What happened
On January 17, 2020, a Saab 340A, registration SP-KPV, was performing a flight from UKKK to EPWA (Warsaw Chopin Airport). During the approach to landing at EPWA, the aircraft was found to be too high relative to the glidepath after passing the Gosit waypoint. Consequently, the crew decided to execute a go-around.
Following the incident, Flight Data Monitor (FDM) analysis revealed that during the initial climb, the propeller shaft torque (TRQ) exceeded the maximum allowable limit of 108% on both engines. The left engine reached 127% TRQ and the right engine reached 119% TRQ. This condition persisted for 30 seconds, significantly exceeding the maximum permissible transient period of 12 seconds. Additionally, at propeller speeds between 900 and 1396 RPM, the torque exceeded the limit of 644 Nm (475 lbf ft), reaching 122% TRQ.
The investigation
The investigation focused on the technical parameters recorded by the FDM and the crew's operational procedures. It was established that the crew failed to activate the Constant Torque on Take-Off (CTOT) system during the go-around procedure. This system is designed to protect the engines by preventing the TRQ from exceeding the crew-set limit of 108%.
Due to the exceedance, the aircraft was withdrawn from service pending engine replacements. The removed engines were scheduled for inspection according to the EMM CT7 maintenance documentation. Furthermore, a non-destructive testing (NDT) inspection of the left propeller hub was required due to the high torque levels recorded.