Incident Description
On July 11, 2019, at 07:30 UTC, a crew was conducting a training flight under the "Aircraft Training Program for Type or Version SEP(L) Class" task 1. During the demonstration of a static stall, the engine automatically stopped before the aircraft entered the stall phase. The aircraft was climbing at an altitude of 3800 ft and an indicated airspeed of approximately 55 knots. The student pilot ceased the climb and transitioned to descent, increasing airspeed, while the instructor attempted to restart the engine. After turning the ignition key, the instructor successfully restarted the engine and decided to abort the remaining training task. The flight returned to Depułtycze Królewskie Airport (EPCD) at a safe altitude and landed without incident. After landing, the malfunction was recorded in the aircraft technical log.
Cause of the Incident
The cause of the incident was determined to be a discrepancy in carburetor synchronization, inaccurate calibration of spark plugs, and a disturbance of fuel flow resulting from momentary activation of the electric fuel pump.
Contributing Factors
Atmospheric conditions at the altitude may have contributed to carburetor icing, as carburetor heat had not been activated.
Maintenance and Procedural Actions
Additional maintenance work was performed on the involved aircraft (AT-3 R100 SP-CLB) and other AT-3 aircraft operated by the user. The work included a full pneumatic and mechanical resynchronization of the carburetors, inspection of spark plugs, and cleaning of the fuel system. Test flights were conducted in accordance with the maintenance manual, and no further engine irregularities were observed. The aircraft were cleared for further operation.
Following an analysis, the training organization added the following actions to its Standard Operating Procedures (SOP) for static stall demonstrations:
- Activation of carburetor heat;
- Activation of the electric fuel pump at least one minute before performing a climbing flight for the static stall demonstration;
- Increased monitoring of exhaust gas temperatures and cylinder head temperatures.
Carburetor pneumatic and mechanical synchronization tasks were reclassified as "critical tasks" subject to additional inspection.
Safety Recommendations
No additional safety recommendations were formulated by the commission.