Narrative:

Quick change of airplanes in ZZZ and running late. Aircraft was arriving from maintenance. Maintenance doc was not yet current; so I checked the old one and noticed two deferrals. Deferral 1; MEL X and deferral 2; MEL Y. MEL X is for right AC pack inoperative. According to the maintenance doc the reason the pack was inoperative and deferred was because of a noticeable smell in the aircraft with the pack operating. I believe all will agree that this pack was not operating normally. The flight crew operations placard states that the remaining air conditioning pack must operate normally. MEL Y is for left pack automatic temperature control system inoperative. It seemed to me that this pack was not operating normally either; thus not complying with the prior deferral. I called maintenance and asked if either of these deferrals were going to be fixed. They replied 'no; that the reason for the late maintenance doc was because of another minor issue that they were clearing.' I then asked for reassurance that this was a legal deferral since I no longer considered the (left) 'remaining pack' to be operating normally! After several minutes; he came back and stated that he felt that it was a legal deferral. After conferring with the first officer; I called the duty manager. He initially agreed with me that it was probably an illegal deferral. However he then looked at the flight manual and stated that there was no irregular procedure for operating a pack in standby; so therefore he felt that operating a pack in standby must be a normal procedure. His conclusion; the pack is operating normal! I reminded him that the irregular procedures in the flight manual were changed several years ago. Irregular procedures are not intended for dispatch purposes with inoperative/deferred components. They are intended to be used with in-flight irregular procedures. Because of this logic; I stated that he would not find information on 'operating normally' with a pack in standby in the irregular procedures section of the flight manual. If there were such a procedure; it would be under additional procedures; and there is not a flight manual additional procedure for this problem. Additionally; the 'normals' section of the flight manual always refers to operating the packs in 'automatic;' not 'stby!' he then looked under system descriptions and somehow again rationalized this as a normal operation. To his credit; he did not command me to fly the airplane; and stated that he tended to agree with me; but that he felt it was safe and legal to dispatch. After conferring with first officer again and being assured by maintenance and the duty manager that we were deferring properly; we agreed to take the airplane to avoid at the very least an extended delay and more probably a cancellation. Once en route we again discussed the situation and I began to second guess our decision. I know from my work on the MEL re-write committee that the boeing master MEL preamble makes some reference to a MEL card never taking into consideration another inoperative component in another MEL card. In other words; card X (pack inoperative) flight crew operations placard says that the remaining pack must operate normally. I believe that this is the intent; that all components of the pack (ie; pressurization and air conditioning) operate normally. For example; assume that we had no deferrals. En route we have a problem with our left pack automatic temperature controller (which was one of our deferrals Y). Consulting the flight manual irregular procedure for the over temperature problem; we are told to operate the controller in stby and our problem is solved. We are now operating on two packs; one in automatic and one in stby. I believe this is a 'fail-safe' operation. The key point here is that we still have a back-up pack for pressurization and air conditioning if the stby controller should subsequently fail. My point here (and I believe this shows the intent of the MEL) is that we were deferred with the right pack inoperative and the left pack automatic controller inoperative. Now if the left pack stby temperature controller fails; we have no packs and are therefore unpressurized and doing a high dive! I knowthis probably sounds more complicated than it needs be; but remember that while we have time now to write and attempt to understand this report; in reality we were in real time; already late; being constantly bombarded with flight attendants; passenger; gate agents; zone; push crew; and maintenance wanting to know what was going on and when would we be ready to push! I might also add that this is only my 2ND day using the new maintenance doc with approved operations placard information in lieu of the full MEL card. In both of the MEL items referenced above; there is no reference for the flight crew of where the deferred stickers or placards are to be placed. Because of my working knowledge with the MEL re-write at maintenance headquarters a couple of years ago; I knew that one of the stickers in this deferral was missing entirely and the other was not properly placed on the panel. I had to pull down both MEL cards to confirm this information. If the new formatted maintenance doc gives us all the information we need; will the PIC still be held responsible for missing or wrongly placed decals or placard information during a FAA line check? If the answer is yes; then we need more operations placard information or we should still be pulling down entire MEL cards for every deferral.supplemental information from acn 746689: upon reviewing the logbook during the preflight; the captain noticed a possible problem concerning two deferred items that existed concurrently. The defects and corresponding deferrals in question are described below: 1) 1 defect: 'left pack automatic temperature control system(south) inoperative' (MEL reference Y) flight crew directive: a) associated pack standby temperature control system must operate normally 2) 2 defect: 'right air conditioning pack inoperative' (MEL reference# X). Flight crew directive: a) remaining air conditioning pack must operate normally B) maintain associated pack selector in 'off' position for all phases of flight C) advise purser since we were required by the above MEL Y to operate the left pack in the standby mode; we were concerned that we would not satisfy the requirements of MEL X which required the operating pack to operate normally. We discussed what constituted a pack system that 'must operate normally.' we attempted to get clarification from maintenance and the fodm by soliciting their interpretation of what constituted normal pack operation. The mechanic stated that 'the left pack does operate normally; so we are good.' the captain got a similar response from the fodm. We were initially satisfied with their assessment and considered the maintenance status acceptable and within the limitations of the MEL and departed. Once airborne; and after a thorough discussion with the captain; we both agreed that perhaps the left pack should not be considered to be operating normally when required by MEL to operate in standby mode. In retrospect; I now consider our flight as an illegal dispatch due to conflicting requirements of concurrent MEL cards.callback conversation with reporter revealed the following information: reporter states: currently their system of MEL deferrals does not recognize when two mels are concurrently in conflict. In this situation; right pack is inoperative and left pack; with automatic temperature mode control inoperative and only the standby control is functioning. With right pack already inoperative and if the left pack standby temperature also fails; than both packs would be inoperative and cabin would become un-pressurized. The issue of what is a normal operating system needs to be addressed. The boeing master MEL (mmel) preamble appears to make some reference to a MEL card never taking into consideration another inoperative component in another MEL card.

