A Line Mechanic loosely installed mount bolts during replacement of a Center Tank Fuel Quantity Transient Suppression Device (TSD) on a B737-300 aircraft to allow another Mechanic to connect a wire harness to the TSD. Mechanic realized after the aircraft departed that the mount bolts may not have been tightened.
Synopsis
A Line Mechanic loosely installed mount bolts during replacement of a Center Tank Fuel Quantity Transient Suppression Device (TSD) on a B737-300 aircraft to allow another Mechanic to connect a wire harness to the TSD. Mechanic realized after the aircraft departed that the mount bolts may not have been tightened.
Narrative
[I was] assigned [Job] Cards to change the # 1; 2 and Center Fuel Quantity Transient Suppression Device (TSD) boxes on a B737-300 aircraft and a Task Card to inspect the TSD harnesses. An inspection found the Center tank TSD harness bad. After writing a Non-Routine [Write-up] for the harness; I started on the TSD boxes on # 1; 2; and Center. I asked for another Aviation Maintenance Technician (AMT) to do the Remove and Replace (R/R) of the Center TSD harness. I then temporarily installed the Center TSD box with mount bolts finger tight to make it easier to connect the harness to the box. I did not convey this to the AMT doing the harness and he did not notice the loose bolts. I did look over the center TSD harness installation when he was finished; but did not notice the condition of the bolts. After going through the job mentally later that day; it occurred to me that the bolts may have been overlooked. The AMT installing the harness said he only did the harness connection to the box. It was at this time that I contacted Maintenance Control. The aircraft was Routine Overnight (RON) in ZZZ and the AMT there investigated; verified and corrected the loose bolts. There was a lack of communication between the two AMTs. I should be more thorough in my post maintenance inspection of work performed; and should not temporarily install parts.
NASA callback
Reporter stated they were changing out the Transient Suppression Devices (TSDs) per Engineering due to reliability issues involving fuel quantity indication fluctuations and irregular readings. Either Engineering; pilots; or both had noticed the Fuel Quantity Indication System seemed to be affected at various times when pilots were using flashing landing lights. It seems that a pulse effect was acting on the Fuel Indication System.Reporter stated the Center Fuel Tank TSD box is a sealed unit and mounted about centerline on the ceiling of the Main Landing Gear (MLG) wheelwell. The Center tank TSD harness that was replaced has Quick Disconnects (Q/Ds) at both ends and runs aft; from the MLG wheelwell forward bulkhead to the TSD box at the ceiling above the 'A' System Hydraulic Reservoir.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.