Narrative:

Aircraft X arrived. Aircraft was leaking hydraulic fluid from #2 overboard scupper. Troubleshot to leaking #2 engine driven hydraulic pump. Removed and replaced engine driven pump. Bleed #2 system in accordance with what was thought to be correct bleed procedures for #2 engine driven pump replacement. Since ground hydraulic power unit and aircraft jacks are not available we were unable to comply with preferred procedure subtask 29-xx and used back-up procedure as called on in 29-xy dec/mon/05. Performed bleed procedures as provided in subtask 29-xz. Bleed aircraft extensively; aware that the Q400 is air sensitive. Returned aircraft to service. Aircraft flew 12 flight legs without a known hydraulic issue. Ironically; today at approximately XA00 one of my mechanics was installing revision and noted that he installed a new temporary revision for bleeding of the #2 hydraulic system. This being a recent incident as well as our station preparation to start incorporating engineering order (installation of new engine driven hydraulic pumps) in ZZZ1; we started to review the new procedures listed. What we didn't catch yesterday and what was interpreted by one mechanic within our discussion was that the table we used to guide us to subtask 29-xx was actually part of subtask 29-xy. This subtask has a note which requiring a bleed of the system reservoir must only be used as an alternate procedure; until the airplane is in a location where a ground hydraulic power unit can be used to do the bleed procedures. I consulted with the tech office and we decided that the manual is horribly written at best and confusing at worst. Without a clear interpretation we decided to be safe and I wrote an order request to have the system bleed in ZZZ1 when it arrives tomorrow. I notified maintenance control; line planning and submitted this report. The technical office is calling bombardier to gain clarification on the required bleed procedures for the #2 engine driven pump replacement.

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Original NASA ASRS Text

Title: A DHC8-400 ENG DRIVEN HYD PUMP WAS REPLACED BUT INCORRECT BLEED PROCS WERE ACCOMPLISHED. CAUSED BY CONFUSING MAINT MANUAL PROCS AND LACK OF A GND PWRED HYD PUMP.

Narrative: ACFT X ARRIVED. ACFT WAS LEAKING HYD FLUID FROM #2 OVERBOARD SCUPPER. TROUBLESHOT TO LEAKING #2 ENG DRIVEN HYD PUMP. REMOVED AND REPLACED ENG DRIVEN PUMP. BLEED #2 SYS IN ACCORDANCE WITH WHAT WAS THOUGHT TO BE CORRECT BLEED PROCS FOR #2 ENG DRIVEN PUMP REPLACEMENT. SINCE GND HYD PWR UNIT AND ACFT JACKS ARE NOT AVAILABLE WE WERE UNABLE TO COMPLY WITH PREFERRED PROC SUBTASK 29-XX AND USED BACK-UP PROC AS CALLED ON IN 29-XY DEC/MON/05. PERFORMED BLEED PROCS AS PROVIDED IN SUBTASK 29-XZ. BLEED ACFT EXTENSIVELY; AWARE THAT THE Q400 IS AIR SENSITIVE. RETURNED ACFT TO SVC. ACFT FLEW 12 FLT LEGS WITHOUT A KNOWN HYD ISSUE. IRONICALLY; TODAY AT APPROX XA00 ONE OF MY MECHS WAS INSTALLING REVISION AND NOTED THAT HE INSTALLED A NEW TEMPORARY REVISION FOR BLEEDING OF THE #2 HYD SYS. THIS BEING A RECENT INCIDENT AS WELL AS OUR STATION PREPARATION TO START INCORPORATING ENGINEERING ORDER (INSTALLATION OF NEW ENG DRIVEN HYD PUMPS) IN ZZZ1; WE STARTED TO REVIEW THE NEW PROCS LISTED. WHAT WE DIDN'T CATCH YESTERDAY AND WHAT WAS INTERPED BY ONE MECH WITHIN OUR DISCUSSION WAS THAT THE TABLE WE USED TO GUIDE US TO SUBTASK 29-XX WAS ACTUALLY PART OF SUBTASK 29-XY. THIS SUBTASK HAS A NOTE WHICH REQUIRING A BLEED OF THE SYS RESERVOIR MUST ONLY BE USED AS AN ALTERNATE PROC; UNTIL THE AIRPLANE IS IN A LOCATION WHERE A GND HYD PWR UNIT CAN BE USED TO DO THE BLEED PROCS. I CONSULTED WITH THE TECH OFFICE AND WE DECIDED THAT THE MANUAL IS HORRIBLY WRITTEN AT BEST AND CONFUSING AT WORST. WITHOUT A CLR INTERP WE DECIDED TO BE SAFE AND I WROTE AN ORDER REQUEST TO HAVE THE SYS BLEED IN ZZZ1 WHEN IT ARRIVES TOMORROW. I NOTIFIED MAINT CTL; LINE PLANNING AND SUBMITTED THIS RPT. THE TECHNICAL OFFICE IS CALLING BOMBARDIER TO GAIN CLARIFICATION ON THE REQUIRED BLEED PROCS FOR THE #2 ENG DRIVEN PUMP REPLACEMENT.

Data retrieved from NASA's ASRS site as of January 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.