Incident Overview
On March 12, 2018, a SAAB-340 aircraft operating a flight from EPRZ to UMOO experienced abnormal engine behavior after reaching cruising altitude FL190. The crew noted unusual operation of both engines, characterized by rapid torque (TRQ) fluctuations. When reducing power, torque dropped sharply to minimum values, and when advancing the power levers, torque surged to maximum. These fluctuations also occurred without any movement of the power levers. The captain decided to perform an emergency landing at the nearest suitable airport, EPLB. The landing was conducted safely with the assistance of fire services.
Investigation Findings
The investigation, conducted by the operator under the oversight of Panstwowa Komisja Badania Wypadków Lotniczych, analyzed flight data recorder (FDR) information and crew statements. The analysis identified a malfunction in the CTOT (Constant Torque on Takeoff) system. Further tests checked the 64-inch switch in the Control Quadrant, which determines whether the power lever position allows CTOT activation; the switch operated correctly. The CTOT control panel was then replaced, followed by extended system tests to verify proper operation.
Probable Cause
The probable cause of the incident was determined to be a failure of the CTOT control system.
Preventive Actions
As a preventive measure, the operator briefed all flying personnel on the circumstances and sequence of events. No safety recommendations were formulated by the commission.