What happened
On August 8, 2006, a Zlin 143L, registration HB-TCD, was performing glider towing operations near Münster, Switzerland. During the third flight of the day, the pilot noted a decrease in climb performance compared to previous sorties. While on final approach to runway 05 at Münster airfield, the pilot attempted to increase power, but the engine sputtered and failed to respond effectively.
Unable to reach the runway, the pilot attempted an emergency landing in an open, unwooded area near Löuwene. During the descent, the aircraft's stall warning activated. The aircraft struck the edge of a stream embankment, causing the left landing gear to collapse and the left wing to buckle. The pilot sustained serious injuries.
The investigation
Investigators examined the engine and carburetor of the aircraft to determine the cause of the power loss. Upon disassembly of the carburetor, a broken metal rib fragment was discovered lodged within the Venturi channel. This fragment had originated from the interior of the right heat exchanger housing.
Technical analysis of the heat exchanger revealed that the component's internal ribs were prone to failure. Significant wear marks caused by vibrations were found on the external casing of both heat exchanger housings. Furthermore, the mounting holes for the retaining clamps were heavily worn and showed signs of previous repairs using sheet metal. The investigation also confirmed that while there was a significant imbalance in fuel levels between the left and right tanks, there was sufficient fuel remaining in the right tank to prevent fuel exhaustion from being the cause of the engine failure.