Narrative:

I received a call from contract maintenance early saturday morning due to flight crew requesting engine oil service on #1 engine. I checked our computer system to make sure this was not an originating flight; and determined that this was a charter arriving early from ZZZ1. I authority/authorized the contract mechanic to service the engine oil and call back for a work order number. He called back shortly thereafter to ask what typically is added to the -700 aircraft engine oil during servicing; and he had stated that he had already added 3 quarts. He informed me that on the previous leg; maintenance had changed a component on the #1 engine for an oil leak. I asked the contract mechanic to service the engine oil to full and call back with the total amount of quarts he had added. While I was waiting for him to call back; I researched what had been done to the #1 engine. The research revealed that the #1 engine idg garlock seal had been replaced. When the mechanic called back; he reported that he had added 6 quarts of engine oil to #1 engine. I thought in my opinion that this amount was not abnormal. I also suggested the running of #1 engine if he or the crew felt uncomfortable due to recent work to the engine. I imagined that ZZZ1 did not top off the engine after the repairs were made. The logbook showed the servicing of #1 engine. Maintenance added 3 quarts of oil; but the oil entry section of the logbook had been lined through. There were no reported signs of an oil leak in or around the #1 engine as these phones calls were transacted. The aircraft departed for a return trip. 2 hours after the aircraft had departed; I received a call from a dispatcher stating that aircraft was having #1 engine oil quantity problems. I asked the dispatcher to ACARS the crew for quantity numbers. They reported departing with 93% oil quantity. 1 hour out; the percent was 74%; and at 2 hours out; the quantity was down to 57%. I checked the computer for flight information and determined that the flight had an additional 2+ hours of flight time. I made the decision; along with the dispatcher; to divert the aircraft because in my opinion the aircraft wouldn't have made it with 57% oil quantity remaining. The aircraft was near ZZZ2; where we had a mechanic on staff and the aircraft diverted. I called the mechanic to inform him of the diversion. I told him that we svced oil in ZZZ and mechanic in ZZZ1 had worked this engine 1 leg prior. After the aircraft had landed safely; I received a call from mechanic in ZZZ1 inquiring if aircraft was returning. I replied that the aircraft had diverted for #1 engine oil quantity problem. I told him that when we fixed the aircraft it would continue on to ZZZ1. Not long after this took place; my team lead informed me that he had spoke to a supervisor in ZZZ1 and that they believed that an o-ring was possibly missing from the newly installed garlock seal on #1 engine. I sent all necessary parts to ZZZ2 and informed the mechanic of my knowledge that maintenance had left an o-ring off during assembly of the garlock seal on #1 engine idg. We confirmed this after removal of the idg. Supplemental information from acn 660856: the mechanics notified their supervisor that they may have left an o-ring off of the outer case of the garlock seal. The supervisor call me at maintenance control and asked me to write a planning item to inspect the garlock for a missing o-ring. A planning item may be a few days before it is issued. My plan was to see of the engine was using oil in ZZZ and have the seal repaired. The aircraft did not arrival in ZZZ until my shift was over and I had planned to turn over the problem to the next controller on shift. When he arrived we had several events happen during the turnover time period and I failed to tell the next controller about the possible missing o-ring. As a result; the seal was not inspected and the engine lost oil on the return flight from ZZZ to ZZZ1 and was diverted to ZZZ2 where the seal was repaired.

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Original NASA ASRS Text

Title: A B737-700 DIVERTED DUE TO LOSS OF ENG OIL DUE TO IMPROPER DRIVE CASE SEAL INSTALLATION.

