TWO MECHANICS REPORT THEY BELIEVE THE CABIN PRESSURIZATION LOSS AT 20000 FT OF ONE OF THEIR B757-200 ACFT IS A DIRECT RESULT OF CARRIER NOT PERFORMING UPGRADES TO THEIR PRESSURE CONTROLLERS AND ACTUATORS PER OLD SVC BULLETINS.

Narrative

ACFT LEFT ZZZ AND AT ABOUT 20000 FT LOST CABIN PRESSURIZATION. IT IS MY BELIEF THIS IS A DIRECT RESULT OF NOT PERFORMING SVC BULLETIN TO THE OLD CABIN PRESSURE CONTROLLER. AIRLINE STILL HAS A MIX OF OLD AND NEW CABIN PRESSURE CONTROLLERS. IF THE OLD UNITS WERE MODIFIED TO NEW UNITS AND ALL PRESSURE ACTUATOR UNITS WERE MODIFIED TO THE NEW CONFIGURATION THESE PRESSURIZATION PROBLEMS WOULD DROP DRAMATICALLY. PROBLEM HAS NOT BEEN FIXED.SUPPLEMENTAL INFO FROM ACN 804079: AIRLINE IS CURRENTLY FLYING WITH WHO KNOWS WHAT CONTROLLERS MIXED; BOTH OLD ACTUATORS AND NEW ACTUATORS MIXED TOGETHER ALONG WITH MODIFIED ACTUATORS (PRESSURE CONTROLLER ACTUATORS) AND UNMODIFIED ACTUATORS (PRESSURE CONTROLLER ACTUATORS -9; -10; -11). I FEEL THE CONTROLLERS SHOULD BE MODIFIED TO NEW ACTUATORS' LEVELS TO CORRECT THIS FROM HAPPENING.CALLBACK CONVERSATION WITH RPTR 804078 REVEALED THE FOLLOWING INFO: REPORTER STATED THAT FOR TEN YEARS THE B757 AND B767-300 CABIN PRESSURE CONTROLLERS (BLACK BOXES) ON ETOPS ACFT HAVE NOT BEEN UPGRADED DUE TO PARTS NOT BEING ORDERED. HIS CARRIER HAS RECENTLY BROUGHT THE MODIFICATION WORK OF THE CONTROLLER ACTUATORS BACK IN-HOUSE TO ACCOMPLISH MFG SVC BULLETIN. HOWEVER; PART OF THE ACTUATOR SVC BULLETIN REQUIRES THAT THE PRESSURE CONTROLLER UNIT MODIFICATION 'MUST BE DONE CONCURRENTLY' UNDER ANOTHER SVC BULLETIN. THIS HAS NOT BEEN DONE. THESE UN-MODIFIED CABIN PRESSURE CONTROLLERS ARE STILL BEING INSTALLED WITH THE UPGRADED PRESSURE CONTROLLER ACTUATORS. THIS PRACTICE IS CONTRARY TO HONEYWELL'S RECOMMENDATIONS. REPORTER STATED THIS COMBINATION OF UPGRADED CONTROLLER ACTUATOR WITH A NON-MODIFIED PRESSURE CONTROLLER UNIT CONTINUES TO CAUSE NUMEROUS AND ONGOING PILOT WRITE-UPS ABOUT ACFT OVER-PRESSURE CONTROL PROBLEMS IN FLIGHT AND ON THE GROUND AT THE GATES; ESPECIALLY DURING PUSHBACKS. THE MODIFIED ACTUATOR OVER-DRIVES THE OUTFLOW VALVE DOOR(S) AND JAMS THEM SHUT. THIS REQUIRES THE PILOT TO GO TO MANUAL CONTROL MODE OF OPERATION TO OVERRIDE THE OUTFLOW VALVE DOOR. HONEYWELL IS NOW THE LICENSEE OF THE ORIGINAL LEAR PRESSURE CONTROLLER EQUIPMENT. REPORTER ALSO STATED THAT HIS ENGINEERING GROUP DOES NOT BELIEVE THERE ARE ANY PROBLEMS AND HAS CHANGED THE WORDING OF THE ORIGINAL SVC BULLETIN MODIFICATION IMPLEMENTATION FROM 'ACCOMPLISH AT NEXT SHOP VISIT;' TO READ AS 'SVC BULLETIN IS FOR INFO ONLY.' THE HONEYWELL REP HE HAS TALKED WITH STRONGLY DISAGREES WITH ENGINEERING'S POSITION ON THIS ISSUE. HONEYWELL WILL ONLY DO A -15 PRESSURE CONTROLLER UPGRADE AS RECOMMENDED BY BOEING.