747-400 Ballast Fuel and CG Questions
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747-400 Ballast Fuel and CG Questions
I have some questions regarding 747-400 system that I can not find answers to. I am hoping someone here has some Boeing documentations that they can forward to me with answers to my questions.
Regarding "Ballast Fuel": I often fly an empty BCF and we need about 8tons of ballast fuel in CTR tank to keep within the CG envelope for Take Off. The question is, can we burn this fuel in flight or should it be kept until landing?
Also, by inserting 8 tons in the FMC as Ballast Fuel, is it correct that the Fuel Logic will not let the scavange pumps scavange fuel out of the CTR tank below that level or is it just there to give a message when you have reached that number, so to turn CTR pumps OFF?
One Mechanic insists that you have to pull CB's for the scavange pumps in order to keep ballast fuel in CTR tank, but the other nite, we loaded 8tons in CTR tank, inserted 8tons in FMC "Ballast Fuel". CTR pumps were OFF all the way, since flight was only 5 hours. When we landed we still had 8tons in CTR tank. No scavange, No CB's pulled.
Also, is there anyway that someone could email me a CG and W&B work sheet for both the Freighter and the BCF.
I think my company might be using one for the Freighter instead of the BCF.
Thank you.
Regarding "Ballast Fuel": I often fly an empty BCF and we need about 8tons of ballast fuel in CTR tank to keep within the CG envelope for Take Off. The question is, can we burn this fuel in flight or should it be kept until landing?
Also, by inserting 8 tons in the FMC as Ballast Fuel, is it correct that the Fuel Logic will not let the scavange pumps scavange fuel out of the CTR tank below that level or is it just there to give a message when you have reached that number, so to turn CTR pumps OFF?
One Mechanic insists that you have to pull CB's for the scavange pumps in order to keep ballast fuel in CTR tank, but the other nite, we loaded 8tons in CTR tank, inserted 8tons in FMC "Ballast Fuel". CTR pumps were OFF all the way, since flight was only 5 hours. When we landed we still had 8tons in CTR tank. No scavange, No CB's pulled.
Also, is there anyway that someone could email me a CG and W&B work sheet for both the Freighter and the BCF.
I think my company might be using one for the Freighter instead of the BCF.
Thank you.
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CG-wise, you should be able to burn the ballast fuel after take-off, but depending on how you are dispatched, the company may not allow it. But look at the envelope on your weight and balance, and I've never see it exceed the flight CG by burning it. I have seen it go "below" the bottom of the envelope on an IAI converted plane, but that is because IAI just does not show the plane ever being that light.
CWT scavange logic is not armed unless CWT is burned down to a certain level, with 3200kg or below coming to mind. This is why you are told to operate the CWT pumps until the level is 1800kg or less on a normal flight, to then get below the level to trigger the scavange logic. So with ballast fuel, you have not done this, so it will not scavange.
As far as I know, entering the ballast fuel number into the FMC, if that software option is available, only creates the EICAS message for you to turn the CWT pumps off (assuming they were on) at that number, or prevents/inhibits the message on the ground or inflight of telling you to turn them on initially, in the case that you mention, nothing else. The CWT pumps will keep running, etc below the FMC entered number. So if you are using some of the CWT fuel as part of your planned fuel to start with, you need to "pad" the FMC number by a few hundred kg to actually end up having what you want as ballast by the time you get the EICAS msg and react to it, especially during the climbout......
All of the above assumes jet pumps, not the electric scavange pump, but it is probably the same logic.
CWT scavange logic is not armed unless CWT is burned down to a certain level, with 3200kg or below coming to mind. This is why you are told to operate the CWT pumps until the level is 1800kg or less on a normal flight, to then get below the level to trigger the scavange logic. So with ballast fuel, you have not done this, so it will not scavange.
