Narrative:

First flight of the day for aircraft and crew. I got our dispatch release, noted an MEL item 'GPWS GS deviation mode south inoperative,' crosschecked the MEL/cdl manual, then looked at the aircraft maintenance logbook entry made the previous day deferring it. The aircraft had already flown 3 legs by 2 different crews since being deferred. Everything looked good so I went out to the aircraft to do the receiving checklist and noticed that the GPWS would not test because the circuit breakers had been pulled, and inoperative stickers had been installed over the GPWS annunciators. Our MEL does not state to pull the circuit breakers under any GPWS malfunction requiring a deferral. It is just common sense and is covered in our flight operations manual to deactivate the system to avoid repetitive false warnings. The first crew to fly the aircraft in the deferred condition was apparently advised to pull the circuit breakers by our maintenance control to prevent such a false warning. Here lies the problem: by doing so, the entire GPWS is now deactivated. We have no means of selectively segregating specific modes of the system. This leaves us with 2 possible solutions to deal with this specific MEL: 1) do not deactivate the system (contrary to our flight operations manual) and be faced with a false GPWS warning at 200 ft on GS altitude (as per maintenance logbook write- up), or 2) deactivate by pulling circuit breakers to preclude any cockpit distrs at low altitude. The choice seems clear, however, choice #2 will, technically speaking, change the MEL to read 'GPWS inoperative' and change from category B to category a. I flew the aircraft 2 legs without fully realizing (remembering) that our paperwork reflected only the GS portion inoperative, while in fact, the entire system was now rendered inoperative. In almost 9 yrs in this aircraft with the same airline, I had never seen just the GS mode deferred. To complicate matters further, our aircraft fleet consists of a virtually non standardized group of DC9-10's and DC9-30's of which no 2 cockpits are configured exactly alike, ie, different GPWS's, flight directors, navigation and communication radios, audio panels, radars, switch position, circuit breaker locations, etc. There are many, many circuit breakers that have been pulled and collared in various colors (versus removed) on system that are no longer installed in the aircraft (ACARS, etc) making it very difficult to verify with a glance that all 'usable' circuit breakers are pushed in. I failed twice during this particular trip to notice that only 2 of the 3 GPWS breakers were collared and that 1 was just 'out,' during the 'before start' checklists.

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Original NASA ASRS Text

Title: A DC9-30 WAS DISPATCHED WITH THE GPWS DEFERRED IMPROPERLY AND IN CONFLICT WITH THE MEL.

Narrative: FIRST FLT OF THE DAY FOR ACFT AND CREW. I GOT OUR DISPATCH RELEASE, NOTED AN MEL ITEM 'GPWS GS DEV MODE S INOP,' XCHKED THE MEL/CDL MANUAL, THEN LOOKED AT THE ACFT MAINT LOGBOOK ENTRY MADE THE PREVIOUS DAY DEFERRING IT. THE ACFT HAD ALREADY FLOWN 3 LEGS BY 2 DIFFERENT CREWS SINCE BEING DEFERRED. EVERYTHING LOOKED GOOD SO I WENT OUT TO THE ACFT TO DO THE RECEIVING CHKLIST AND NOTICED THAT THE GPWS WOULD NOT TEST BECAUSE THE CIRCUIT BREAKERS HAD BEEN PULLED, AND INOP STICKERS HAD BEEN INSTALLED OVER THE GPWS ANNUNCIATORS. OUR MEL DOES NOT STATE TO PULL THE CIRCUIT BREAKERS UNDER ANY GPWS MALFUNCTION REQUIRING A DEFERRAL. IT IS JUST COMMON SENSE AND IS COVERED IN OUR FLT OPS MANUAL TO DEACTIVATE THE SYS TO AVOID REPETITIVE FALSE WARNINGS. THE FIRST CREW TO FLY THE ACFT IN THE DEFERRED CONDITION WAS APPARENTLY ADVISED TO PULL THE CIRCUIT BREAKERS BY OUR MAINT CTL TO PREVENT SUCH A FALSE WARNING. HERE LIES THE PROB: BY DOING SO, THE ENTIRE GPWS IS NOW DEACTIVATED. WE HAVE NO MEANS OF SELECTIVELY SEGREGATING SPECIFIC MODES OF THE SYS. THIS LEAVES US WITH 2 POSSIBLE SOLUTIONS TO DEAL WITH THIS SPECIFIC MEL: 1) DO NOT DEACTIVATE THE SYS (CONTRARY TO OUR FLT OPS MANUAL) AND BE FACED WITH A FALSE GPWS WARNING AT 200 FT ON GS ALT (AS PER MAINT LOGBOOK WRITE- UP), OR 2) DEACTIVATE BY PULLING CIRCUIT BREAKERS TO PRECLUDE ANY COCKPIT DISTRS AT LOW ALT. THE CHOICE SEEMS CLR, HOWEVER, CHOICE #2 WILL, TECHNICALLY SPEAKING, CHANGE THE MEL TO READ 'GPWS INOP' AND CHANGE FROM CATEGORY B TO CATEGORY A. I FLEW THE ACFT 2 LEGS WITHOUT FULLY REALIZING (REMEMBERING) THAT OUR PAPERWORK REFLECTED ONLY THE GS PORTION INOP, WHILE IN FACT, THE ENTIRE SYS WAS NOW RENDERED INOP. IN ALMOST 9 YRS IN THIS ACFT WITH THE SAME AIRLINE, I HAD NEVER SEEN JUST THE GS MODE DEFERRED. TO COMPLICATE MATTERS FURTHER, OUR ACFT FLEET CONSISTS OF A VIRTUALLY NON STANDARDIZED GROUP OF DC9-10'S AND DC9-30'S OF WHICH NO 2 COCKPITS ARE CONFIGURED EXACTLY ALIKE, IE, DIFFERENT GPWS'S, FLT DIRECTORS, NAV AND COM RADIOS, AUDIO PANELS, RADARS, SWITCH POS, CIRCUIT BREAKER LOCATIONS, ETC. THERE ARE MANY, MANY CIRCUIT BREAKERS THAT HAVE BEEN PULLED AND COLLARED IN VARIOUS COLORS (VERSUS REMOVED) ON SYS THAT ARE NO LONGER INSTALLED IN THE ACFT (ACARS, ETC) MAKING IT VERY DIFFICULT TO VERIFY WITH A GLANCE THAT ALL 'USABLE' CIRCUIT BREAKERS ARE PUSHED IN. I FAILED TWICE DURING THIS PARTICULAR TRIP TO NOTICE THAT ONLY 2 OF THE 3 GPWS BREAKERS WERE COLLARED AND THAT 1 WAS JUST 'OUT,' DURING THE 'BEFORE START' CHKLISTS.

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.