View Full Version : 777 Electrical System Questions...

31st Aug 2004, 22:07
Hi Guys and Gals,

Just to introduce myself, I'm not a real world pilot/engineer, but I am an avid aviation enthuiast and I'm building a fixed base 777 simulator at home, using Microsoft Flight Sim as a base package but with substantial bespoke enhancements.

I am writing my own software to try to bring some level of realism to the systems simulation and at present I'm working on the elecitrcal systems. I have access to a Flight Manual for the 777 , but have a number of questions regarding the electrical systems that are more detailed than the manuals I have cover.

I appreciate that this forum is primarily for real world participants, so please feel free to tell me to get off... or alternatively if there are any 777 engineers/pilots out there who would be prepared to assist me outside the forum in a one-to-one capacity then let me know.

Anyway, now that I've tried to be as honest as possible about my motives, on to the questions:

1. Starting from a completely cold and dark cockpit, with no power sources available, the Main Battery switch is pushed on.

Which busses and systems become powered?

2. Are there any cicrumstances in which a pilot input that de-selects a power source results in the loss of power to a bus even if the bus could be powered by an altermate source, or will the systems logic always select an alternate source if one is available?

3. According the the Flight Manual I have, the MFD Electrical synoptic display will show an amber crossed box for an engine generator control (as opposed to the engine generator drive) if the generator is "not supplying power or failed". Under what circumstances will the generator be "not supplying power" ?

1st Sep 2004, 00:02

Ill try to help you im a keen Flight simmer myself too, im a Licenced Eng on the 777/744 so ill blow the dust off my notes and try to answer your questions best i can.

Q1. Technically only the BATT No2 bus (Only has one Baterry, the bus is split into 2) , Standby power is automatic on the 777 from main batt bus, there is a manual switch but its on the maintenance panel and is not often used. Ill need to look the schematic for a fuller answer for you. With batt switch on all you see in the flight deck is 2 eng gen drive lights, the aircarft is dead otherwise.

Q2. off the top of my head No, the APU gen selection on the 777 is AUTO the switch remains in. When in the simulator on training we had many things failing, is takes some doing to kill this aircraft electrically! being a very electronic software driven aircraft power interuptions are not liked so its well designed to avoid them.

Q3 Need to check that one.

Its midnight when i answered this so sorry if it reads crap just finished shift!

Private MSG me your email.


gas path
1st Sep 2004, 13:24
Agree with FunctionedSatis, latching in the batt s/w just results in the (amber) gen. drive lights, if the standby power s/w is selected to batt. the static inverter will be powered, and power the standby a.c. bus but it's not normally used!
With engines running the electrical power is split left and right with the BTB's open. (all switches normally left latched in.)
Gen. failure results in amber drive light and amber cross on synoptic (‘drive’ shows for low oil pressure and /or failure), the BTB's will close and the remaining gen. will supply power to busses. If one of the BTB's (also) fails to close the backup gen. comes online to supply the now dead transfer bus. The main bus remains dead as does the affected utility bus.
Unlatching the gen. control s/w gives an amber cross on the 'gen control' on the synoptic.
Q3 Only if it is unlatched or the field is tripped. Just cycling the switch will bring it back online. Usually only occurs following something like a gen. change or engine change.

Also the BAT s/w only has an amber OFF light if selected off and there is AC power on the a/c.

Standby Power Switch

The standby power switch has these three positions:

OFF - AUTO - BAT (momentary).

On the ground, the off position makes the static inverter stay off. In the air, the off position has no effect.

The AUTO position puts the standby electrical power system under the ELMS control. A guard over the switch moves it to AUTO. The switch is normally left in AUTO.

To use the battery position (BAT). Push the battery switch on then open the guard and select BAT (push on release springs back to AUTO). With no AC power on the a/c, the switch in BAT turns the static inverter on and it powers the standby AC bus.
I think thats correct I had to sit and draw it out! :confused: