What happened
On November 9, 2011, a SAAB 340 was performing a scheduled passenger flight from Warsaw Chopin Airport (EPWR) to Warsaw Modlin Airport (EPWA). After completing engine starts and pre-flight procedures, the crew taxied to runway 29. The configuration for takeoff included flaps at position 0, engine anti-ice turned on, and the Constant Take-Off Torque (CTOT) system set to 108%.
During the takeoff roll, before reaching the V1 decision speed, the crew noticed significant fluctuations on the engine torque (TRQ) indicator. The readings surged to 120% before dropping sharply to approximately 20%. The crew noted that there were no accompanying changes in engine temperature or audible changes in engine sound. Consequently, the commander decided to abort the takeoff. Following instructions from Air Traffic Control, the aircraft taxied to the parking stand, where it was handed over to maintenance personnel.
The investigation
The investigation examined the electrical connections and the performance of the CTOT system. Maintenance personnel discovered that a ground wire for the torque indicator was loose. This looseness was caused by a stripped thread on the screw used to secure the wire to the indicator housing, which had occurred during a previous installation.
Findings
- A loose electrical connection on the torque indicator, caused by a stripped screw thread, led to unstable instrument readings.
- While the loose wire contributed to the initial fluctuations, the investigation identified a progressive failure in the CTOT control panel as the most probable cause. This was evidenced by a similar, more severe incident involving an engine power drop occurring the following day, which was only resolved after the CTOT panel was replaced.
Safety action
- The operator reviewed the incident with flight and maintenance personnel.
- Maintenance procedures were emphasized, specifically regarding the correct tightening of electrical connections and verifying connection security after repairs.
- The necessity of performing special inspections following aborted takeoffs was discussed.
- Training was conducted for both flight and technical crews regarding the principles and procedures for reporting aviation occurrences.