Is anyone able to share or provide information on the Boeing 767-300ER electrical schematic other than what is shown in the AOM? In particular the standby electrical system
I guess a very remote situation / very bad day but I am interested to know if in the event you suffered a Dual AC bus failure would you be able to operate the Fuel jettison system in the case that you were very heavy and it would be desired to lighten your weight before landing.
I cannot seem to find anything in the manuals that say you would not be able to and it would seem strange that the situation of losing all AC sources whilst at the heavyweight was not considered a possible situation.

I don't know the specifics of this aircraft, but systems design can't cater for every possible scenario.

If you can't dump and must land ASAP, you land overweight. The aircraft is certified for such an operation. Same situation if the airplane has no fuel dumping capability.

No, I don't think so. Fuel boost pumps, to include the override/jettison pumps are AC pumps.

I just took a quick look at the WDM & the SSM. I know the standby inverter doesn't have enough ass to run an override pump, but I thought the HMG may. But, near as I can tell, at 0430 after being up 18 hours, the transfer bus doesn't carry the fuel pumps.

Remember, fuel systems are certified to to be able to supply fuel to the engines with the pumps off.

Update: I just looked at our training manual. It lists all the loads the HMG will carry and the fuel pumps* are not included.

*the DC APU pump can be powered by the HMG.

Do you have the QRH that supports the FCOM? If not you're just whistling in the dark.

There is no checklist for loss of both AC busses in the QRH.

pikachu wrote:

There is no checklist for loss of both AC busses in the QRH.

There is in ours. It says "Plan to land at the nearest suitable airport". Then it runs through a couple of engine procedures, and what to expect.

I'll look this up on My Boeing Fleet this weekend. I seem to recall that loosing both AC buess in effect trapped what ever fuel was in the CTR Tank, and thus could become a significant range issue.

I find it hard to believe that is Non Normal would in one operators QRH and not in another, assuming they are reasonably up to date?

BravoOne wrote:

I find it hard to believe that is Non Normal would in one operators QRH and not in another, assuming they are reasonably up to date?

The formatting of the QRH will make it a little difficult, but I'll see if I can do a little 'cut and paste' and put the appropriate section on here later tonight.

BravoOne wrote:

I seem to recall that loosing both AC buess in effect trapped what ever fuel was in the CTR Tank

I don't know. Yes, you can't rely on it being pumped out, but the aircraft will suction feed, and it should take it from where ever it's available. Maybe it'll come down to the weight (force) the fuel applies to the fuel feed inlet. Quite possibly, you'll burn fuel into an imbalance.

I'm going to study the fuel system schematic a bit when I get to work. An interesting intellectual/engineering question.

First I have to ask, Is this a scenario or has this really happeed? I worked with an on the B767-222 and -322 and never saw this in 33 years with them.
I would say the pilots would have to try and keep the landing long and smooth under 1.5G's and not worry about the overweight inspection to follow.
More important they get back safely to live to tell about it. It would have to be a catastrophic Failure for this to happen. And just Landing safely would and should be their Business at Hand.

strfyr51 wrote:

First I have to ask, Is this a scenario or has this really happeed? I worked with an on the B767-222 and -322 and never saw this in 33 years with them.
I would say the pilots would have to try and keep the landing long and smooth under 1.5G's and not worry about the overweight inspection to follow.
More important they get back safely to live to tell about it. It would have to be a catastrophic Failure for this to happen. And just Landing safely would and should be their Business at Hand.

I tend to agree but the designers and various authorities will still design the QEH to cover as many scenarios as possible. An overweight landing would be the last of my worries. If ou lost the CTR Tank pumps would not have the pumps used to pump the fuel to the fuel dump manifold and thus eliminate the fuel dump option?

fr8mech wrote:

The formatting of the QRH will make it a little difficult, but I'll see if I can do a little 'cut and paste' and put the appropriate section on here later tonight.

B767 NON-NORMAL
AC BUS OFF
MESSAGE: L AC BUS OFF, R AC BUS OFF
LIGHT: BUS OFF
CONDITION: THE AC BUS IS NOT POWERED.

This is followed by procedures to attempt and re-establish the lost bus(es) with the APU.

