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[rattler]

I am sure this will be of interest to our AME's who are faced with keeping up with ever changing mods and the resulting  procedural changes.

[QUOTE]Report: Virgin Blue B73G near Rockhampton on Aug 13th 2007, fuel imbalance due to leak


By Simon Hradecky, created Tuesday, Apr 14th 2009 09:46Z, last updated Tuesday, Apr 14th 2009 09:49Z



The inserts remained attached to the bolts
(Photo: ATSB)  
A Virgin Blue Boeing 737-700, registration VH-VBR performing flight DJ-583 from Brisbane,QL to Hamilton Island,QL (Australia), was just reaching cruise altitude about 148km (80nm) from Rockhampton,QL, when the crew noticed a fuel imbalance due to loss of fuel from the right hand engine. The crew shut the right hand engine down and diverted to Rockhampton, where the aircraft landed safely.

The ATSB concluded in their final report, that the fuel imbalance and fuel loss was the result of a partial separation of the main fuel return pipe from the fuel/oil heat exchanger (FOHE). The separation was the result of the failure of all four internal threads on the FOHE due to being over-torqued, when the four attachment bolts were torqued beyond the 53 pound/inch specification for the particular modification state of the FOHE. The maintenance engineer was not aware of the different torque values for the various modification states of the FOHE. The level of supervision by the licensed maintenance engineer was affected by his involvement in other tasks.

During a routine walk around two days earlier an excessive amount of fuel was observed leaking from the right hand engine's fuel drain. The leak was traced to the engine driven fuel pump, which was replaced. For that purpose the fuel pump package was removed and the components, amongst them the FOHE, separated from the package.

The installation manual required a torque of 49-53 pound-inches (5.5-6.0 Newton-Meters) for the bolts connecting the fuel return pipe to the FOHE. However, when the maintenance engineer tightened the bolts, he used 60 pound-inches as permitted by a later modification state of the FOHE. No leaks were observed and the airplane was returned to service after the installation of the fuel pump package had been completed.

After the incident flight it was determined, that sufficient force had been applied to pull all four threaded inserts from the body of the FOHE.
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