Narrative:

I was assigned to perform maintenance task; the in-flight shutdown inspection (ifsd) on air carrier X. Other technicians were assigned to replace the idg and the idg gearbox carbon seal. Upon completion of my assigned task; I assisted in the installation of the idg gearbox carbon seal. I removed the carbon seal for replacement. While cleaning and preparing the gearbox carbon seal cavity for seal installation; a new carbon seal was handed to me. I installed the carbon seal into the cavity without further inspection. I should have inspected carbon seal for proper confign by referring to the amm and the ipc and check for an o-ring. Idg installation was completed and svced per amm. Performed several engine run-ups per amm; idg disconnect check and no oil leak noted. All idg and engine indications were normal. Aircraft X took flight on same day. Aircraft returned to ZZZ due to low oil quantity and pressure indication. During troubleshooting; it was observed that the o-ring on the left engine idg carbon seal was missing. This was idented as the source of the oil leak on the engine. A new left idg carbon seal was installed per amm and ipc to correct the problem. I was notified by the aircraft maintenance department manager of the findings when I returned to work. Callback conversation with reporter revealed the following information: this engine was already being worked as a result of idg problems. Decision was made to perform an in-flight shutdown procedure on the engine to check for any physical discrepancies in the electrical wire bundles and associated hardware and connectors. Maintenance also decided to replace the idg. Part of the replacement of the idg requires a new carbon seal. Reporter also states when he was given the new carbon seal; he didn't notice the o-ring feature was not part of the carbon seal. They performed two engine runs and opened up the engine cowls to check for oil leaks; none were found. The aircraft departed and returned approximately five hours later with low oil.

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Original NASA ASRS Text

Title: A B767-300ER ACFT RETURNED TO FIELD DUE TO LEFT ENGINE OIL LOSS AFTER CARBON SEAL REPLACEMENT.

Narrative: I WAS ASSIGNED TO PERFORM MAINT TASK; THE INFLT SHUTDOWN INSPECTION (IFSD) ON ACR X. OTHER TECHNICIANS WERE ASSIGNED TO REPLACE THE IDG AND THE IDG GEARBOX CARBON SEAL. UPON COMPLETION OF MY ASSIGNED TASK; I ASSISTED IN THE INSTALLATION OF THE IDG GEARBOX CARBON SEAL. I REMOVED THE CARBON SEAL FOR REPLACEMENT. WHILE CLEANING AND PREPARING THE GEARBOX CARBON SEAL CAVITY FOR SEAL INSTALLATION; A NEW CARBON SEAL WAS HANDED TO ME. I INSTALLED THE CARBON SEAL INTO THE CAVITY WITHOUT FURTHER INSPECTION. I SHOULD HAVE INSPECTED CARBON SEAL FOR PROPER CONFIGN BY REFERRING TO THE AMM AND THE IPC AND CHK FOR AN O-RING. IDG INSTALLATION WAS COMPLETED AND SVCED PER AMM. PERFORMED SEVERAL ENG RUN-UPS PER AMM; IDG DISCONNECT CHK AND NO OIL LEAK NOTED. ALL IDG AND ENG INDICATIONS WERE NORMAL. ACFT X TOOK FLT ON SAME DAY. ACFT RETURNED TO ZZZ DUE TO LOW OIL QUANTITY AND PRESSURE INDICATION. DURING TROUBLESHOOTING; IT WAS OBSERVED THAT THE O-RING ON THE L ENG IDG CARBON SEAL WAS MISSING. THIS WAS IDENTED AS THE SOURCE OF THE OIL LEAK ON THE ENG. A NEW L IDG CARBON SEAL WAS INSTALLED PER AMM AND IPC TO CORRECT THE PROB. I WAS NOTIFIED BY THE ACFT MAINT DEPT MGR OF THE FINDINGS WHEN I RETURNED TO WORK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS ENGINE WAS ALREADY BEING WORKED AS A RESULT OF IDG PROBLEMS. DECISION WAS MADE TO PERFORM AN IN-FLIGHT SHUTDOWN PROCEDURE ON THE ENGINE TO CHECK FOR ANY PHYSICAL DISCREPANCIES IN THE ELECTRICAL WIRE BUNDLES AND ASSOCIATED HARDWARE AND CONNECTORS. MAINT ALSO DECIDED TO REPLACE THE IDG. PART OF THE REPLACEMENT OF THE IDG REQUIRES A NEW CARBON SEAL. REPORTER ALSO STATES WHEN HE WAS GIVEN THE NEW CARBON SEAL; HE DIDN'T NOTICE THE O-RING FEATURE WAS NOT PART OF THE CARBON SEAL. THEY PERFORMED TWO ENGINE RUNS AND OPENED UP THE ENG COWLS TO CHECK FOR OIL LEAKS; NONE WERE FOUND. THE ACFT DEPARTED AND RETURNED APPROX FIVE HOURS LATER WITH LOW OIL.

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.