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Old 21st Feb 2008, 00:57
  #209 (permalink)  
TheInquisitor
 
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swiss_swiss,

ref #191, previous type was C130. Yes, mainly mandraulic and clockwork, so perhaps no direct read-across.

Electrics were monitored for over / under freq (each phase), over & under volt (each phase and average across the 3). If memory serves, any phase drops below 70v or average drops to 90v across all 3, genny trips off. In the specific incident, 1 phase of a genny failed (4 EDGs supplying 4 seperate AC busses). That bus was powering the Aux Hyd pump, which was generating enough back EMF on the dead phase to keep the bus powered and prevent the genny tripping off. The problem only showed itself after the gear was raised and the Aux Hyd pump turned off.

Reason I thought it was worth a mention? It hadn't occurred previously, in some 40 years of ops. Indeed most operator's (myself included) immediate reaction was that such a scenario could not occur, yet once the problem was investigated it became clear that it could. It's an example of something nobody thought of, manifesting itself late in an ac's service life.

I appreciate that modern machinery is way more complex, however, and I imagine more closely monitored to boot - so still, may or may not have relevance! I'm sure 777 operators such as yourself could rule such a scenario in or out of possibility.
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