B777 ETOPS

[HighSpeed]

Hi,

I would like to find out about your company's ETOP procedure regarding lost of 2 main elec supply on the B777 prior to ETOPs Entry Point (ETOPS segment)?

At our company, we operate using single MEL/DDG and despatch with 1 elec sys U/S, you are limited to 120 mins. What if you are despatch with this config and lose another elec sys in flight prior entering ETOPS segment?

As it's not clearly spelt out in our books, I would like to find out your views regarding the legality of continuing the flight. Personally, I fell the aircraft is no longer ETOPs worthy.

Thanks.

HS

[Elevation]

If memory serves me right, the non-normal checklist states that in case of losing 2 main AC source, land ASAP.
Looking at Volume 2 of B777 manual, it defines main AC source as APU, and both engines' IDG.
So in answering to your question, yes, you should in fact land ASAP if only 1 main AC power source remains.

[HighSpeed]

elevation,

but the BUG sys (backup gen) constitute another sys. therefore, the b777 have 4 elec sys, that's where my dilemma starts...

HS

[Elevation]

Highspeed,
I am typing this from memory (and I my memory has not been very good lately ;)), the 777 manual volume 2 as I remember it cleary stated that the 2 IDG and APU are the main AC power systems.
It has no mention of the BUG being a main AC power system.
So as they say, "in the subsequent court of enquiry" you will be grilled, toasted, deep-fried to charcoal bits by this little smart-ass lawyer trap.

[Elevation]

Highspeed,
Now with the books in front of me, I see you dilemma....
In Volume 2, it is stated that,
"The main AC electrical power sources are :
-left and right IDGs
-APU generator
-primary and secondary external power."

BUG is discussed in a seperate paragraph, and no mention of it being a MAIN AC ELECTRICAL POWER.

In the QRH,
"There are some situations which always require landing at the nearest suitable airport.......
-one main AC power source remaining (such as engine, APU or backup generator)
......."

So therein lies the confusion, but if I am in the situation that you have mentioned, I would play it safe and land at the nearest suitable airport.

[Flight Safety]

Someone please correct me if any of this data is wrong.

Both engine IDGs and the APU Gen can supply 120kva each. Any one of these three power sources alone, is capable of supplying all of the power needs of the entire aircraft. The RAT Gen can supply only 7.5kva and only supplies power to the standby systems.

I don't have very complete info on the backup Gens, and this to me seems an important area for this discussion thread. I don't know what their power output is, but they do feed DC power into 400Hz AC converters, so they can supply AC power. I just don't know HOW MUCH AC power they can provide. This to me seems an important question to answer, as to whether you would dispatch or not by considering whether to regard the back Gens as primary AC power sources (surely the manuals indicate this). My guess would be that the backup Gens can supply AC power with some load shedding, but may not have enough AC power available to supply the entire aircraft. If this were the case, you probably could not consider these as primary AC power sources in making the MEL and ETOPS dispatch decisions.

I do know that the backup Gens are considered the primary DC power sources for the flight controls, but I could do with more data on the backup Gens.

Assuming then that the Backup Gens are NOT considered primary AC power sources, and you dispatch (ETOPS=120), here are your scenarios.

Suppose you dispatch with the APU Gen INOP, and you lose one of the IDGs. By the manual your flight is over (in or out of the ETOPS segment), and you land at the nearest suitable airport.

Suppose you dispatch with one IDG INOP (with the APU shutdown in flight), and you lose the other IDG. You have more drama here as I assume the Backup Gens will supply some load shedded AC, while you get the APU fired up and its Gen online. Again your flight is over (in or out of the ETOPS segment), and you land at the nearest suitable airport.
------------------
Safe flying to you...


[This message has been edited by Flight Safety (edited 20 March 2001).]

