An ATR72 mechanic failed to reset prop feather and control circuit breakers following a periodic check. When the crew started the engines and attempted to put them into idle feather; the props over torqued.
Synopsis
An ATR72 mechanic failed to reset prop feather and control circuit breakers following a periodic check. When the crew started the engines and attempted to put them into idle feather; the props over torqued.
Narrative
The before start checks were completed and engine start initiated; during engine start on the #2 engine; all parameters were normal except that the ECU (Electronic Control Unit) remained faulted. Performed 1 reset on the ECU and it resumed normal operation. The same process occurred on the start of engine #1: all parameters normal except for the ECU remaining faulted. Reset the ECU and it resumed normal operation. We completed the after start checks and the props were brought out of feather to maximum RPM with normal indications. We taxied out to the de-ice pad; temperature was 0 degrees Celsius and visibility was 1/4 mile in freezing fog. The crew kept their eyes outside the aircraft due to the low visibility. We arrived at the de-ice pad. I set the parking brake and called for the quick turn checklist. I then brought the condition levers to feather. I immediately noticed an abnormal noise and looked at the engine gauges. I saw that the torque was beginning to increase and immediately decided to shutdown the engines. The #2 engine moved into fuel shut off; but the #1 engine was stuck on gate in the feather position. At this point I saw torque moving through 60% and moved my focus onto the condition lever to get it past the gate. Captain was eventually able to move the #1 condition lever into fuel shut off. The result of this was an over-torque of the propellers on engine #1. Several factors contributed to this event: 1) This was the first flight of the week and maintenance had been performed the previous weekend. When that maintenance was performed; the feather control circuit breakers had been pulled for both engines and had failed to be pushed back in.2) The pulled circuit breakers had failed to be identified by the First Officer in his preflight.3) I failed to identify that the LO PITCH lights did not illuminate when I brought the propellers out of feather prior to taxi.4) The condition lever for engine #1 was stuck on the gate at the feather position. It took repeated attempts by both of us until the First Officer was finally able to move it into fuel shut off; at which point too much time had passed allowing an over-torque.
Second reporter narrative
Maintenance had performed a two month check on the aircraft. This check called for pulling the Feather Control and SCU circuit breakers on the engine control overhead circuit breaker panel. Upon completion of the check the circuit breakers were not reset as they should have been. The Captain and I arrived to the aircraft at and completed the acceptance checklist with external power. During the preflight the pulled Feather Control and SCU circuit breakers were not discovered. During initial start both ECU 1 and ECU 2 Faulted. While in Feather both ECUs were reset and parameters appeared to be normal and we continued normal operations. Upon Completion of the after start checklist we taxied to the Deice Ramp located on the other side of the field. RVR at the time was being reported as 1;600 RVR and there was ice on the side windows so both of us were focusing on everything outside of the aircraft. There were no taxi checks completed except for a brake check. Upon reaching the deice pad; the Captain called for the Quick Turn checklist and set the parking brake. While reading the checklist the Captain brought the condition levers to the Feather position. I immediately heard the engines spool up and looked over to see both Torque needles rising. I yelled 'shut it down!' and he was quick to select Fuel Shut off with the #2 condition lever; but was struggling to select Fuel Shut off with the #1 Condition Lever. I eventually reached over grabbed the #1 Condition Lever and selected Fuel Shutoff. We then notified Dispatch and Maintenance control that the #1 Prop may have been over torqued and we opted to have the local FBO tow us back to the ramp just in case the #2 Prop had also been over torqued. The outcome of this incident was a Prop Over Torque of the #1 Engine. This was due to the circuit breakers not being reset after the two month check; my failure to not discover the pulled circuit breakers on the preflight; the crews failure to not detect extinguished LO PITCH lights during the after start and the flight crews failure to shut down the control levers quick enough to prevent the over torque.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.