As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ETOPS SIGNIFICANT SYS - LEFT DUCT PRESSURE FLUCTUATES WITH ENGINE RUNNING AND BLEED AIR SWITCH ON. OPERATES NORMALLY IN CRUISE. WHEN POWER COMES BACK DURING DESCENT, RT PRESSURE STICKS AND LT FLUCTUATES. PRONOUNCED AIR SURGE SOUND THRU ACFT PACKS. REPLACED PRV CONTROLLER IAW MM 36-11-19. REPLACED PRSOV IAW MM 36-11-09.