B757-200
Maintenance Powerplant; Maintenance Airframe
Maintenance Technician 28
Troubleshooting; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors; Procedure; Manuals
A B757-200 aircraft arrived with a pilot report reading squeal at Left-2 (L-2) [cockpit] window with aircraft at 17;000 FT and a cabin differential pressure of 6.5 PSI. During the initial inspection; we found irregularities at the window jam which we found to be within limits. We burnished; primed; painted; and smoothed the [window] jam. During the confirmation pressurization [check]; we inadvertently over-pressurized by approximately 2 PSI. The aircraft; while in [another Maintenance Base]; went through a complete check as outlined by Boeing; with no damage found.
Reporter stated he was referring to the Captain's left sliding window (L-2). Initially they went to a 2.5 PSI cabin differential pressure check with no squeal noted. He did repair minor damages on the window frame jam caused by screws from the previous sliding window that had been replaced recently. But after re-reading the pilot's squawk; he decided they had to pressurize the aircraft to at least the same cabin pressure (6.5 PSI) when the squeal was noted by the flight crew. He followed the Aircraft Maintenance Manual (AMM) for the cabin pressure check. Again no squeals occurred. After he had signed-off the window discrepancy; the same squeal was written-up again on the next flight into ZZZ1.Reporter stated a 'red flag' went up at the downline Station when ZZZ1 mechanics had noted in the Maintenance History of the B757 aircraft; that a cabin High Pressure Differential Check had been performed without any reference to the Fault Isolation Manual (FIM) procedures for cockpit window squeal reports. The FIM check procedures have specific requirements and calculations that are suppose to be accomplished along with checking certain equipment; including Pitot Static pressure flex lines. He was not aware of any FIM procedures for window pressure squeals. ZZZ1 mechanics performed another cabin presssure check and found a fuselage HI-LOK fastener was leaking near the pressure seal for the sliding window.
A Line Mechanic reports how his lack of knowledge of a reference in the Fault Isolation Manual (FIM) for cockpit window pressure squeals; contributed to his not performing a proper cabin High Pressure Differential Pressure Check on a B757-200 aircraft. The Captain's left sliding window area had chronic pressure squeals.