Narrative:

During preflight; a check of the logbook revealed a placard 'right pack inoperative in automatic; use manual.' the MEL relief that was cited actually deferred the automatic temperature control system; not the pack. The right pressure indicator showed about 10 psi static with the pack selected on; but the pack was; in fact; inoperative. There was no airflow with the right pack selected on; and no increase in pack pressure. Maintenance was summoned. They checked and confirmed the right pack was inoperative. A new placard was issued; along with a new flight plan; and more fuel; for pack inoperative dispatch limited to FL250. A further review of the logbook was instructive; and discomforting. 7 days earlier; a discrepancy was entered 'right air conditioning shows no flow.' the signoff maintenance entry was scribbled; with a line-out; and very hard to read; but appeared to say 'recycled fan switch (recirculation) air condition operations check normal ok for service.' it is hard to determine what the corrective action was; but apparently -- no action taken by maintenance. On the next day the cabin (right) temperature control system was squawked -- 'temperature control valve goes to full hot in automatic; ok in manual.' maintenance replaced the temperature controller and signed it off. However; the temperature control write-up was repeated almost every day after that -- 5 times total -- resulting in some cases of a deferral of the automatic temperature control system; and in others; replacement of more components. Finally we come to the subject flight of this report; and there is nothing wrong with the temperature control; the pack is clearly inoperative. It is quite obvious that this airplane was flown for the past 7 days with an inoperative pack; without compliance with the MEL or the operating limitation of FL250. This happened because of the poor design characteristics of the MD80 air supply system; mis-diagnosis by flight crews; and a lack of adequate maintenance troubleshooting and corrective action. As a result our passenger were exposed to the real possibility of a high-altitude depressurization; not to mention the discomfort associated with single-pack operations in the summertime. The problem was probably disguised by several factors. The erroneous pack pressure gauge indicated some pressure; albeit not in the normal range. The pack pressure gauge 'bounced' when the switch was selected (pack pressure gauges are notoriously unreliable). And the recirculation fan may have been on when tactile flow checks were carried out; which might lead one to erroneously conclude a pack is operating when it is not. And finally there was a 'red herring' -- the uncontrollable movement of the cabin temperature control valve towards full hot at cruise altitude; which can happen as a result of a lack of airflow. So the repeated automatic temperature control problems were actually the result of an undetected inoperative pack. (In manual the valve position can be successfully controled; even if there is no airflow from the pack.) I suspect a pressure regulator valve malfunction. The flight crew training; maintenance troubleshooting; and maintenance control procedures failed completely here; resulting in an undetected equipment failure and unsafe operation for 7 days.

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Original NASA ASRS Text

Title: AN MD80 ACFT FLEW FOR SEVEN DAYS WITH A MIS-DIAGNOSED RIGHT PACK AUTO TEMP PROBLEM WHEN IN FACT R PACK WAS ACTUALLY INOP AND FLYING AT NORMAL CRUISE ALTITUDE.

