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flibinite

Random failures question

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Checking to see if a recent 777 failure event was realistic or an anomaly. With random failures enabled (1 per 10 hours, no limit on count), I lost both primary and both secondary generators at once.  The RAM air turbine automatically deployed; I started the APU and got most power back.

 

A general question: Is this in fact a realistic failure scenario or more likely a quirk? A more specific question: As part of this event, I lost both port (left) side fuel pumps; presumable the APU/RAM combination would not power them. The port side tanks subsequently would not feed fuel even with all crossfeeds enabled.  Is this expected behavior in this type of event?

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Cool one :-)

 

Does sound like a fluke though.

 

You have two main generators and two backup generators = 4

For them to all fail at the exact same time ......pretty rare.

 

You could try and fail the two main generators manually in flight......if the backup generators again do not take over, but also fail than this is not programmed correctly.

 

The RAT automatically deploys if both AC transfer busses loose power.

So that was correct.

Starting the APU would in that scenario restore all power.

 

The engine and APU generators are the same.

Any combo of two of them can power all equipment.

With only one generator available (in your case the APU), automatic electrical load shedding will take place, starting with shutting down things like galleys.

Fuel pumps however would not be shut down (except one center tank pump can be load shed, but on the ground only!)

 

did you really get EICAS fail messages for the left/right and backup generator?

 

Or did you maybe have both left and right AC main bus failed (but all generators still working)?

Failed busses would support the fuel pumps on the left side not working if they were connected to those busses......but I dont know by hart where the fuel pumps are connected to (main bus/transfer bus/stby bus?).

 

Crossfeeding will not help you drain a tank.

If a tanks fuel pumps dont work then you cant pump the fuel out of it....no matter how many cross feed valves you open.

But what you DO accomplish by crossfeeding is that the tank that still has operating fuel pumps (in your case the right tank) can then supply fuel to the left engine to prevent it from failing.

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Wish I'd written the errors down, there were several. As I recall I had EICAS messages showing generator failures plus bus failures.  I recall the ELEC status page showed yellow "X" boxes for all 4 generators. Guess I'll chalk this one up to an anomaly, thanks for the detailed response.

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