Narrative:

First officer noticed the 'a' system hydraulic quantity at 70%. We watched it continuing to drop. After switching off all hydraulic pumps, I went outside and noticed skydrol flowing from the belly of the aircraft. We wrote it up in the maintenance log and I called maintenance control. Meanwhile the 'a' system quantity continued to drop to a low of 52% while the flow continued and the 'B' system remained at 100%. In talking to maintenance control, he asked if the leak was located between the main gear. I told him I thought it was. He said the leak was due to a xfer valve that was stuck in the wrong position and allowing 'a' system fluid to xfer to 'B' system and then overboard. The fix was simply to reset the valve and replenish the fluid. After returning to the jet, I noticed that I had mistaken the point of the leak. Although centrally located, the leak was actually well forward of the wheelwell and abeam the belly rotating beacon and pouring from the seams and latches of the forward most edges of the left air conditioning pack access panels (the big doors). I called maintenance control again and clarified the point of the leak as I felt that since he was in ZZZ, he needed as much accurate information as I could give him. He said that though much of his previous experience was on 300's from another air carrier, the more forward location of the leak was probably due to the aircraft being a 400. He also indicated that contract maintenance in ZZZ2 had confirmed the xfer valve to be in the wrong position and had reset the valve -- accomplished in the forward east&east compartment. The fluid was refilled, logbook signed off and flight continued to ZZZ3. Upon landing in ZZZ3, after 30 mins of block time, the 'B' system fluid recovered only to 80% -- a loss of 20% in only 30 mins. We switched off the pumps again. On the walkaround, first officer noticed that the fluid was pouring from the same location again. ZZZ3 maintenance hadn't even opened the air conditioning bay access doors when he asked me if we were the jet with the thrust reverser hydraulic leak. I told him that we were the jet with the hydraulic xfer valve problem. He had never heard of that kind of problem but seemed to know of our hydraulic leak and its relationship to the reversers. When he opened the air conditioning panels, he said he saw a few problems. There is apparently a handle that is moved and pinned to deactivate the reversers when maintenance is working on them. That handle was torn off, the entire assembly was missing 2 bolts and the seals were blown thereby gushing skydrol all over the compartment. Since this air conditioning bay access panel (the location from which the most skydrol was coming) was not opened in ZZZ, the real cause of the leak was never detected.

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Original NASA ASRS Text

Title: A B737-400 WAS DISPATCHED FROM ZZZ WITH A 'B' SYS HYD LEAK NOT CORRECTED. ARRIVED IN ZZZ2 WITH 'B' HYDS LOW. FOUND REVERSER LOCKOUT VALVE DAMAGED AND LEAKING.

Narrative: FO NOTICED THE 'A' SYS HYD QUANTITY AT 70%. WE WATCHED IT CONTINUING TO DROP. AFTER SWITCHING OFF ALL HYD PUMPS, I WENT OUTSIDE AND NOTICED SKYDROL FLOWING FROM THE BELLY OF THE ACFT. WE WROTE IT UP IN THE MAINT LOG AND I CALLED MAINT CTL. MEANWHILE THE 'A' SYS QUANTITY CONTINUED TO DROP TO A LOW OF 52% WHILE THE FLOW CONTINUED AND THE 'B' SYS REMAINED AT 100%. IN TALKING TO MAINT CTL, HE ASKED IF THE LEAK WAS LOCATED BTWN THE MAIN GEAR. I TOLD HIM I THOUGHT IT WAS. HE SAID THE LEAK WAS DUE TO A XFER VALVE THAT WAS STUCK IN THE WRONG POS AND ALLOWING 'A' SYS FLUID TO XFER TO 'B' SYS AND THEN OVERBOARD. THE FIX WAS SIMPLY TO RESET THE VALVE AND REPLENISH THE FLUID. AFTER RETURNING TO THE JET, I NOTICED THAT I HAD MISTAKEN THE POINT OF THE LEAK. ALTHOUGH CENTRALLY LOCATED, THE LEAK WAS ACTUALLY WELL FORWARD OF THE WHEELWELL AND ABEAM THE BELLY ROTATING BEACON AND POURING FROM THE SEAMS AND LATCHES OF THE FORWARD MOST EDGES OF THE L AIR CONDITIONING PACK ACCESS PANELS (THE BIG DOORS). I CALLED MAINT CTL AGAIN AND CLARIFIED THE POINT OF THE LEAK AS I FELT THAT SINCE HE WAS IN ZZZ, HE NEEDED AS MUCH ACCURATE INFO AS I COULD GIVE HIM. HE SAID THAT THOUGH MUCH OF HIS PREVIOUS EXPERIENCE WAS ON 300'S FROM ANOTHER ACR, THE MORE FORWARD LOCATION OF THE LEAK WAS PROBABLY DUE TO THE ACFT BEING A 400. HE ALSO INDICATED THAT CONTRACT MAINT IN ZZZ2 HAD CONFIRMED THE XFER VALVE TO BE IN THE WRONG POS AND HAD RESET THE VALVE -- ACCOMPLISHED IN THE FORWARD E&E COMPARTMENT. THE FLUID WAS REFILLED, LOGBOOK SIGNED OFF AND FLT CONTINUED TO ZZZ3. UPON LNDG IN ZZZ3, AFTER 30 MINS OF BLOCK TIME, THE 'B' SYS FLUID RECOVERED ONLY TO 80% -- A LOSS OF 20% IN ONLY 30 MINS. WE SWITCHED OFF THE PUMPS AGAIN. ON THE WALKAROUND, FO NOTICED THAT THE FLUID WAS POURING FROM THE SAME LOCATION AGAIN. ZZZ3 MAINT HADN'T EVEN OPENED THE AIR CONDITIONING BAY ACCESS DOORS WHEN HE ASKED ME IF WE WERE THE JET WITH THE THRUST REVERSER HYD LEAK. I TOLD HIM THAT WE WERE THE JET WITH THE HYD XFER VALVE PROB. HE HAD NEVER HEARD OF THAT KIND OF PROB BUT SEEMED TO KNOW OF OUR HYD LEAK AND ITS RELATIONSHIP TO THE REVERSERS. WHEN HE OPENED THE AIR CONDITIONING PANELS, HE SAID HE SAW A FEW PROBS. THERE IS APPARENTLY A HANDLE THAT IS MOVED AND PINNED TO DEACTIVATE THE REVERSERS WHEN MAINT IS WORKING ON THEM. THAT HANDLE WAS TORN OFF, THE ENTIRE ASSEMBLY WAS MISSING 2 BOLTS AND THE SEALS WERE BLOWN THEREBY GUSHING SKYDROL ALL OVER THE COMPARTMENT. SINCE THIS AIR CONDITIONING BAY ACCESS PANEL (THE LOCATION FROM WHICH THE MOST SKYDROL WAS COMING) WAS NOT OPENED IN ZZZ, THE REAL CAUSE OF THE LEAK WAS NEVER DETECTED.

Data retrieved from NASA's ASRS site as of July 2007 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.