Narrative: DURING PREFLT; A CHK OF THE LOGBOOK REVEALED A PLACARD 'R PACK INOP IN AUTO; USE MANUAL.' THE MEL RELIEF THAT WAS CITED ACTUALLY DEFERRED THE AUTO TEMP CTL SYS; NOT THE PACK. THE R PRESSURE INDICATOR SHOWED ABOUT 10 PSI STATIC WITH THE PACK SELECTED ON; BUT THE PACK WAS; IN FACT; INOP. THERE WAS NO AIRFLOW WITH THE R PACK SELECTED ON; AND NO INCREASE IN PACK PRESSURE. MAINT WAS SUMMONED. THEY CHKED AND CONFIRMED THE R PACK WAS INOP. A NEW PLACARD WAS ISSUED; ALONG WITH A NEW FLT PLAN; AND MORE FUEL; FOR PACK INOP DISPATCH LIMITED TO FL250. A FURTHER REVIEW OF THE LOGBOOK WAS INSTRUCTIVE; AND DISCOMFORTING. 7 DAYS EARLIER; A DISCREPANCY WAS ENTERED 'R AIR CONDITIONING SHOWS NO FLOW.' THE SIGNOFF MAINT ENTRY WAS SCRIBBLED; WITH A LINE-OUT; AND VERY HARD TO READ; BUT APPEARED TO SAY 'RECYCLED FAN SWITCH (RECIRCULATION) AIR CONDITION OPS CHK NORMAL OK FOR SVC.' IT IS HARD TO DETERMINE WHAT THE CORRECTIVE ACTION WAS; BUT APPARENTLY -- NO ACTION TAKEN BY MAINT. ON THE NEXT DAY THE CABIN (R) TEMP CTL SYS WAS SQUAWKED -- 'TEMP CTL VALVE GOES TO FULL HOT IN AUTO; OK IN MANUAL.' MAINT REPLACED THE TEMP CTLR AND SIGNED IT OFF. HOWEVER; THE TEMP CTL WRITE-UP WAS REPEATED ALMOST EVERY DAY AFTER THAT -- 5 TIMES TOTAL -- RESULTING IN SOME CASES OF A DEFERRAL OF THE AUTO TEMP CTL SYS; AND IN OTHERS; REPLACEMENT OF MORE COMPONENTS. FINALLY WE COME TO THE SUBJECT FLT OF THIS RPT; AND THERE IS NOTHING WRONG WITH THE TEMP CTL; THE PACK IS CLRLY INOP. IT IS QUITE OBVIOUS THAT THIS AIRPLANE WAS FLOWN FOR THE PAST 7 DAYS WITH AN INOP PACK; WITHOUT COMPLIANCE WITH THE MEL OR THE OPERATING LIMITATION OF FL250. THIS HAPPENED BECAUSE OF THE POOR DESIGN CHARACTERISTICS OF THE MD80 AIR SUPPLY SYS; MIS-DIAGNOSIS BY FLT CREWS; AND A LACK OF ADEQUATE MAINT TROUBLESHOOTING AND CORRECTIVE ACTION. AS A RESULT OUR PAX WERE EXPOSED TO THE REAL POSSIBILITY OF A HIGH-ALT DEPRESSURIZATION; NOT TO MENTION THE DISCOMFORT ASSOCIATED WITH SINGLE-PACK OPS IN THE SUMMERTIME. THE PROB WAS PROBABLY DISGUISED BY SEVERAL FACTORS. THE ERRONEOUS PACK PRESSURE GAUGE INDICATED SOME PRESSURE; ALBEIT NOT IN THE NORMAL RANGE. THE PACK PRESSURE GAUGE 'BOUNCED' WHEN THE SWITCH WAS SELECTED (PACK PRESSURE GAUGES ARE NOTORIOUSLY UNRELIABLE). AND THE RECIRCULATION FAN MAY HAVE BEEN ON WHEN TACTILE FLOW CHKS WERE CARRIED OUT; WHICH MIGHT LEAD ONE TO ERRONEOUSLY CONCLUDE A PACK IS OPERATING WHEN IT IS NOT. AND FINALLY THERE WAS A 'RED HERRING' -- THE UNCONTROLLABLE MOVEMENT OF THE CABIN TEMP CTL VALVE TOWARDS FULL HOT AT CRUISE ALT; WHICH CAN HAPPEN AS A RESULT OF A LACK OF AIRFLOW. SO THE REPEATED AUTO TEMP CTL PROBS WERE ACTUALLY THE RESULT OF AN UNDETECTED INOP PACK. (IN MANUAL THE VALVE POS CAN BE SUCCESSFULLY CTLED; EVEN IF THERE IS NO AIRFLOW FROM THE PACK.) I SUSPECT A PRESSURE REGULATOR VALVE MALFUNCTION. THE FLT CREW TRAINING; MAINT TROUBLESHOOTING; AND MAINT CTL PROCS FAILED COMPLETELY HERE; RESULTING IN AN UNDETECTED EQUIP FAILURE AND UNSAFE OP FOR 7 DAYS.

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.