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Original NASA ASRS Text

Title: A B757-200 PLT QUESTIONS MEL AND RELEASE OF ACFT WITH R PACK INOP AND L PACK AUTO TEMP CONTROL INOP. ALSO; ISSUES OF NEW MAINT RELEASE PROCEDURES AND PLACARD POSITIONING.

Narrative: QUICK CHANGE OF AIRPLANES IN ZZZ AND RUNNING LATE. ACFT WAS ARRIVING FROM MAINT. MAINT DOC WAS NOT YET CURRENT; SO I CHECKED THE OLD ONE AND NOTICED TWO DEFERRALS. DEFERRAL 1; MEL X AND DEFERRAL 2; MEL Y. MEL X IS FOR R AC PACK INOP. ACCORDING TO THE MAINT DOC THE REASON THE PACK WAS INOPERATIVE AND DEFERRED WAS BECAUSE OF A NOTICEABLE SMELL IN THE AIRCRAFT WITH THE PACK OPERATING. I BELIEVE ALL WILL AGREE THAT THIS PACK WAS NOT OPERATING NORMALLY. THE FLT CREW OPS PLACARD STATES THAT THE REMAINING AIR CONDITIONING PACK MUST OPERATE NORMALLY. MEL Y IS FOR L PACK AUTO TEMP CONTROL SYSTEM INOPERATIVE. IT SEEMED TO ME THAT THIS PACK WAS NOT OPERATING NORMALLY EITHER; THUS NOT COMPLYING WITH THE PRIOR DEFERRAL. I CALLED MAINT AND ASKED IF EITHER OF THESE DEFERRALS WERE GOING TO BE FIXED. THEY REPLIED 'NO; THAT THE REASON FOR THE LATE MAINT DOC WAS BECAUSE OF ANOTHER MINOR ISSUE THAT THEY WERE CLEARING.' I THEN ASKED FOR REASSURANCE THAT THIS WAS A LEGAL DEFERRAL SINCE I NO LONGER CONSIDERED THE (LEFT) 'REMAINING PACK' TO BE OPERATING NORMALLY! AFTER SEVERAL MINUTES; HE CAME BACK AND STATED THAT HE FELT THAT IT WAS A LEGAL DEFERRAL. AFTER CONFERRING WITH THE FO; I CALLED THE DUTY MANAGER. HE INITIALLY AGREED WITH ME THAT IT WAS PROBABLY AN ILLEGAL DEFERRAL. HOWEVER HE THEN LOOKED AT THE FLT MANUAL AND STATED THAT THERE WAS NO IRREGULAR PROCEDURE FOR OPERATING A PACK IN STANDBY; SO THEREFORE HE FELT THAT OPERATING A PACK IN STANDBY MUST BE A NORMAL PROCEDURE. HIS CONCLUSION; THE PACK IS OPERATING NORMAL! I REMINDED HIM THAT THE IRREGULAR PROCEDURES IN THE FLT MANUAL WERE CHANGED SEVERAL YEARS AGO. IRREGULAR PROCEDURES ARE NOT INTENDED FOR DISPATCH PURPOSES WITH INOPERATIVE/DEFERRED COMPONENTS. THEY ARE INTENDED TO BE USED WITH IN-FLT IRREGULAR PROCEDURES. BECAUSE OF THIS LOGIC; I STATED THAT HE WOULD NOT FIND INFORMATION ON 'OPERATING NORMALLY' WITH A PACK IN STANDBY IN THE IRREGULAR PROCEDURES SECTION OF THE FLT MANUAL. IF THERE WERE SUCH A PROCEDURE; IT WOULD BE UNDER ADDITIONAL PROCEDURES; AND THERE IS NOT A FLT MANUAL ADDITIONAL PROCEDURE FOR THIS PROBLEM. ADDITIONALLY; THE 'NORMALS' SECTION OF THE FLT MANUAL ALWAYS REFERS TO OPERATING THE PACKS IN 'AUTO;' NOT 'STBY!' HE THEN LOOKED UNDER SYSTEM DESCRIPTIONS AND SOMEHOW AGAIN RATIONALIZED THIS AS A NORMAL OPERATION. TO HIS CREDIT; HE DID NOT COMMAND ME TO FLY THE