A DHC-8 flight crew; ferrying an aircraft they had just experienced a prop malfunction in (ACN 914943); had the same problem again. They secured the engine; declared an emergency; and continued to destination airport since it was the nearest suitable.
Synopsis
A DHC-8 flight crew; ferrying an aircraft they had just experienced a prop malfunction in (ACN 914943); had the same problem again. They secured the engine; declared an emergency; and continued to destination airport since it was the nearest suitable.
Narrative
We were on a ferry permit; night VMC; expecting that the problem might reoccur. [We] departed [and] had just retracted gear when the prop surged again. We did not want to return to [departure airport] in the dark with mountainous terrain and the shorter runway so we continued to [destination]. We were being handed off to approach about the time check lists were being completed and declared the emergency with them. We landed and taxied to the maintenance hanger. We had been in conversation with Maintenance regarding what we had seen and experienced and I think somehow the reality wasn't understood or interpreted that may have contributed to a misdiagnosis of the problem. A discussion ensued of why the fuel off handle had been pulled as part of our shut down procedure; that may have been causing a hydraulic pump noise when we rotated the prop after the return to [original departure airport]. We also talked with an on-site Mechanic about what we experienced inflight and during run up. There didn't seem to be any question about the idea to ferry. When the surging began the second time we tried shutting off #2 ECU thinking that would fix the problem; but it didn't; so we shut down the engine in the same way as before. We flew to [destination]; considering it a best choice. There is a strong implied statement that it is ok to ferry the aircraft if Maintenance says it is. The weather was in favor of considering it and I focused more on the request than on the details of what all should happen (parts replaced and more detailed inspection by Mechanics) prior to flight. During our 37 min run-up we figured Maintenance had consulted other supervisors and then the Mechanic on-site to come up with this plan. I felt compelled to ferry against better judgment that might have come out had another supervisor been brought in on the conversation. I have an inclination to be more critical in the thought process of troubleshooting both in the cockpit and with maintenance discussions. Taking time to re-evaluate even during the event would've helped.
Second reporter narrative
After our previous emergency landing; maintenance had us runup the airplane and perform various tests (ECU enrichment valve; auto-feather). The we ran the aircraft from idle to takeoff power repeatedly over the course of 30 minutes while in contact with maintenance. We were unable to reproduce the prop malfunction. At this time maintenance told us the most likely cause of the abnormality was the ECU. This problem could likely be solved by selecting the ECU to manual. [The Captain] and I discussed this as a reasonable solution to this problem. We received a ferry permit from maintenance. [The Captain] and I went through a thorough briefing discussing the possibility of a repeat engine shutdown. #2 prop became uncontrollable. Captain maintained positive control of the aircraft while I secured the #2 engine.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.