A Line Mechanic reports having to pressurize a B757-200 to 6.0 PSI cabin differential pressure to locate a chronic air leak at cabin door 1-Left. Boeing Maintenance Manual procedures required Maintenance to coordinate with Boeing whenever cabin differential pressurization checks went above 4.50 PSI.

NASA callback

Reporter stated the B757 had numerous write-ups for an air leak at door 1-Left that multiple attempts to locate just where the leak was coming from had not been successful. He decided to continue pressurizing the aircraft; increasing the cabin differential pressure above 4.5 to 5.6 to 6.0 PSI differential. As soon as he reach just about 5.9 to 6.0 differential; door 1-Left started singing and whistling. More then one leak was discovered.Reporter stated the pressurization leaks were actually coming from the contour filler material around the door fuselage structure; not the door pressure seal. Repairing the filler would require removing; refilling and smoothing the filler material around the curved sections of the door fuselage structure.Reporter stated he realizes he wrote in the Logbook entry that he had pressurized the aircraft to approximately 6.50 PSI; but he actually never went above 6.0 differential pressure. By the time he reached 6.0; the cabin differential already started to fluctuate because the over-pressurization valves started to open. The aircraft was taken off the gate and move to the hangar to repair the filler material and perform Inspections that Boeing required after any pressurization of the fuselage above 4.5 PSI differential. Going above 4.5 PSI was not the issue with Boeing; they just wanted Maintenance to co-ordinate with Boeing and perform specific inspections of the cabin after the pressurization was completed.