Incident Description
On 9 November 2011, during a scheduled passenger flight from Wrocław Airport (EPWR) to Warsaw (EPWA), the crew of a SAAB 340 commenced takeoff on runway 29. The commander was the pilot flying, and the first officer was monitoring. Pre-takeoff settings included flaps at 0°, CTOT at 108%, and engine inlet heating on. During the takeoff roll, before reaching V1, the crew observed fluctuations on the torque (TRQ) indicator. The indicator needle reached 120% and then dropped to approximately 20%. No changes in temperature or engine sound were noted. The commander decided to reject the takeoff. After notifying air traffic control, the aircraft taxied to the apron. Following engine shutdown, the aircraft was handed over to maintenance personnel.
Findings
The mechanic who inspected the aircraft found a loose ground wire on the torque indicator's electrical harness. The screw securing the wire had a damaged thread, which had caused the connection to become loose. The damage likely occurred during a previous installation. After re-tightening the screw and performing an engine ground run that showed no anomalies, the aircraft was released for additional flights that day, all of which were completed without further issues.
Upon repeat occurrence the following day during another takeoff, more severe symptoms were observed, including a power reduction on one engine. The CTOT control panel was replaced, after which the problem did not recur.
Probable Cause
The incident could have been caused by a loose ground wire connection on the torque indicator due to improper tightening of the mounting screw, which damaged the thread, making the connection unreliable over time and potentially affecting instrument readings. However, the most probable cause was a developing fault in the CTOT control panel, as evidenced by the recurrence the following day with power loss and the subsequent resolution after panel replacement.
Preventive Actions
The operator was advised to discuss the incident with flight and maintenance personnel, emphasizing proper tightening of electrical connector screws and verifying secure electrical connections after maintenance. Additionally, the need for special inspections after rejected takeoffs was highlighted, and training on incident reporting procedures for flight and technical staff was recommended. No safety recommendations were issued by the commission.