Narrative: I RECEIVED A CALL FROM CONTRACT MAINT EARLY SATURDAY MORNING DUE TO FLT CREW REQUESTING ENG OIL SVC ON #1 ENG. I CHKED OUR COMPUTER SYS TO MAKE SURE THIS WAS NOT AN ORIGINATING FLT; AND DETERMINED THAT THIS WAS A CHARTER ARRIVING EARLY FROM ZZZ1. I AUTH THE CONTRACT MECH TO SVC THE ENG OIL AND CALL BACK FOR A WORK ORDER NUMBER. HE CALLED BACK SHORTLY THEREAFTER TO ASK WHAT TYPICALLY IS ADDED TO THE -700 ACFT ENG OIL DURING SVCING; AND HE HAD STATED THAT HE HAD ALREADY ADDED 3 QUARTS. HE INFORMED ME THAT ON THE PREVIOUS LEG; MAINT HAD CHANGED A COMPONENT ON THE #1 ENG FOR AN OIL LEAK. I ASKED THE CONTRACT MECH TO SVC THE ENG OIL TO FULL AND CALL BACK WITH THE TOTAL AMOUNT OF QUARTS HE HAD ADDED. WHILE I WAS WAITING FOR HIM TO CALL BACK; I RESEARCHED WHAT HAD BEEN DONE TO THE #1 ENG. THE RESEARCH REVEALED THAT THE #1 ENG IDG GARLOCK SEAL HAD BEEN REPLACED. WHEN THE MECH CALLED BACK; HE RPTED THAT HE HAD ADDED 6 QUARTS OF ENG OIL TO #1 ENG. I THOUGHT IN MY OPINION THAT THIS AMOUNT WAS NOT ABNORMAL. I ALSO SUGGESTED THE RUNNING OF #1 ENG IF HE OR THE CREW FELT UNCOMFORTABLE DUE TO RECENT WORK TO THE ENG. I IMAGINED THAT ZZZ1 DID NOT TOP OFF THE ENG AFTER THE REPAIRS WERE MADE. THE LOGBOOK SHOWED THE SVCING OF #1 ENG. MAINT ADDED 3 QUARTS OF OIL; BUT THE OIL ENTRY SECTION OF THE LOGBOOK HAD BEEN LINED THROUGH. THERE WERE NO RPTED SIGNS OF AN OIL LEAK IN OR AROUND THE #1 ENG AS THESE PHONES CALLS WERE TRANSACTED. THE ACFT DEPARTED FOR A RETURN TRIP. 2 HRS AFTER THE ACFT HAD DEPARTED; I RECEIVED A CALL FROM A DISPATCHER STATING THAT ACFT WAS HAVING #1 ENG OIL QUANTITY PROBS. I ASKED THE DISPATCHER TO ACARS THE CREW FOR QUANTITY NUMBERS. THEY RPTED DEPARTING WITH 93% OIL QUANTITY. 1 HR OUT; THE PERCENT WAS 74%; AND AT 2 HRS OUT; THE QUANTITY WAS DOWN TO 57%. I CHKED THE COMPUTER FOR FLT INFO AND DETERMINED THAT THE FLT HAD AN ADDITIONAL 2+ HRS OF FLT TIME. I MADE THE DECISION; ALONG WITH THE DISPATCHER; TO DIVERT THE ACFT BECAUSE IN MY OPINION THE ACFT WOULDN'T HAVE MADE IT WITH 57% OIL QUANTITY REMAINING. THE ACFT WAS NEAR ZZZ2; WHERE WE HAD A MECH ON STAFF AND THE ACFT DIVERTED. I CALLED THE MECH TO INFORM HIM OF THE DIVERSION. I TOLD HIM THAT WE SVCED OIL IN ZZZ AND MECH IN ZZZ1 HAD WORKED THIS ENG 1 LEG PRIOR. AFTER THE ACFT HAD LANDED SAFELY; I RECEIVED A CALL FROM MECH IN ZZZ1 INQUIRING IF ACFT WAS RETURNING. I REPLIED THAT THE ACFT HAD DIVERTED FOR #1 ENG OIL QUANTITY PROB. I TOLD HIM THAT WHEN WE FIXED THE ACFT IT WOULD CONTINUE ON TO ZZZ1. NOT LONG AFTER THIS TOOK PLACE; MY TEAM LEAD INFORMED ME THAT HE HAD SPOKE TO A SUPVR IN ZZZ1 AND THAT THEY BELIEVED THAT AN O-RING WAS POSSIBLY MISSING FROM THE NEWLY INSTALLED GARLOCK SEAL ON #1 ENG. I SENT ALL NECESSARY PARTS TO ZZZ2 AND INFORMED THE MECH OF MY KNOWLEDGE THAT MAINT HAD LEFT AN O-RING OFF DURING ASSEMBLY OF THE GARLOCK SEAL ON #1 ENG IDG. WE CONFIRMED THIS AFTER REMOVAL OF THE IDG. SUPPLEMENTAL INFO FROM ACN 660856: THE MECHS NOTIFIED THEIR SUPVR THAT THEY MAY HAVE LEFT AN O-RING OFF OF THE OUTER CASE OF THE GARLOCK SEAL. THE SUPVR CALL ME AT MAINT CONTROL AND ASKED ME TO WRITE A PLANNING ITEM TO INSPECT THE GARLOCK FOR A MISSING O-RING. A PLANNING ITEM MAY BE A FEW DAYS BEFORE IT IS ISSUED. MY PLAN WAS TO SEE OF THE ENG WAS USING OIL IN ZZZ AND HAVE THE SEAL REPAIRED. THE ACFT DID NOT ARR IN ZZZ UNTIL MY SHIFT WAS OVER AND I HAD PLANNED TO TURN OVER THE PROB TO THE NEXT CONTROLLER ON SHIFT. WHEN HE ARRIVED WE HAD SEVERAL EVENTS HAPPEN DURING THE TURNOVER TIME PERIOD AND I FAILED TO TELL THE NEXT CONTROLLER ABOUT THE POSSIBLE MISSING O-RING. AS A RESULT; THE SEAL WAS NOT INSPECTED AND THE ENG LOST OIL ON THE RETURN FLT FROM ZZZ TO ZZZ1 AND WAS DIVERTED TO ZZZ2 WHERE THE SEAL WAS REPAIRED.

Data retrieved from NASA's ASRS site as of January 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.