Narrative:

We experienced a complete loss of the #2 hydraulic system quantity in cruise flight. This occurred at FL190 shortly after leveling. We observed the master caution light illuminate; and an associated #2 engine hydraulic pump caution light was illuminated. I looked at the hydraulic gauges and noticed zero #2 hydraulic pressure; and zero #2 hydraulic quantity. Shortly thereafter; the #2 rud hydraulic; rud press; and rud full press caution lights also illuminated. I instructed the pilot flying to remain below 200 KIAS. I then ran the #2 hydraulic system failure checklist with a quantity of zero. I then contacted my dispatcher; and we agreed to return to the departure airport. I declared an emergency with ATC; and we received our new clearance to return to the departure airport. At this time; I spoke to the flight attendant and informed her of our condition; and that we'd be returning to the departure airport. I told her it would be normal landing; but the airfield rescue and fire fighters (arff) vehicles would be escorting our plane to the gate. I made a PA to the passengers. After all communications were complete; the first officer transferred the flight controls to me so he could review the alternate landing gear extension checklist that he would be performing. I remained pilot flying for the remainder of the flight. We landed uneventfully. Once clear of the runway; we terminated the emergency condition with ATC. The arff vehicles followed us to the gate; found no hazards after engine shutdown; and I told them they could clear. Maintenance informed me there was a blown o-ring on a hydraulic line.

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Original NASA ASRS Text

Title: An 'O' ring on a DHC8-300's Number Two Hydraulic system failed in flight causing the loss of all hydraulic fluid and system pressure so an emergency was declared and the flight returned to the departure airport.

Narrative: We experienced a complete loss of the #2 hydraulic system quantity in cruise flight. This occurred at FL190 shortly after leveling. We observed the master caution light illuminate; and an associated #2 ENG HYD PUMP caution light was illuminated. I looked at the hydraulic gauges and noticed zero #2 hydraulic pressure; and zero #2 hydraulic quantity. Shortly thereafter; the #2 RUD HYD; RUD PRESS; and RUD FULL PRESS caution lights also illuminated. I instructed the pilot flying to remain below 200 KIAS. I then ran the #2 HYDRAULIC SYSTEM FAILURE CHECKLIST with a quantity of zero. I then contacted my Dispatcher; and we agreed to return to the departure airport. I declared an emergency with ATC; and we received our new clearance to return to the departure airport. At this time; I spoke to the Flight Attendant and informed her of our condition; and that we'd be returning to the departure airport. I told her it would be normal landing; but the Airfield Rescue and Fire Fighters (ARFF) vehicles would be escorting our plane to the gate. I made a PA to the passengers. After all communications were complete; the First Officer transferred the flight controls to me so he could review the ALTERNATE LANDING GEAR EXTENSION checklist that he would be performing. I remained pilot flying for the remainder of the flight. We landed uneventfully. Once clear of the runway; we terminated the Emergency condition with ATC. The ARFF vehicles followed us to the gate; found no hazards after engine shutdown; and I told them they could clear. Maintenance informed me there was a blown o-ring on a hydraulic line.

Data retrieved from NASA's ASRS site as of July 2013 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.