[gas path]

The back-up generators are rated at a maximum of 20kva they are variable speed variable frequency generators with their output fed (via the converter to make it satisfactory a.c. power) to their respective transfer bus during non normal conditions and during autoland.
They come on-line during engine start for 15 secs as a form of confidence test.
I think that if one IDG is inop. dispatch is with the remaining IDG feeding it's respective bus, and the APU Generator feeding the inop. IDG bus. (ETOPS 120mins??)
Failure of the APU or the 'good' IDG will result in the BUG coming on-line feeding it's transfer bus ie. flt. instruments etc. as already stated.
Land at the nearest suitable airfield!!
Hope that helps!


[This message has been edited by gas path (edited 20 March 2001).]

[MasterGreen]

All correct above by my reasoning. The BUGs are BackUp Gennies only. 3 Full A/C sources (1 per engine + APU) required for 180+ ETOPs (plus the BUGs). 2 A/C sources for 120 minutes (BUG requirements seem to vary depending upon local tastes). Down to 1 A/C source (regardless of BUG status) - land ASAP.

There is another (small) DC generator on the RAT also (B777) for those really desperate moments.

MG




[This message has been edited by MasterGreen (edited 25 March 2001).]

[777AV8R]

Maybe this will help out as well.
Any 2 main generator sources will provide all power necessary for the aircraft. That being 2 IDGs or an IDG and APU.
The backup generators will come on line for only these reasons: 1. Testing after engine start 2. Only 1 generator including APU available, 3. Power to one or both main AC buses lost, 4. APP mode selected.

Normally when an aircraft is degraded to one available main system output, whether it be electrical or hydraulic, land at suitable airport will be the requirement.

There are certain requirements for dispatch under MEL for ETOPS and the MEL clearly defines what system components are required electrically. Unfortunately, I don't have my MEL book here as I write, so I can not be specific about the 120 / 180 rule. Suffice to say, the backup generators are there only for back up purposes and I believe dispatch with a back up alone and no APU will disallow ETOPS. It is there for strictly back up purposes.
The RAT is not a main source of power, in fact, the RAT will look after hydraulic requirements first before any electrical, thus, the system will shed electrical to provide hydraulic power for the aircraft components. The RAT provides 1/10th the power of an IDG.

Hope it helps

[HighSpeed]

thanks guys for all your opinions. as Elevation had explained, boeing's QRH 'claim' the BUG system as an AC source. from what i understand from that, if you have one main AC plus the BUG system, there is NO need to land ASAP !!

boeing is quite clever by making things muddy !! as i mention, we operate using a single MEL/DDG. i believe certain company opt to have a non-ETOPS MEL/DDG and an ETOPS MEL/DDG, i would be interested to know what their MEL/DDG says.

HS

[Elevation]

Highspeed,
It is true that only 1 of the 3 main AC source (IDG or APU gen) is needed to power the whole a/c electrical need.
As I have said, the ops manuals 2 do not say the BUG is a main AC source. It is only "mentioned" in the non-normal checklist pre-amber as a "main AC source".
Like what 777AV8R said, in any situation, with only 1 of 3 MAIN system remaining, land ASAP. The BUG is exactly what it said it is, a BACK-UP gen, not a main.
Happy flying.

[Checkboard]

As an aid to the discussion: my company operates 737 and 767 aircraft on ETOPS. As ETOPs requires backup electical power, the 737 must have the APU operating throughout the ETOPs portion of the flight (not having a backup system.)

The 767 has a backup (hydraulic ?) generator, and thus doesn't need to have the APU operating, but I would assume it must be serviceable. In this case it would appear that the backup generator is considered a viable alternate power source.

In the same vein as the 737 has only one fuel transfer valve, that valve must be exercised (i.e. opened and closed) in cold soak conditions before the ETOPs portion of the flight. As the 767 is fitted with two fuel transfer valves, it isn't subject to this requirement.

[Flying_Steph]

By the way...
How many ETOPS minutes do you have on the B777 ? At least 180, I guess...

200-somehting ?
Thks in advance !

[HighSpeed]

we are currently operating only 120 mins ETOPS but the 180 mins is undergoing evaluation and i believe we will be operating 180 mins in a month or two. ours are RR powered...

HS