Shortly after take-off, the crew of the Boeing 747 aircraft received a number-four engine fire warning advisory. The crew actioned the non-normal checklist, secured the number-four engine, and discharged two engine fire bottles before the fire indication extinguished. The crew then jettisoned fuel and completed an uneventful landing at the departure airport.
Initial inspection by operator maintenance personnel revealed evidence of charring and discolouration around the engine combustion area. Maintenance personnel removed the engine from the aircraft and the engine was then test run on an engine test cell. The test run revealed a fuel leak from the left and right fuel manifold connectors. The connectors were confirmed as being secured with safety lockwire, but subsequent torque checks revealed a lower value of torque than that required by the engine manufacturer's maintenance manual. The fuel manifold connectors were re-torqued and another test run completed. The resulting test run at high power settings revealed no discrepancy. A decision was made by the operator to have the engine overhauled before being put back into service.
The operator's investigation reported that the number-four engine left and right fuel manifold connector attachments had been under torqued. The torque values, when checked, were as little as 80 inch pounds of torque instead of the correct value of 500 inch pounds. The engine had been last overhauled in August 1997. The connectors were documented as being correctly torqued and lockwired at that time. The only other documented maintenance in the area was completed during scheduled maintenance in May 2000, when a leak at one of the fuel nozzles was corrected. The area of the connectors is accessed on a regular basis for routine inspections, borescope inspections, and igniter plug changes. It could not be established why the connectors were under torqued.
The operator has issued an internal advisory memo to maintenance personnel highlighting the event and the relevant required procedures when torqueing the connectors.
|Date:||15 February 2001||Investigation status:||Completed|
|Time:||1848 hours UTC|
|Location:||15 km SW Bangkok, Aero.|
|State:||International||Occurrence type:||Fuel systems|
|Release date:||27 July 2001||Occurrence class:||Technical|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Bangkok, THAILAND|
|Departure time||1846 UTC|