As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
L PACK PRESS DECREASES AS ALTITUDE INCREASES. AT 10K L40/R45 15K L37/R45 AT 20K L33/R45 25K L30/R45 30K L25/R45 35KL21/R45 37KL19/R45 CRUISE FL380 L21/45. FOUND BOTH THE PRECOOLER CONT VALVE & THE HIGH STAGE REGULATOR ON THE NR 1 ENG FAILED TO REGULATE THE PROPER PRESSURES. REPLACED THE NR 1 PCV REF AMM 36 12 02. REPLACED THE NR 1 HIGH STAGE REGULATOR REF AMM 36 11 07. OPS & LEAK CHECKS NORMAL. ENG BLEED AIR OPS TEST NML REF 36 11 00 710 801.