AIRPLANE; AND STATED THAT HE TENDED TO AGREE WITH ME; BUT THAT HE FELT IT WAS SAFE AND LEGAL TO DISPATCH. AFTER CONFERRING WITH FO AGAIN AND BEING ASSURED BY MAINT AND THE DUTY MANAGER THAT WE WERE DEFERRING PROPERLY; WE AGREED TO TAKE THE AIRPLANE TO AVOID AT THE VERY LEAST AN EXTENDED DELAY AND MORE PROBABLY A CANCELLATION. ONCE ENRTE WE AGAIN DISCUSSED THE SITUATION AND I BEGAN TO SECOND GUESS OUR DECISION. I KNOW FROM MY WORK ON THE MEL RE-WRITE COMMITTEE THAT THE BOEING MASTER MEL PREAMBLE MAKES SOME REFERENCE TO A MEL CARD NEVER TAKING INTO CONSIDERATION ANOTHER INOPERATIVE COMPONENT IN ANOTHER MEL CARD. IN OTHER WORDS; CARD X (PACK INOP) FLT CREW OPS PLACARD SAYS THAT THE REMAINING PACK MUST OPERATE NORMALLY. I BELIEVE THAT THIS IS THE INTENT; THAT ALL COMPONENTS OF THE PACK (IE; PRESSURIZATION AND AIR CONDITIONING) OPERATE NORMALLY. FOR EXAMPLE; ASSUME THAT WE HAD NO DEFERRALS. ENRTE WE HAVE A PROBLEM WITH OUR L PACK AUTO TEMP CONTROLLER (WHICH WAS ONE OF OUR DEFERRALS Y). CONSULTING THE FLT MANUAL IRREGULAR PROCEDURE FOR THE OVER TEMP PROBLEM; WE ARE TOLD TO OPERATE THE CTLR IN STBY AND OUR PROBLEM IS SOLVED. WE ARE NOW OPERATING ON TWO PACKS; ONE IN AUTO AND ONE IN STBY. I BELIEVE THIS IS A 'FAIL-SAFE' OPERATION. THE KEY POINT HERE IS THAT WE STILL HAVE A BACK-UP PACK FOR PRESSURIZATION AND AIR CONDITIONING IF THE STBY CTLR SHOULD SUBSEQUENTLY FAIL. MY POINT HERE (AND I BELIEVE THIS SHOWS THE INTENT OF THE MEL) IS THAT WE WERE DEFERRED WITH THE R PACK INOP AND THE L PACK AUTO CTLR INOP. NOW IF THE L PACK STBY TEMPERATURE CTLR FAILS; WE HAVE NO PACKS AND ARE THEREFORE UNPRESSURIZED AND DOING A HIGH DIVE! I KNOWTHIS PROBABLY SOUNDS MORE COMPLICATED THAN IT NEEDS BE; BUT REMEMBER THAT WHILE WE HAVE TIME NOW TO WRITE AND ATTEMPT TO UNDERSTAND THIS RPT; IN REALITY WE WERE IN REAL TIME; ALREADY LATE; BEING CONSTANTLY BOMBARDED WITH FLT ATTENDANTS; PAX; GATE AGENTS; ZONE; PUSH CREW; AND MAINT WANTING TO KNOW WHAT WAS GOING ON AND WHEN WOULD WE BE READY TO PUSH! I MIGHT ALSO ADD THAT THIS IS ONLY MY 2ND DAY USING THE NEW MAINT DOC WITH APPROVED OPS PLACARD INFO IN LIEU OF THE FULL MEL CARD. IN BOTH OF THE MEL ITEMS REFERENCED ABOVE; THERE IS NO REFERENCE FOR THE FLT CREW OF WHERE THE DEFERRED STICKERS OR PLACARDS ARE TO BE PLACED. BECAUSE OF MY WORKING KNOWLEDGE WITH THE MEL RE-WRITE AT MAINT HQ A COUPLE OF YEARS AGO; I KNEW THAT ONE OF THE STICKERS IN THIS DEFERRAL WAS MISSING ENTIRELY AND THE OTHER WAS NOT PROPERLY PLACED ON THE PANEL. I HAD TO PULL DOWN BOTH MEL CARDS TO CONFIRM THIS INFORMATION. IF THE NEW FORMATTED MAINT DOC GIVES US ALL THE INFORMATION WE NEED; WILL THE