RECENTLY ACQUIRED B737-300 EXPERIENCES LOSS OF PRESSURIZATION. FO RPTS PRESSURE FROM COMPANY TO REVISE RPT OF INAPPROPRIATE FLT IN RVSM AIRSPACE.

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THE ACFT INVOLVED IN THIS INCIDENT WAS JUST ADDED TO THE COMPANY OPS SPECS. THE CREW WAS INFORMED THAT ALL APPROPRIATE PAPERWORK WAS IN ORDER AND THE ONLY LIMITING FACTOR WAS AN OUT-OF-DATE DATABASE FOR THE FMC. UPON PUSHBACK; AFTER THE AFTER START CHKLIST HAD BEEN COMPLETED; THERE WAS A NOTICEABLE SPLIT BTWN DUCT PRESSURES WHICH HAD BEEN NORMAL SINCE I HAD FLOWN THE ACFT FROM EUROPE WITH THE SAME PRESSURE SPLIT. TKOF AND CLB WERE NORMAL AND UPON REACHING CRUISE AT FL330; THE CABIN ALT WARNING HORN SOUNDED. WE COMPLETED PROCS PER THE QRH AND WERE UNABLE TO CTL THE CABIN PRESSURE; SO A DSCNT TO FL240 WAS INITIATED AND UPON REACHING FOUND WE WERE UNABLE TO MAINTAIN CABIN PRESSURE AND OPTED TO RETURN TO STL WHERE MAINT COULD ADDRESS THE PROB. THE FLT LANDED WITHOUT INCIDENT BUT THE REASON FOR THE RPT IS THAT COMPANY HAD FAILED TO RECEIVE TOTAL OPS SPECS APPROVAL ON ALL AMENDMENTS; MOST OF ALL THE APPROVAL FOR OP IN RVSM AIRSPACE. ADDITIONALLY; THE COMPANY IS TRYING TO SHIFT BLAME FROM THEMSELVES TO THE CREW BECAUSE I WAS ASKED TO CHANGE MY LINE RPT TO OMIT THE MENTION OF HARD ALTS.