As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR RETURN DUE TO DUCT PRESSURE FLUCTUATING RAPIDLY 0-70 PSI ON CLIMBOUT BOTH ENGINES. AT LEVEL OFF PRESSURE BECAME INTERMITTENT. ON APPROACH PRESSURE DROPPED RUNNING AT HIGH POWER SETTING.REMOVED AND REPLACED RT ENG PRSOV PER FIM 36-10-00 AND AMM 36-11-18. OPS CHECK OK PER AMM 71-00-00 AND 36-11-00. ALSO REMOVED AIR SUPP MODULE P/N ON/OFF: 804401-2-005 S/N ON: 096050059 S/N OFF: 11090425.