The school of hard shocks.
We were 58 days into a seven-month deployment onboard USS Theodore Roosevelt (CVN-71), and things were going smoothly. I was in the AME work center when we got a VIDSMAF for a popping liquid-cooling-system (LCS) fan circuit breaker. I checked the debrief in IETMS but found no troubleshooting recommendations. It was time for some old-school troubleshooting: schematics.
We checked out our tools, put the MAF in work, grabbed the schematics and PEDD, and went to the AE shop with a few questions. The AEs confirmed that a symbol in the schematics was a thermal switch; we suspected it had failed and caused the LCS cooling-fan motor to short out. We knew that, when external power was applied to the aircraft, we could turn on the fan with its test switch. We pulled the cannon plug from the fan, thereby eliminating it from the system, so we could determine if it was the source of the problem.
WE PUT ONE TECHNICIAN in the cockpit to apply power and another next to panel 10L to operate the LCS fan-test switch and watch circuit breakers. I was up on the aircraft in panel 205L to verify that the fan worked. After I removed the cannon plug from the LCS fan, we applied power and flipped the fan-test switch. No circuit breakers popped, so I decided to test the LCS cooling-air shutoff valve (SOV), which was the other possible cause of the popping breakers within the system. Trying to troubleshoot quickly and thoroughly before an upcoming maintenance meeting, I pulled the cannon plug off of the SOV, and it unexpectedly arced, burnt the cannon plug, and shut down the system. We cut power and disconnected the power cord.
I went to Maintenance Control and told them what I had done. I also said we now needed to change the LCS fan. After removing and replacing the bad SOV, LCS fan, and SOV cannon plug, the system op-checked 4.0.
This incident wouldn't have occurred if we had read the wires in the system we were testing and eliminated the suspect components one by one. We also should have made sure that power was secured before disconnecting any cannon plugs. Finally, we shouldn't have rushed.
The PEDD is a wonderful tool that displays notes, warnings and cautions not found in the schematics. Therefore, when troubleshooting outside the PEDD, note the pop-ups that would prevent injuries to personnel and damage to equipment. Also, brief your entire maintenance crew. Never be afraid to ask for help if you're not 100 percent sure how to complete a certain task.
"Safe and expeditious maintenance" is our squadron's motto. While striving for the expeditious, we bypassed the safe portion of our doctrine. In the end, this maintenance wasn't safe or expeditious.
By AME2 Josef Schmidt
Petty Officer Schmidt works in the AME shop at VFA-31.
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|Date:||Jun 22, 2009|
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