Narrative:

The right pack was deferred inoperative. That was all that was mentioned pertaining to flight plan items in my discussion with dispatch on the way to the airport. In looking deeper into the maintenance logbook on my preflight I also found the cabin press controller in auto 2 had been written up stating that the rate on the pressurization indicator panel was fluctuating up and down. Dispatch never mentioned that; and the word deferred; or inoperative; was never used. Also there was no orange sticker by the pressurization indicator panel like there was for the right pack being deferred inoperative. However; it did say operate in auto 1 which we did. Normal takeoff; departure; climb and cruise ensued. Everything operated normally. About the mid point of the flight at cruise altitude FL340 when the right pack off light--which was on as it should be with the pack switch in the off position and/or no airflow sensed--went out. We both looked at the right pack switch and it was still in the off position; the other pack was working properly; the duct pressure needles were still matched and normal. Even though the right pack switch was off the fact that the pack off lite was now out made us think that somehow airflow was being sensed to the right pack like a valve not fully closed. Since everything appeared normal we were going to include that information with a new write-up after landing. A short time later we got the cabin alt warning (lights and horn) the first officer was very quick to don his oxygen mask and select the switches for communication and get cabin alt/rapid decompression qrc out. As I was getting my oxygen mask out I was thinking this is weird because I didn't feel any popping in my ears at all and looked up at the pressurization indicator panel and the rate was neutral (not up or down) the cabin alt. Was in deed at 10;000 ft and not moving (i.e. Not going higher). And the pressure differential gauge looked normal with the needle pointing toward the left 7 to 8 psi. As I processed this information I finished with my adjustments with my mask and flight interphone switches and nodded that I was with the first officer and to confirm we were both ready to continue with the rest of the qrc. As I followed the first officer read the rest of the qrc I looked at the pressurization indicator panel and the cabin alt was still right at 10;000 ft. It seemed to be functioning normally except for holding 10;000 ft. In my mind I was thinking why not go down now we're just over 100 NM from ZZZ anyway. I stated to the first officer that I'm going to ask for lower altitude. I don't know if he heard me or not and that is probably the main lesson here. The communication was tough. I don't think we turned our speakers up; then both interphone selector and switch volume up. I called ATC and asked for a lower altitude. ATC responded by saying turn left 20 degrees and cleared down to 10;000 ft. In my mind it was a precautionary descent in case something turns south with the pressurization system and it doesn't hold 10;000 ft or in other words becomes truly uncontrollable. I don't think I communicated that to the first officer as clearly as I could have. The communication was tough. Left should have followed each step that the first officer was reading from the qrc more aggressively because the last step states if cabin altitude is uncontrollable---emergency descent accomplish. The cabin alt wasn't uncontrollable it was controllable I was descending normally as a proactive precaution. I think the first officer interpreted this as cabin altitude uncontrollable--emergency descent qrc accomplish. He proceeded to seek approval for reading the emergency descent qrc which wasn't necessary but I thought his intent was to be proactive and to read it as a review in case the pressure controller went south. We had control because it was holding a pressure differential; a cabin altitude although not the normal one; and the rate was neutral. We weren't in an emergency situation at the moment; we didn't declare an emergency because there was no reason to at that moment. ATC probably cleared us so readily because it was about the point to do so anyway. There were a lot of potential avenues for an emergency to develop but they just didn't. The descent was a normal with throttles at idle; normal airspeed; etc. I chose to allow the first officer to go ahead with the emergency descent qrc thinking he was being proactive and his intent was to read it as a review in case things went south. I could have done a better job of making sure that we were on that same sheet of music. When we got to 10;000 ft we had 90 NM to go to ZZZ. About that time ATC asked if we needed any assistance. We stated no. Prior to leveling at 10;000 ft the first officer communicated with the flight attendants that we had a pressure problem. Everything is under control just letting you know. That was the first hint that anything was abnormal as far as the flight attendants were aware of. They hadn't noticed anything out of the norm. The flight attendants later on mentioned that it was hard for them to understand the first officer while on the mask. We landed uneventfully; and after the parking checklist were discussing exactly how to write things up. In summary: #1 the right pack off light went out acting as if it were on and receiving air. #2 cabin altitude warning came on because the cabin alt indicator had hit 10;000 ft with other indications normal. #3 recapping the events and looking at the overhead panel in detail to help us with our write up we noticed the mode selector on the pressurization control panel was in auto 2 when it was suppose to be in auto 1 like it was on the first flight. We both didn't know how it got there but in going over the procedures we accomplished we agreed the highest likely hood was on my cockpit set up back at the departure station where I would put in the destination altitude per the manual it would be a very easy to forget the auto 2 had a gripe on it and we were to operate in auto 1 especially with no deferral sticker on it. It would be a good idea for maintenance to take a look at this and if there was any possibility of an operationally related effect from an abnormally functioning piece of equipment there ought to be an MEL; deferral # and a placard. I think we as a crew did a good job with this situation. But it could have been better. Contributing factors: #1 a better more detailed write up of the auto 2 rate gripe. Should there have been a sticker; a deferral number; etc. #2 communication during the cabin alt/rapid depressurization qrc; and then the confirmation by both us as to whether the cabin altitude was truly uncontrollable or not before continuing and the appropriate checklist to proceed with if any.

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Original NASA ASRS Text

Title: Dispatched with a pressurization system anomaly incompletely addressed by maintenance; the flight crew of a B757-200 encountered numerous problems reacting to a cabin altitude warning.

