B737-700
Maintenance Airframe; Maintenance Powerplant
Maintenance Inspector 3.5; Maintenance Lead Technician 17
Communication Breakdown; Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Diverted; General Maintenance Action
Chart Or Publication; Aircraft; Human Factors; Procedure
I gave an 'OK to Close' on a work card for panel number 194e on a B737-700 aircraft [while] following a contract customer's Air Carrier Maintenance Procedures Manual (MPM) procedures for that inspection. After the aircraft had been in service for several months; the flight crew experienced a pressurization issue and diverted the flight for investigation. During troubleshooting by the air carrier's mechanics; it was discovered that four drain valves under panel 194e were not installed. These valves were removed in April 2012; In Accordance With (IAW) Routine Check Card XXX. The installation of these valves were signed for by a Mechanic and a Quality Control (QC) Inspector (not myself); [approximately] five days later on the same card. The 'OK to Close' inspection requirements for this area is to look for FOD and obvious damage; I found neither at that time. The area of the inspection was on the aircraft exterior skin just aft of the main wheel well. The belly drains in question are common to the aft cargo bay. I was made aware that there was an issue months later.
Reporter stated the inflight pressurization issues that later developed on the B737-700 aircraft were due to the lack of lower fuselage drain valves that would normally close under cabin pressurization had they been reinstalled. Company Quality Assurance (Q/A) recognized they had to do something about the different Job Card procedure that contributed to the drain valves not being reinstalled.
A contract Repair Station Inspector reports about four lower fuselage drain valves that were not reinstalled on a customer Air Carrier's B737-700 aircraft. Flight crew had diverted due to a pressurization issue.