B777- Ground Handling Bus.

[Haseen]

Dear:

How to supply Ground Handling Bus without energizing the whole electrical network with APU power only?

As per Training Manual if I keep the APU GEN switch on, the whole network will be powered. If I put the switch off, APU GEN GCU GCR opens, hence APU GEN is being de-energized!

Regards,

Haseen Ahmad
Bangladesh.

[tvrao]

If APU is running and quality of power is good and if you do not connect primary external power, then Ground handling relay automatically selects APU power to power the Ground handling bus.APB switch controls auxiliary power breaker and APU GCR.It does de-energize APU generator if APB switch is selected to OFF. To get power from APU generator you must have APB switch ON.
APU generator powers tie bus.From the tie bus left main bus and right main bus are powered through left BTB and right BTB.If you do not want power on main buses, select both BTB switches to ISLN, then both BTBs trip and now APU generator is powering only ground handling bus.

[spannersatcx]

my question would be: why?

[Haseen]

Book graphic shows a direct electrical connection from upstream of the APB. I would like to take advantage of not closing the APB the way I am doing in case of Primary External Power, not closing the PEPC(Primary External Power Contactor) and feeding Ground Handling Bus and again not handling the Bus Isol Switches.

[TURIN]

I'm with Spanners.

Why would you ever need to do that? :confused:

[Haseen]

Turin & Spanner:

It's difficult to resist the temptation once you see the electrical circuit!

[TURIN]

It's difficult to resist the temptation once you see the electrical circuit!

Are you saying that you are tinkering with a multi-million dollar aeroplane just for the fun of it? :eek:

If it isn't an AMM/FIM/MEL etc, procedure I don't do it. I tend to stay employed that way. :ok:

[Haseen]

Temptation doesn't have to be for fun only. It could be for learning either.
If the circuit diagram in the AMM is okay, it should work.

[TURIN]

Well yes, but you can, in theory select the landing gear to up while on the ground with no hydraulics on nothing should happen except perhaps the doors opening, but you wouldn't want to try it would you?

[763 jock]

I know nothing of the 777 but here's a thought. If you manage to get the APU running but somehow get the system configured so that only the GHB is powered, do you still have APU fire detection/extinguishers available?

[tvrao]

763j
APU fire detection /extinguishing systems operate from battery bus and they will be operational. when other buses are deenergized ,the batterybus2,hotbattery bus,battery bus remain powered.
Since APU needs fuel from aircraft tanks APU DC pump runs using battery bus2 power.ELMS also needs battery power. With so many electrical loads drawing power from battery ,the battery gets discharged fast .Since ground service bus is not powered ,no battery charging also.You do not have equipment cooling and you damage costly electronic boxes if you try to get only ground handling bus powered with APU running.
So the system is designed so that if APU is only available you can provide power to all buses including ground handling bus. This is to take care of non availability of ground power cart at some places.
In case of primary external power,the ground cart is providing the necessary AC power to the aircraft connector and you are not running any aircraft fuel pumps to get the external power. The only electrical control components involved in the aircraft are BPCU and few ground handling relays, so its safe to supply ground handling bus alone without powering other aircraft buses.
Eventhough the circuit diagrams look similar the design considerations are different, hence it is not a safe practice to power ground handling bus alone when taking power from APU .

[Dougie_diesel]

If the circuit diagram in the AMM is okay


Im pretty confident the circuit diagrams for the whole A/C are in the WDM somewhere, but what you're looking for is an AMM task like:
"TO SUPPLY APU POWER TO THE GROUND HANDLING BUS ONLY, DO THIS TASK...etc, etc"

Simulators are the time for "just to see what happens", not passenger carrying A/C.

I'm sure the B1/B2 in charge of this A/C would be able to find you an answer (forgive my assumption, of course, that it's not you).

[cedgz]

dougie diesel, you're a bit hard dude, don't assume that he's or not a b1/b2.
simple questions need simple answers, my answer would be "why would you just power the ground handling bus and nothing else with apu power, something wrong dude???"
and is is it possible to run #2 eng on the md11 without elec power(not starting)?, yes it is, if idg 2, apu and ext power craps out, and it's weird having a bat powered cockpit and hearing #2 running

[Dougie_diesel]

dougie diesel, you're a bit hard dude, don't assume that he's or not a b1/b2.



I DID say, forgive my assumption.

I DIDN'T say, he wasnt a B1/B2, just not the B1/B2 in charge of the A/C.

I know a lot of dual licensed engineers who are a LOOOOOOOONG way from holding a CRS approval!