground on the right wing. The impact caused significant damage to the aircraft and a small electrical fire, which was extinguished by the pilot and a witness. The pilot sustained serious injuries.
The investigation
The PKBWL examined the engine and fuel systems following the accident. While the propeller and engine ignition systems were functional, an inspection of the spark plugs revealed that the second and fourth cylinders were receiving an overly rich fuel-air mixture, evidenced by heavy carbon deposits.
Upon dismantling the carburetors, investigators found clean fuel in the chambers but discovered a critical discrepancy in the left carburetor. The mass of the two floats in the left carburetor was measured at 7.5 grams, exceeding the maximum allowable limit of 7 grams. This weight difference between the floats was identified as a factor in the engine's irregular operation.
Findings
- The primary cause of the accident was a sudden drop in engine RPM shortly after takeoff during the climb phase.
- The aircraft entered a stall during the final moments of the emergency landing due to a loss of airspeed.
- The improper mass of the carburetor floats contributed to the engine malfunction.
- The mountainous terrain and limited available landing sites near the airfield acted as contributing circumstances.
- The pilot was wearing a seatbelt, which helped minimize the severity of the injuries.