Engine gear box seal replaced with routine post maintenance checks. Seal failed in-flight.

Attributes
ACN	305507
Time
Date	199505
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sfo
State Reference	CA
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	Other
Function	other personnel other
Qualification	other other : other
ASRS Report	305507
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other other : unspecified
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Aircraft of B-747 fleet had an idg removed from #4 engine during routine maintenance. While the idg was removed the seal between the idg and the gear box was replaced because of wear. After the idg was reinstalled and the engine had been closed an oil leak was detected under #4 engine. The engine was dry motored in the hangar and said to be ok for service. Any time a component such as an idg is removed or replaced, an engine run is required after it leaves the hangar and before being returned to service. An engine run was completed and no major oil leak was detected. After the aircraft was returned to service and left sfo, #4 engine had to be shut down in-flight and the aircraft had to return to sfo. When components such as an idg are removed or replaced, these components should be made to perform like they would perform in-flight, before they are returned to service. Callback conversation with reporter revealed the following information: reporter mechanic says that after the seal was replaced between the idg and the gear box, the engine was dry motored and checked ok. Then, before returning to flight, a 5 min idle check was made, still without any leak. However, the reporter thinks that a high power engine run should be made in order to put a greater load on the engine. Because, in this incident when in-flight the seal malfunctioned and the engine had to be shutdown.

Original NASA ASRS Text

Title: ENG GEAR BOX SEAL REPLACED WITH ROUTINE POST MAINT CHKS. SEAL FAILED INFLT.

Narrative: ACFT OF B-747 FLEET HAD AN IDG REMOVED FROM #4 ENG DURING ROUTINE MAINT. WHILE THE IDG WAS REMOVED THE SEAL BTWN THE IDG AND THE GEAR BOX WAS REPLACED BECAUSE OF WEAR. AFTER THE IDG WAS REINSTALLED AND THE ENG HAD BEEN CLOSED AN OIL LEAK WAS DETECTED UNDER #4 ENG. THE ENG WAS DRY MOTORED IN THE HANGAR AND SAID TO BE OK FOR SVC. ANY TIME A COMPONENT SUCH AS AN IDG IS REMOVED OR REPLACED, AN ENG RUN IS REQUIRED AFTER IT LEAVES THE HANGAR AND BEFORE BEING RETURNED TO SVC. AN ENG RUN WAS COMPLETED AND NO MAJOR OIL LEAK WAS DETECTED. AFTER THE ACFT WAS RETURNED TO SVC AND LEFT SFO, #4 ENG HAD TO BE SHUT DOWN INFLT AND THE ACFT HAD TO RETURN TO SFO. WHEN COMPONENTS SUCH AS AN IDG ARE REMOVED OR REPLACED, THESE COMPONENTS SHOULD BE MADE TO PERFORM LIKE THEY WOULD PERFORM INFLT, BEFORE THEY ARE RETURNED TO SVC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR MECH SAYS THAT AFTER THE SEAL WAS REPLACED BTWN THE IDG AND THE GEAR BOX, THE ENG WAS DRY MOTORED AND CHKED OK. THEN, BEFORE RETURNING TO FLT, A 5 MIN IDLE CHK WAS MADE, STILL WITHOUT ANY LEAK. HOWEVER, THE RPTR THINKS THAT A HIGH PWR ENG RUN SHOULD BE MADE IN ORDER TO PUT A GREATER LOAD ON THE ENG. BECAUSE, IN THIS INCIDENT WHEN INFLT THE SEAL MALFUNCTIONED AND THE ENG HAD TO BE SHUTDOWN.

Data retrieved from NASA's ASRS site as of July 2007 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.