Dash 8 Flight Crew is dispatched with the Beta Lockout deactivated due to a log book write up for fluctuating torque on the number 1 engine. Problem reoccurs after takeoff and flight returns to departure airport.
Synopsis
Dash 8 Flight Crew is dispatched with the Beta Lockout deactivated due to a log book write up for fluctuating torque on the number 1 engine. Problem reoccurs after takeoff and flight returns to departure airport.
Narrative
Maintenance met us at the aircraft and we discovered the aircraft had an open write-up for low prop RPM and fluctuation during takeoff/climbout. It was noted that once the condition levers were brought back to 1050; the fluctuation stopped. Maintenance performed the Beta Lockout Deactivation Procedure; and we then started the engines and cooperated with maintenance to perform the Warning Horn Operational Verification as outlined in the MEL. Once this was completed; maintenance signed off the aircraft; we boarded and departed the gate. Upon taking the runway; the Captain (pilot flying) held the brakes and advanced the power levers then commenced the takeoff roll. Throughout the takeoff roll; the #1 prop RPM was reading approximately 1186 while #2 was around 1208. Both torque indications were steady and within limits. After rotation; the #1 torque began to fluctuate between 74% and 90%. #1 prop RPM remained steady; but lower than usual around 1170. We noticed the aircraft yawing slightly back and forth due to differential power. Once we raised the flaps and brought the condition levers back to 1050 for climbout; the torque fluctuation ceased and everything returned to normal. We decided to return as a precaution; since we would not have maximum power available on the #1 engine. I contacted Operations; advised them of our decision to return; and made a PA. We were vectored for a visual approach and landed uneventfully. We deplaned at the gate; and the Captain made another writeup. The maintenance action taken to troubleshoot the problem was ineffective.
Second reporter narrative
Normal takeoff until nose wheel lifted from runway; then slight flux in #1 prop RPM noted (about 1178-1180 RPM) accompanied by flux in torque on #1 engine. Fluctuation increased as time went on; started with about 5% flux and increased to about 18% flux (change in torque from 72-90%) no torque limitations were exceeded. Previous write up stated flux stopped when props were reduced from 1200 RPM. We cleaned the aircraft up as normal; torque flux disappeared when props were brought below approx. 1080 RPM. Completed after takeoff checklist then told Approach we would return to airport. First Officer talked to passengers and Operations to coordinate return. Completed checklists and returned for normal approach and landing. Deactivating the beta lockout system did not fix the problem with the #1 engine prop/torque fluctuations. Original write up stated problem occurred at takeoff power; went away when power was reduced for climb. Tests for beta lockout system after deactivation are conducted with props at MIN and power levers at/below flight idle. Perhaps a full power engine run before maintenance sign-off to check the problem was actually corrected would have been a good idea?
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.