As far as I know, entering the ballast fuel number into the FMC, if that software option is available, only creates the EICAS message for you to turn the CWT pumps off (assuming they were on) at that number, or prevents/inhibits the message on the ground or inflight of telling you to turn them on initially, in the case that you mention, nothing else. The CWT pumps will keep running, etc below the FMC entered number. So if you are using some of the CWT fuel as part of your planned fuel to start with, you need to "pad" the FMC number by a few hundred kg to actually end up having what you want as ballast by the time you get the EICAS msg and react to it, especially during the climbout......
All of the above assumes jet pumps, not the electric scavange pump, but it is probably the same logic.
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One Mechanic insists that you have to pull CB's for the scavange pumps in order to keep ballast fuel in CTR tank, but the other nite, we loaded 8tons in CTR tank, inserted 8tons in FMC "Ballast Fuel". CTR pumps were OFF all the way, since flight was only 5 hours. When we landed we still had 8tons in CTR tank. No scavange, No CB's pulled.
Do you ever use ballast fuel AND have fuel in the reserve tanks?
Originally, the hydromechanical scavenge pumps relied on fuel levels in the inboard mains and the CWT (and fuel pressure in the fuel feed manifold). There are float valves stopping these "jet" scavenge pumps from operating until the conditions are right. However, the float valves in the CWT may be wired open (modification), leaving only the wing tank float valves active. These wing float valves operate at 27,270 Kg (inboard main level). Jet pumps scavenge at a rate of 545Kg/hr. I don't know how you would stop the wing-only float valve scavenge system from operating.
There are a lot of airline/aircraft specific details here, so I would advise caution.
Rgds
NSEU
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Thanks for your input on the fuel system. I guess the Ballast fuel issue of "to burn or not to burn...that is the question" and it seams like we have 2 different camps on the subject.
Did anyone have a CG graph or W&B worksheet for the BCF?
Thanks again
Did anyone have a CG graph or W&B worksheet for the BCF?
Thanks again
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Just wondering if there are any current 747-400 combi operators using ballast fuel.
After the TWA explosion and prior to the new fuel management software/fuel system modifications, an AD was issued in 2002 telling the operators to turn off their CWT pumps prior to the pumps going low pressure. As a result, the scavenge system sometimes didn't work (the float valves in the CWT for the scavenge system didn't let the fuel into the scavenge at these higher CWT fuel levels).
A modification was carried out to the valves according to a Boeing Service Bulletin (keeping them open all the time) i.e. SB 747-28-2255 (Revision 2). This meant that only the fuel level in the main tanks inhibited the scavenge system. This mod, however, meant that any ballast fuel would be sucked out of the CWT. Combi operators would either have to inop their ballast systems (or deactivate their scavenge systems when ballast fuel was required).
These days, the Service Bulletin-modified aircraft still seem to be flying around (even after all the FAA required modifications to the fuel system). Do the combis still have their ballast systems inoped? (unless the scavenge system is deactivated)
Thanks
Rgds
NSEU
After the TWA explosion and prior to the new fuel management software/fuel system modifications, an AD was issued in 2002 telling the operators to turn off their CWT pumps prior to the pumps going low pressure. As a result, the scavenge system sometimes didn't work (the float valves in the CWT for the scavenge system didn't let the fuel into the scavenge at these higher CWT fuel levels).
A modification was carried out to the valves according to a Boeing Service Bulletin (keeping them open all the time) i.e. SB 747-28-2255 (Revision 2). This meant that only the fuel level in the main tanks inhibited the scavenge system. This mod, however, meant that any ballast fuel would be sucked out of the CWT. Combi operators would either have to inop their ballast systems (or deactivate their scavenge systems when ballast fuel was required).
These days, the Service Bulletin-modified aircraft still seem to be flying around (even after all the FAA required modifications to the fuel system). Do the combis still have their ballast systems inoped? (unless the scavenge system is deactivated)
Thanks
Rgds
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I guess the Ballast fuel issue of "to burn or not to burn...that is the question" and it seams like we have 2 different camps on the subject.
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BCF Aft CG Limit for landing
Hey ConnyCoba, did you get your W&B sheets?
I think you're on the right track. You need these sheets to determine the aft CG limit for landing....which also happens to be the aft CG limit for ZFW. That info will clearly demonstrate whether you are safe to land without the ballast fuel.
