What happened
On November 9, 2011, a SAAB 340 was performing its third scheduled passenger flight (ACMI) from Warsaw Chopin Airport (EPWR) to Radom (EPWR). The aircraft had a takeoff mass of 11,000 kg, with takeoff speeds set at V1=111kt, Vr=114kt, and V2=116kt. The crew utilized the Constant Take-Off Torque (CTOT) system, which was configured to 96% power.
During the takeoff roll on runway 29, the commander commanded the engines to takeoff power. While the system initially functioned correctly, approximately 3 to 4 seconds after the start of the roll, the First Officer reported a failure. The crew observed that the torque (TRQ) on the number 1 (left) engine surged to approximately 115% and began oscillating before dropping sharply to roughly 30%. This fluctuation was accompanied by a physical yawing motion to the left and a drop in interstage turbine temperature (ITT) to approximately 700°C.
In response to the engine instability, the commander decided to abort the takeoff. The pilot moved the power levers to the ground idle position and initiated braking. The crew notified Air Traffic Control (ATC) of the aborted takeoff and received clearance to taxi via taxiway D4 to apron 4, assisted by a follow-me vehicle.
The investigation
The investigation focused on the performance of the engine power management system during the takeoff phase. Following the incident, the aircraft was inspected by maintenance personnel. Electrical measurements of the engine installation and subsequent ground testing revealed that the CTOT system was malfunctioning due to a delayed engagement of the left engine's torque control.
Findings
- The primary cause of the incident was a malfunction of the CTOT control panel, which resulted in the delayed activation of the torque control system on the left engine.
- The surge and subsequent drop in engine torque caused the aircraft to yaw significantly to the left.
- Maintenance actions included the replacement of the faulty CTOT panel, after which the system functioned normally.
- In accordance with the Minimum Equipment List (MEL), the aircraft was permitted to return to service without an active CTOT system following the repair.