What happened
On September 30, 2015, a Bristell UL RG was performing a landing pattern at Olsztyn-Dajtki Airport (EPOD). During the approach to runway 09, at an altitude of approximately 150 meters, the engine began to vibrate significantly. As the pilot attempted to increase power, the vibrations intensified, prompting the decision to shut down the engine and perform an emergency landing.
While the altitude was sufficient for a safe touchdown, the pilot initiated emergency procedures by shutting off the magnetos and the master switch. Because the aircraft utilizes an electric landing gear deployment system, the loss of electrical power prevented the gear from being extended. The aircraft touched down halfway down the runway with the landing gear retracted. The impact caused the aircraft to bounce approximately 0.5 meters into the air before settling and coming to a stop after traveling an additional 200 meters with a slight leftward deviation. Both the pilot and the passenger sustained no injuries and exited the aircraft unaided.
The investigation
Investigators examined the aircraft and found damage to three propeller blades, abrasions to the fuselage, and damage to several rivets on the lower section of the left wing. The transponder antenna and one of the left flap mounting arms were also damaged.
Upon inspecting the landing gear after the aircraft was moved, investigators confirmed that the electric motor and locking mechanisms were functioning correctly, and the gear could be deployed normally. The investigation then focused on the engine malfunction. It was discovered that the throttle for the right carburetor remained stuck at approximately 40% open, unresponsive to cockpit controls. This was caused by a failure in the control linkage, which allowed the throttle to move freely. While the left carburetor throttle responded correctly to cockpit inputs, the imbalance in fuel delivery between the two sides caused the engine to run unevenly and vibrate.
Findings
- The primary cause of the engine instability was a failure of the carburetor control linkage, which created an uneven fuel mixture between the engine cylinders.
- The landing gear remained retracted because the pilot's sequence of emergency actions—specifically turning off the master switch before attempting gear deployment—rendered the electric system inoperable.
- The cause of the linkage failure could not be determined.