Narrative:

We were just leveling at 9;000 ft when the master caution light illuminated; accompanied by the #2 rudder hydraulic caution light. The caution light flickered a few times before it came on steadily and remained on. I told my first officer (pilot flying) to slow to 180 KTS. After we identified the problem; I got the emergency/non-normal checklist. Approach handed us off to center. We completed the checklist and decided; since this was a flight control issue; we needed to declare an emergency. We declared the emergency; and told the controller we wished to return to ZZZ. After we declared the emergency; center passed us back to approach. I was communicating with ATC and trying to make sure we were not forgetting anything we needed to do or think about regarding the emergency; so my first officer informed the flight attendant we would be returning to ZZZ for a 'precautionary' emergency landing; and also made a PA to the passengers telling them that we were returning to ZZZ. When he was back up on the radio; I went off and attempted to SELCAL dispatch. I did not get an answer on my first attempt; so I switched to ZZZ operations and had them pass the information along to dispatch. I then came back up on the #1 radio; where we completed the descent approach checklist and discussed the landing in ZZZ. All other hydraulic pressures/quantities and indications were normal; as were all other aspects of the flight. The winds were 060 degrees at 10 KTS when we departed ZZZ; and it was smooth; so we were landing on a 200 ft wide; 10500 ft long runway with minimal crosswind and turbulence. We discussed the increased sensitivity of the rudder; and decided that; barring any other unexpected problems; we would be able to exit the runway normally and taxi to the gate. We executed a normal approach and landing to runway xx and returned to the gate. While reviewing pertinent sections of my fom and pilot operating handbook; I realized an oversight on my part. Even though it is on the normal checklist as the last item after leaving an aircraft after an NTSB reportable event (i.e.; flight control malfunction); I forgot to pull the circuit breaker for the cvr. Even though at the time of the incident we discussed the necessity of declaring an emergency because it was a flight control issue; I failed to remember that was also reportable to the NTSB and I needed to pull the circuit breaker. After speaking to maintenance control next morning; I found out the problem was a broken/defective pressure switch. Replacing the pressure switch repaired the problem.

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Original NASA ASRS Text

Title: DHC-8 flight crew declared an emergency and diverted due to a #2 RUD HYD caution light.

Narrative: We were just leveling at 9;000 FT when the Master Caution light illuminated; accompanied by the #2 Rudder Hydraulic caution light. The caution light flickered a few times before it came on steadily and remained on. I told my First Officer (Pilot flying) to slow to 180 KTS. After we identified the problem; I got the Emergency/Non-Normal checklist. Approach handed us off to Center. We completed the checklist and decided; since this was a flight control issue; we needed to declare an emergency. We declared the emergency; and told the Controller we wished to return to ZZZ. After we declared the emergency; Center passed us back to Approach. I was communicating with ATC and trying to make sure we were not forgetting anything we needed to do or think about regarding the emergency; so my First Officer informed the Flight Attendant we would be returning to ZZZ for a 'Precautionary' emergency landing; and also made a PA to the passengers telling them that we were returning to ZZZ. When he was back up on the radio; I went off and attempted to SELCAL Dispatch. I did not get an answer on my first attempt; so I switched to ZZZ Operations and had them pass the information along to Dispatch. I then came back up on the #1 radio; where we completed the Descent Approach checklist and discussed the landing in ZZZ. All other hydraulic pressures/quantities and indications were normal; as were all other aspects of the flight. The winds were 060 degrees at 10 KTS when we departed ZZZ; and it was smooth; so we were landing on a 200 FT wide; 10500 FT long runway with minimal crosswind and turbulence. We discussed the increased sensitivity of the rudder; and decided that; barring any other unexpected problems; we would be able to exit the runway normally and taxi to the gate. We executed a normal approach and landing to Runway XX and returned to the gate. While reviewing pertinent sections of my FOM and Pilot Operating Handbook; I realized an oversight on my part. Even though it is on the Normal checklist as the last item after leaving an aircraft after an NTSB reportable event (i.e.; flight control malfunction); I forgot to pull the CB for the CVR. Even though at the time of the incident we discussed the necessity of declaring an emergency because it was a flight control issue; I failed to remember that was also reportable to the NTSB and I needed to pull the CB. After speaking to Maintenance Control next morning; I found out the problem was a broken/defective pressure switch. Replacing the pressure switch repaired the problem.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.