As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE LEFT ENGINE BLEED AIR CONTROL SYSTEM IS BEGINNING TO DETERIORATE. DURING CLIMB AND CRUISE THE LEFT ENGINE DUCT PRESSURE IS LOW FOR THE GIVEN POWER SETTINGS. ACCOMPLISHED TC NG36WC 00001 ENG BLEED AIR SYSTEM HEALTH CHECK. FOUND NR 1 ENG HIGH STAGE REGULATOR BAD. REMOVED AND REPLACED NR 1 ENG HIGH STAGE REGULATOR OPS CHECKS AND LEAK CHECKS GOOD REF MM 36 11 07. GROUND VERIFICATION SUCCESSFUL.