Narrative:

Maintenance employee sent a deferral on aircraft 'automatic pressurization system.' per the maintenance manual 21-30-00 troubleshooting the system tested normal. Fault code 30 showed low flow/high leak. He was unable to perform a pressure health check due to not enough personnel. Without looking at the maintenance manual; troubleshooting reference and the fault code given along with the 3 questions on the deferral: 1) the original discrepancy of the MEL 'did not' change; 2) the aircraft 'was' still configured per the MEL dispatch deviation procedures; 3) troubleshooting 'was' performed; I felt the MEL was correct and just needed further troubleshooting. I will request and confirm any maintenance manual troubleshooting and fault codes given on any deferrals. Supplemental information from acn 817068: inbound (flight) report: automatic pressurization failed at FL360 regained control of cabin in alternate mode at FL210. I placarded automatic mode inoperative. Reference was the MEL 21. Callback conversation with reporter acn 817069 revealed the following information: reporter stated the manual AC; manual dc and standby position pressurization controls worked fine on the B737-500. But in the auto mode position; the 'auto fail' light illuminating was a chronic problem. The aircraft was grounded at a downline station; where the pressurization health check was accomplished. Reporter stated he was told a plastic tie wrap was found restricting the main (aft) outflow valve. Reporter stated that didn't make any sense; because the pressurization system worked fine in the manual and standby modes and was originally deferred because they were working fine; except for the position. Reporter stated the main (aft) outflow valve was replaced and dirt was found in the aft cargo drain valve.

Related reports:

Google
 

Original NASA ASRS Text

Title: A Maintenance Controller describes why he continued an MEL deferral of a B737-500 with a chronic cabin 'auto pressurization system' problem.

Narrative: Maintenance employee sent a deferral on aircraft 'automatic pressurization system.' Per the maintenance manual 21-30-00 troubleshooting the system tested normal. Fault code 30 showed low flow/high leak. He was unable to perform a pressure health check due to not enough personnel. Without looking at the maintenance manual; troubleshooting reference and the fault code given along with the 3 questions on the deferral: 1) the original discrepancy of the MEL 'DID NOT' change; 2) the aircraft 'WAS' still configured per the MEL Dispatch Deviation Procedures; 3) Troubleshooting 'WAS' performed; I felt the MEL was correct and just needed further troubleshooting. I will request and confirm any maintenance manual troubleshooting and fault codes given on any deferrals. Supplemental information from ACN 817068: Inbound (flight) report: automatic pressurization failed at FL360 regained control of cabin in alternate mode at FL210. I placarded automatic mode inoperative. Reference was the MEL 21. Callback conversation with reporter ACN 817069 revealed the following information: Reporter stated the Manual AC; Manual DC and Standby position pressurization controls worked fine on the B737-500. But in the auto mode position; the 'auto fail' light illuminating was a chronic problem. The aircraft was grounded at a downline station; where the Pressurization Health Check was accomplished. Reporter stated he was told a plastic tie wrap was found restricting the main (aft) outflow valve. Reporter stated that didn't make any sense; because the pressurization system worked fine in the manual and standby modes and was originally deferred because they were working fine; except for the position. Reporter stated the main (aft) outflow valve was replaced and dirt was found in the aft cargo drain valve.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.