Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 2500
Human-Machine Interface; Confusion; Communication Breakdown; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft; Human Factors; Procedure
In flight the First Officer informed me that the #2 power lever was causing odd torque indications. Initially when a power lever change was made; the engine would react as if the opposite change occurred. As the power lever was increased; torque decreased approximately 3% before increasing again. As the power lever was decreased; torque increased approximately 3% before decreasing. We landed safely in our filed destination; made a note in the aircraft logbook; and contacted Maintenance Control. The aircraft was met by mechanics; who performed an engine run on the ground. The aircraft was signed off and returned to service.  After the sign off; we readied the aircraft for departure. The logbook showed a corrective action that the problem could not be duplicated. We departed; took off; and in the climb noted the exact problem as before. Maintenance was contacted; and we were advised to return to the departure airport. We landed safely; parked the aircraft; and contacted Maintenance.  We were met at the aircraft by the Mechanic who signed the aircraft off; who immediately apologized. He indicated that the original Mechanic who performed the engine run refused to sign the aircraft off. He also stated that the original Mechanic had indicated a slight split in the power levers; one that was within limitations. Lastly; he informed me that the Mechanic who sat in the right seat of the aircraft during the runup indicated that the engine was acting exactly as we described above. Pilots must be able to always trust that other workers are doing their jobs correctly. Not just maintenance personnel; but occasionally flight attendants; ramp workers; gate agents; and dispatchers. If we weren't able to trust other employee groups; we would never be able to run an efficient operation.  I'm not certain if operational pressures led to an un-airworthy aircraft knowingly receiving a sign off; or if there was a major breakdown in communication between the Mechanic who performed the engine run and the Mechanic who signed the aircraft off.  Either way; a mechanic who refuses to sign an aircraft off should stand by his refusal; and not allow an unsafe airplane to take flight. A mechanic who signs off an airplane should be certain of its airworthiness prior to flight.
A protocol should be implemented for a situation like this where a Mechanic who is signing off an aircraft; but who is not the one who performed the actual work; has to discuss the issue with his immediate Supervisor as well as the Mechanic who is doing/did the work. This would help to eliminate any breakdowns in communication.
A DHC-8 crew detected a momentary torque increase when the throttle was reduced and a momentary decrease with a throttle increase. Maintenance cleared the discrepancy as could not duplicate but the aircraft returned after takeoff for the same behavior.