What happened
On July 21, 2018, at the Żar Glider School (EPZR), a scheduled session of glider towing operations was interrupted by an engine malfunction. Prior to the flight, the pilot of the towing Jak 12M aircraft performed a pre-flight inspection and engine run-up. During this test, the pilot noted a drop in engine RPM of over 100 rpm on one magneto, leading him to deem the aircraft unserviceable. However, no entry regarding this malfunction was made in the aircraft's technical logbook.
Approximately 20 minutes later, a second pilot started the engine, warmed it up, and performed a high-RPM spark plug cleaning procedure. Following this, the engine test appeared successful, with RPM drops on both magnetos within normal limits. The Jak 12M then taxied to the SZD-48 Jantar Standard 2 glider for a training flight.
During the initial climb, the aircraft pilot noticed irregular engine performance, characterized by fluctuations of approximately 200 rpm. Due to the lack of climb performance, the pilot initiated a right turn back toward the airfield and signaled for the glider to release. The glider pilot, observing smoke emanating from the aircraft's exhaust manifold and noting the lack of climb, released the glider following the aircraft pilot's wing-wagging signal. Both aircraft subsequently landed safely on the airfield.
The investigation
The PKBWL examined the sequence of engine tests performed by both pilots and reviewed the maintenance documentation. The investigation focused on the discrepancy between the first pilot's findings and the subsequent successful engine test, as well as the physical state of the engine components during the flight.
Findings
- The primary cause of the engine malfunction was spark plug oil fouling.
- The failure to record the initial engine malfunction in the aircraft's technical logbook allowed the second pilot to proceed with the flight under the impression the aircraft was airworthy.
- High ambient temperatures, exceeding 30°C, acted as a contributing factor to the incident.