Narrative:

We were in cruise at FL360; about 50 mins into a 1:43 min flight; halfway there between ZZZ1 and ZZZ2. We received a hydraulic 3 hi temperature message on the EICAS and followed the pom checklists from there. We were operating with pump 3A deferred; so with having to turn off pump 3B; we had lost a hydraulic system and some necessary hydraulic services; like landing gear extension; nosewheel steering and inboard ground spoilers. The associated checklists led us to declaring an emergency; diverting to ZZZ and a 12000 ft runway with favorable winds. We tried to ACARS dispatch; and we briefed the flight attendants for an emergency and an unlikely possibility of evacuate/evacuation. We performed an emergency gear extension; and landed without incident with arff standing by. The station was unable to tow us to the gate as we requested. So after the passenger had been bused to the terminal; under maintenance guidance; and after the #3 hydraulic system had cooled; we started up the engines and taxied the aircraft to the ramp. When we received the aircraft for flight we noted that hydraulic pump 3A was deferred. When we read the MEL; it was a little unclr as to how to operate the aircraft in that condition as the usual operation is with 3A on; and 3B automatic to back up 3A or come on during various flight regimes for redundancy. Maintenance said that 3B just stays on in this instance in place of 3A. In reviewing the original write-up that led to hydraulic pump 3A being deferred (hydraulic system 3 had experienced a hi temperature earlier that day already); it appeared that in the previous event the problem may not have been adequately addressed. The write-up said that after pump 3A caused an over-temperature the crew had switched to pump 3B; and though the system had cooled some with the pumps both off; pump 3B was causing the system temperature to rise also. We really have no way to know if this was anything other than an incident that happened to occur. Although it appeared that both pump 3A and pump 3B were causing the temperature in the #3 hydraulic system to rise at the time of the original write-up. It could easily have been that the MEL was correctly assigned and the associated condition deteriorated even faster than anticipated. Or it may have been a misdiagnosed problem that could have been handled more effectively in another way.

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Original NASA ASRS Text

Title: A CRJ900'S #3 HYD SYSTEM HI TEMP EICAS MSG ALERTED IN FLT WITH THE 3A HYD PUMP DEFERRED. AN EMER WAS DECLARED AND THE FLT DIVERTED TO A NEARBY ARPT.

Narrative: WE WERE IN CRUISE AT FL360; ABOUT 50 MINS INTO A 1:43 MIN FLT; HALFWAY THERE BTWN ZZZ1 AND ZZZ2. WE RECEIVED A HYD 3 HI TEMP MESSAGE ON THE EICAS AND FOLLOWED THE POM CHKLISTS FROM THERE. WE WERE OPERATING WITH PUMP 3A DEFERRED; SO WITH HAVING TO TURN OFF PUMP 3B; WE HAD LOST A HYD SYS AND SOME NECESSARY HYD SVCS; LIKE LNDG GEAR EXTENSION; NOSEWHEEL STEERING AND INBOARD GND SPOILERS. THE ASSOCIATED CHKLISTS LED US TO DECLARING AN EMER; DIVERTING TO ZZZ AND A 12000 FT RWY WITH FAVORABLE WINDS. WE TRIED TO ACARS DISPATCH; AND WE BRIEFED THE FLT ATTENDANTS FOR AN EMER AND AN UNLIKELY POSSIBILITY OF EVAC. WE PERFORMED AN EMER GEAR EXTENSION; AND LANDED WITHOUT INCIDENT WITH ARFF STANDING BY. THE STATION WAS UNABLE TO TOW US TO THE GATE AS WE REQUESTED. SO AFTER THE PAX HAD BEEN BUSED TO THE TERMINAL; UNDER MAINT GUIDANCE; AND AFTER THE #3 HYD SYS HAD COOLED; WE STARTED UP THE ENGS AND TAXIED THE ACFT TO THE RAMP. WHEN WE RECEIVED THE ACFT FOR FLT WE NOTED THAT HYD PUMP 3A WAS DEFERRED. WHEN WE READ THE MEL; IT WAS A LITTLE UNCLR AS TO HOW TO OPERATE THE ACFT IN THAT CONDITION AS THE USUAL OP IS WITH 3A ON; AND 3B AUTO TO BACK UP 3A OR COME ON DURING VARIOUS FLT REGIMES FOR REDUNDANCY. MAINT SAID THAT 3B JUST STAYS ON IN THIS INSTANCE IN PLACE OF 3A. IN REVIEWING THE ORIGINAL WRITE-UP THAT LED TO HYD PUMP 3A BEING DEFERRED (HYD SYS 3 HAD EXPERIENCED A HI TEMP EARLIER THAT DAY ALREADY); IT APPEARED THAT IN THE PREVIOUS EVENT THE PROB MAY NOT HAVE BEEN ADEQUATELY ADDRESSED. THE WRITE-UP SAID THAT AFTER PUMP 3A CAUSED AN OVER-TEMP THE CREW HAD SWITCHED TO PUMP 3B; AND THOUGH THE SYS HAD COOLED SOME WITH THE PUMPS BOTH OFF; PUMP 3B WAS CAUSING THE SYS TEMP TO RISE ALSO. WE REALLY HAVE NO WAY TO KNOW IF THIS WAS ANYTHING OTHER THAN AN INCIDENT THAT HAPPENED TO OCCUR. ALTHOUGH IT APPEARED THAT BOTH PUMP 3A AND PUMP 3B WERE CAUSING THE TEMP IN THE #3 HYD SYS TO RISE AT THE TIME OF THE ORIGINAL WRITE-UP. IT COULD EASILY HAVE BEEN THAT THE MEL WAS CORRECTLY ASSIGNED AND THE ASSOCIATED CONDITION DETERIORATED EVEN FASTER THAN ANTICIPATED. OR IT MAY HAVE BEEN A MISDIAGNOSED PROB THAT COULD HAVE BEEN HANDLED MORE EFFECTIVELY IN ANOTHER WAY.

Data retrieved from NASA's ASRS site as of May 2009 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.