Narrative: The right pack was deferred inoperative. That was all that was mentioned pertaining to flight plan items in my discussion with Dispatch on the way to the airport. In looking deeper into the maintenance logbook on my preflight I also found the cabin press Controller in auto 2 had been written up stating that the rate on the pressurization indicator panel was fluctuating up and down. Dispatch never mentioned that; and the word deferred; or inoperative; was never used. Also there was no orange sticker by the pressurization indicator panel like there was for the right pack being deferred inoperative. However; it did say operate in Auto 1 which we did. Normal takeoff; departure; climb and cruise ensued. Everything operated normally. About the mid point of the flight at cruise altitude FL340 when the Right PACK off light--which was on as it should be with the pack switch in the off position and/or no airflow sensed--went out. We both looked at the right pack switch and it was still in the off position; the other pack was working properly; the duct pressure needles were still matched and normal. Even though the right pack switch was off the fact that the pack off lite was now out made us think that somehow airflow was being sensed to the right pack like a valve not fully closed. Since everything appeared normal we were going to include that information with a new write-up after landing. A short time later we got the Cabin Alt warning (lights and horn) the First Officer was very quick to don his oxygen mask and select the switches for communication and get Cabin Alt/Rapid decompression QRC out. As I was getting my oxygen mask out I was thinking this is weird because I didn't feel any popping in my ears at all and looked up at the pressurization indicator panel and the rate was neutral (not up or down) the cabin alt. was in deed at 10;000 FT and not moving (i.e. not going higher). And the pressure differential gauge looked normal with the needle pointing toward the left 7 to 8 PSI. As I processed this information I finished with my adjustments with my mask and flight interphone switches and nodded that I was with the First Officer and to confirm we were both ready to continue with the rest of the QRC. As I followed the First Officer read the rest of the QRC I looked at the pressurization indicator panel and the cabin alt was still right at 10;000 FT. It seemed to be functioning normally except for holding 10;000 FT. In my mind I was thinking why not go down now we're just over 100 NM from ZZZ anyway. I stated to the First Officer that I'm going to ask for lower altitude. I don't know if he heard me or not and that is probably the main lesson here. The communication was tough. I don't think we turned our speakers up; then both interphone selector and switch volume up. I called ATC and asked for a lower altitude. ATC responded by saying turn left 20 degrees and cleared down to 10;000 FT. In my mind it was a precautionary descent in case something turns south with the pressurization system and it doesn't hold 10;000 FT or in other words becomes truly uncontrollable. I don't think I communicated that to the First Officer as clearly as I could have. The communication was tough. l should have followed each step that the First Officer was reading from the QRC more aggressively because the last step states IF CABIN ALTITUDE IS UNCONTROLLABLE---Emergency Descent Accomplish. The cabin alt wasn't uncontrollable it was controllable I was descending normally as a proactive precaution. I think the First Officer interpreted this as cabin altitude uncontrollable--emergency descent QRC accomplish. He proceeded to seek approval for reading the emergency descent QRC which wasn't necessary but I thought his intent was to be proactive and to read it as a review in case the pressure controller went south. We had control because it was holding a pressure differential; a cabin altitude although not the normal one; and the rate was neutral. We weren't in an emergency situation at the moment; we didn't declare an emergency because there was no reason to at that moment. ATC probably cleared us so readily because it was about the point to do so anyway. There were a lot of potential avenues for an emergency to develop but they just didn't. The descent was a normal with throttles at idle; normal airspeed; etc. I chose to allow the First Officer to go ahead with the emergency descent QRC thinking he was being proactive and his intent was to read it as a review in case things went south. I could have done a better job of making sure that we were on that same sheet of music. When we got to 10;000 FT we had 90 NM to go to ZZZ. About that time ATC asked if we needed any assistance. We stated no. Prior to leveling at 10;000 FT the First Officer communicated with the flight attendants that we had a pressure problem. Everything is under control just letting you know. That was the first hint that anything was abnormal as far as the flight attendants were aware of. They hadn't noticed anything out of the norm. The flight attendants later on mentioned that it was hard for them to understand the First Officer while on the mask. We landed uneventfully; and after the parking checklist were discussing exactly how to write things up. In summary: #1 the right pack off light went out acting as if it were on and receiving air. #2 Cabin altitude warning came on because the cabin alt indicator had hit 10;000 FT with other indications normal. #3 Recapping the events and looking at the overhead panel in detail to help us with our write up we noticed the mode selector on the pressurization control panel was in auto 2 when it was suppose to be in auto 1 like it was on the first flight. We both didn't know how it got there but in going over the procedures we accomplished we agreed the highest likely hood was on my cockpit set up back at the departure station where I would put in the destination altitude per the manual it would be a very easy to forget the auto 2 had a gripe on it and we were to operate in auto 1 especially with no deferral sticker on it. It would be a good idea for maintenance to take a look at this and if there was any possibility of an operationally related effect from an abnormally functioning piece of equipment there ought to be an MEL; deferral # and a placard. I think we as a crew did a good job with this situation. But it could have been better. Contributing factors: #1 A better more detailed write up of the auto 2 rate gripe. Should there have been a sticker; a deferral number; etc. #2 communication during the Cabin Alt/Rapid Depressurization QRC; and then the confirmation by both us as to whether the cabin altitude was truly uncontrollable or not before continuing and the appropriate checklist to proceed with if any.

Data retrieved from NASA's ASRS site as of April 2012 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.