The procedures describes some of the conditions when either bus is inop. Then the statement:

If both BUS OFF lights stay illuminated:
Plan to land at the nearest suitable airport.

then:

If both engines are running:
EQUIP COOLING SELECTOR . . . . . . . OVRD
FLT DK TEMPERATURE CONTROL . . . . . MAN
NOTE: Inoperative Items (Both AC Buses Off).
Some pitot heat probes inoperative. [Flight in
icing conditions may result in some erroneous
flight instrument indications.]
All flight directors inoperative.
All autopilots inoperative.
Automatic speedbrake system inoperative.
[Manual speedbrake extension after landing is
needed.]
Anti-skid for outboard wheels inoperative.
Master caution system inoperative.
Do not use autobrakes.
Do not arm the speedbrake for landing.
The AC BUS OFF checklist is complete.

If an engine is inoperative:
AFT AND FWD FUEL XFEED SWITCHES . . . ON
EQUIP COOLING SELECTOR . . . . . . . OVRD
FLT DK TEMPERATURE CONTROL . . . . . MAN
NOTE: Inoperative Items (Both AC Buses Off).
Some pitot heat probes inoperative. [Flight in
icing conditions may result in some erroneous
flight instrument indications.]
All flight directors inoperative.
All autopilots inoperative.
Automatic speedbrake system inoperative.
[Manual speedbrake extension after landing is
needed.]
Anti-skid for outboard wheels inoperative.
Master caution system inoperative.
Do not use autobrakes.
Do not arm the speedbrake for landing.
The AC BUS OFF checklist is complete.
[END OF PROCEDURE]

So, the QRH does envision a dual bus failure, but doesn't talk about fuel pumps at all.

BravoOne wrote:

I seem to recall that loosing both AC buess in effect trapped what ever fuel was in the CTR Tank, and thus could become a significant range issue.

So, as I expected, the engines will suction feed through a bypass valve installed in the wing tanks. But, there are no bypass valves installed in the center tank. The fuel is trapped and becomes unusable.

strfyr51 wrote:

First I have to ask, Is this a scenario or has this really happeed? I worked with an on the B767-222 and -322 and never saw this in 33 years with

Agreed. I've got 32 years working both the B757 & B767, and haven't seen a dual bus failure, at least not one where they haven't been able to re-establish at least one bus. But, an interesting exercise to run through.

Lpbri wrote:

https://en.m.wikipedia.org/wiki/Gimli_Glider

That was not a dual AC Bus failure. What does it have to do with this thread?

Yes there is a QRH procedure written by Boeing for this.

The probability of a dual AC Bus Failure has to be out outrageously low.

BoeingGuy wrote:

The probability of a dual AC Bus Failure has to be out outrageously low.

I seem to remember an AA 767 that was traversing left to right coast and had a dual bus AC bus failure and diverted to ORD.
The reason I remember is that the batteries had run down to the point that there was not enough capacity left in them to close the fuel valves to shut down the engines after landing at ORD.
They had to wait until MX got to the aircraft and manually closed the valves in the pylons.
**********
I just do not remember enough details to pull up a search.


Okie

strfyr51 wrote:

First I have to ask, Is this a scenario or has this really happeed? I worked with an on the B767-222 and -322 and never saw this in 33 years with them.
I would say the pilots would have to try and keep the landing long and smooth under 1.5G's and not worry about the overweight inspection to follow.
More important they get back safely to live to tell about it. It would have to be a catastrophic Failure for this to happen. And just Landing safely would and should be their Business at Hand.

Agreed and I think you would have to be having a really bad day for that to even happen in that sort of combination. But, no I have not heard of this ever happening.

As has been said, if you need to land overweight then so be it.

Was just thinking of the scenarios where we might take off at Max Take Off Weight (412,000 Lbs) and then suffer a dual AC Bus Failure.

Very remote indeed but just wondered if it was considered such a remote scenario that the CTR fuel pump functionality is not even mentioned in our QRH Non-Normal checklist fro the dual AC Bus

I was wrong as there are dedicated fuel jettison pumps within the CTR tank, therefore the loss of both Left and Right AC busses would not prevent fuel jettison. Operating on suction fuel feed appears to be dicey at high altitude, or high power settings.