PIC STILL BE HELD RESPONSIBLE FOR MISSING OR WRONGLY PLACED DECALS OR PLACARD INFORMATION DURING A FAA LINE CHECK? IF THE ANSWER IS YES; THEN WE NEED MORE OPS PLACARD INFORMATION OR WE SHOULD STILL BE PULLING DOWN ENTIRE MEL CARDS FOR EVERY DEFERRAL.SUPPLEMENTAL INFO FROM ACN 746689: UPON REVIEWING THE LOGBOOK DURING THE PREFLT; THE CAPT NOTICED A POSSIBLE PROBLEM CONCERNING TWO DEFERRED ITEMS THAT EXISTED CONCURRENTLY. THE DEFECTS AND CORRESPONDING DEFERRALS IN QUESTION ARE DESCRIBED BELOW: 1) 1 DEFECT: 'L PACK AUTO TEMP CONTROL SYSTEM(S) INOPERATIVE' (MEL REF Y) FLT CREW DIRECTIVE: A) ASSOCIATED PACK STANDBY TEMPERATURE CONTROL SYSTEM MUST OPERATE NORMALLY 2) 2 DEFECT: 'R AIR CONDITIONING PACK INOPERATIVE' (MEL REF# X). FLT CREW DIRECTIVE: A) REMAINING AIR CONDITIONING PACK MUST OPERATE NORMALLY B) MAINTAIN ASSOCIATED PACK SELECTOR IN 'OFF' POSITION FOR ALL PHASES OF FLT C) ADVISE PURSER SINCE WE WERE REQUIRED BY THE ABOVE MEL Y TO OPERATE THE L PACK IN THE STANDBY MODE; WE WERE CONCERNED THAT WE WOULD NOT SATISFY THE REQUIREMENTS OF MEL X WHICH REQUIRED THE OPERATING PACK TO OPERATE NORMALLY. WE DISCUSSED WHAT CONSTITUTED A PACK SYSTEM THAT 'MUST OPERATE NORMALLY.' WE ATTEMPTED TO GET CLARIFICATION FROM MAINT AND THE FODM BY SOLICITING THEIR INTERPRETATION OF WHAT CONSTITUTED NORMAL PACK OPERATION. THE MECHANIC STATED THAT 'THE LEFT PACK DOES OPERATE NORMALLY; SO WE ARE GOOD.' THE CAPT GOT A SIMILAR RESPONSE FROM THE FODM. WE WERE INITIALLY SATISFIED WITH THEIR ASSESSMENT AND CONSIDERED THE MAINT STATUS ACCEPTABLE AND WITHIN THE LIMITATIONS OF THE MEL AND DEPARTED. ONCE AIRBORNE; AND AFTER A THOROUGH DISCUSSION WITH THE CAPT; WE BOTH AGREED THAT PERHAPS THE L PACK SHOULD NOT BE CONSIDERED TO BE OPERATING NORMALLY WHEN REQUIRED BY MEL TO OPERATE IN STANDBY MODE. IN RETROSPECT; I NOW CONSIDER OUR FLT AS AN ILLEGAL DISPATCH DUE TO CONFLICTING REQUIREMENTS OF CONCURRENT MEL CARDS.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES: CURRENTLY THEIR SYSTEM OF MEL DEFERRALS DOES NOT RECOGNIZE WHEN TWO MELS ARE CONCURRENTLY IN CONFLICT. IN THIS SITUATION; R PACK IS INOP AND L PACK; WITH AUTO TEMP MODE CONTROL INOP AND ONLY THE STANDBY CONTROL IS FUNCTIONING. WITH R PACK ALREADY INOP AND IF THE L PACK STANDBY TEMP ALSO FAILS; THAN BOTH PACKS WOULD BE INOP AND CABIN WOULD BECOME UN-PRESSURIZED. THE ISSUE OF WHAT IS A NORMAL OPERATING SYSTEM NEEDS TO BE ADDRESSED. THE BOEING MASTER MEL (MMEL) PREAMBLE APPEARS TO MAKE SOME REFERENCE TO A MEL CARD NEVER TAKING INTO CONSIDERATION ANOTHER INOPERATIVE COMPONENT IN ANOTHER MEL CARD.

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.