BravoOne wrote:

I was wrong as there are dedicated fuel jettison pumps within the CTR tank, therefore the loss of both Left and Right AC busses would not prevent fuel jettison. Operating on suction fuel feed appears to be dicey at high altitude, or high power settings.

Not on ours. We have 2 override pumps in the center tank. A loss of AC power will make those pumps, along with the boost pumps in the left and right tanks, inoperative.

And, near as I can tell from the schematic and D&O, we have a bypass pickup in the main tanks, but none in the center.

Those dedicated pumps you write about, where do they get their power in the absence of AC?

It does not say what power the jettison pumps in the document I'm looking at (FCOM). Being that the FCOM is not as detailed as your Maint manuals one could assume you are correct. It's been awhile since I had anything to do with the 767 (-200ER), that my memory fails me on those details. Having "technical issues" with MBF this morning so I'll have to wait until tomorrow for anything meaningful to contribute.

Final correction. The CTR tank override boost pumps are in fact the same as the ones used for fuel jettison. Sorry for the confusion X$#@

Okie wrote:

BoeingGuy wrote:

The probability of a dual AC Bus Failure has to be out outrageously low.

I seem to remember an AA 767 that was traversing left to right coast and had a dual bus AC bus failure and diverted to ORD.
The reason I remember is that the batteries had run down to the point that there was not enough capacity left in them to close the fuel valves to shut down the engines after landing at ORD.
They had to wait until MX got to the aircraft and manually closed the valves in the pylons.
**********
I just do not remember enough details to pull up a search.


Okie

Couldn’t they have just pulled the fire handles?.

GF

BravoOne wrote:

I was wrong as there are dedicated fuel jettison pumps within the CTR tank, therefore the loss of both Left and Right AC busses would not prevent fuel jettison. Operating on suction fuel feed appears to be dicey at high altitude, or high power settings.

The pumps in the center wing are actually dual purpose Override/Jettison pumps. In normal flight they supply more pressure (override) than the wing fuel pumps so fuel is used from the center wing before fuel is used from the wing tanks.

When fuel is jettisoned, the only thing that happens is the jettison valves are opened and allow fuel to be pumped overboard from the center tank if the Override/Jettison pumps are operating. There are no separate pumps for jettisoning fuel.

GalaxyFlyer wrote:

Couldn’t they have just pulled the fire handles?.

Normally Open Valve, it takes electrical to close the valve. (fail safe in the run condition) The battery had been drained dead. Cable and linkage days are behind us.

Same issue with the QF32 when the Roller came apart at the seams. The devastation of the number two engine, primarily from the turbine or secondary the short term fire damaged the electrical to the #1 and they could not shut it down when they finally made it to terra firma.
There were pictures of the AFC pumping water, foam and anything else they could toss into the #1 engine for 20 minutes or so before they snuffed out the core and shut it down.

If I get time I will try and search the incident about the 767, it was discussed on a thread here at A nut. I do not remember the exact cause but there was either a step missing in the "what happened book" QRH that caused the pilots to incorrectly configure because of a problem or something along those lines that ended up with zero electrical after the battery finally totally discharged.

Okie

Couldn’t they have just pulled the fire handles?.

But there was no juice left in the battery. The LP cocks come off the hot battery bus.
The hot battery bus can only be fed by the battery, not by the DC busbars.
The B777 has special little LP cock batteries to get round this.

Well, I am an old fashioned guy, shut down the C-5 a couple of times by pulling the handle.

GF

Well sure, the Devil is in the details. If you apply stone age operating procedures to a modern aircraft it could spell disaster when something goes wrong. For any era aircraft, understanding how the systems works has to be job one if you are going to have to deal with non standard emergencies. 99.9999% of the time, the fire handles would S/D a modern aircraft.

On the 787, there is only one physical circuit breaker in the cockpit. It is for backup power to shut down the engines and APU if all of the aircraft buses fail. Just one small detail that could ruin your day if you didn't understand the existence, function and the reason for that specific redundancy. So if that circuit breaker was not pushed in or was tripped, with complete loss of electrical buses you could not shut down the engines or APU.