Not knowing your weights I cannot say for certain, but if my airline were to operate this aircraft empty with the standard 24,000lbs on landing and a dry operating index (DOI) of btwn 60~65 we would be well within the landing and ZFW envelope with no ballast fuel. However, the problem comes when you must taxi in. For this envelope the AFT limit comes a lot further forward, and may even put your empty and lightly fueled aircraft outside the limit without the ballast fuel.
So I agree with one of the repliers, use the ballast fuel in an emergency, but don’t plan on taxiing after landing. BTW, I checked the W&B sheets for the ERF and straight freighter and the result was the same. In fact the ERF was the most critical and would need the most ballast fuel.
I only have hard copies of the sheets so I can’t email them to you. Surely Cony supplies you with a sample sheet in the FM or a W&B manual onboard
Good Luck
I think you're on the right track. You need these sheets to determine the aft CG limit for landing....which also happens to be the aft CG limit for ZFW. That info will clearly demonstrate whether you are safe to land without the ballast fuel.
Not knowing your weights I cannot say for certain, but if my airline were to operate this aircraft empty with the standard 24,000lbs on landing and a dry operating index (DOI) of btwn 60~65 we would be well within the landing and ZFW envelope with no ballast fuel. However, the problem comes when you must taxi in. For this envelope the AFT limit comes a lot further forward, and may even put your empty and lightly fueled aircraft outside the limit without the ballast fuel.
So I agree with one of the repliers, use the ballast fuel in an emergency, but don’t plan on taxiing after landing. BTW, I checked the W&B sheets for the ERF and straight freighter and the result was the same. In fact the ERF was the most critical and would need the most ballast fuel.
I only have hard copies of the sheets so I can’t email them to you. Surely Cony supplies you with a sample sheet in the FM or a W&B manual onboard
Good Luck
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Sorry for posting a message on such an old message thread, gents. It's over two and a half years old, so I hope Conny did get an answer 
In the maintenance manual, Boeing does warn that leaving the scavenge system operative does run the risk of "in-flight loss of control". There are procedures for deactivating both the electric and hydromechanical pumps in the manual (12-11-5-003-053/-066).
Electric scavenging can be activated at 2 points:
1) when the CWT pumps are on and then go low pressure (not a problem when you leave a large quantity in the CWT for ballast)
2) when the reserve transfer valves open
It's not clear how even aircraft with modifications for carrying ballast can stop scavenging at the second point. For example, Combi ballast modifications appear to consist of only FMC and IDS software/wiring changes, not Fuel System Management changes.
These systems may simply rely on very little fuel being scavenged (in 2 hours) after the reserve transfer valves open.
The hydromechanical system is similar. Fuel transfer should only occur about the time the reserve valves open (but is controlled by float valves in the wing tanks). However, there is no time limit on scavenging with the hydromechanical system.
Rgds
NSEU
In the maintenance manual, Boeing does warn that leaving the scavenge system operative does run the risk of "in-flight loss of control". There are procedures for deactivating both the electric and hydromechanical pumps in the manual (12-11-5-003-053/-066).
Electric scavenging can be activated at 2 points:
1) when the CWT pumps are on and then go low pressure (not a problem when you leave a large quantity in the CWT for ballast)
2) when the reserve transfer valves open
It's not clear how even aircraft with modifications for carrying ballast can stop scavenging at the second point. For example, Combi ballast modifications appear to consist of only FMC and IDS software/wiring changes, not Fuel System Management changes.
These systems may simply rely on very little fuel being scavenged (in 2 hours) after the reserve transfer valves open.
The hydromechanical system is similar. Fuel transfer should only occur about the time the reserve valves open (but is controlled by float valves in the wing tanks). However, there is no time limit on scavenging with the hydromechanical system.
Rgds
NSEU
Last edited by NSEU; 4th Feb 2013 at 05:05.
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I believe that if the reserve transfer valves open during the flight, this is also a trigger for the electric scavenge pump to operate for 2 hours (or until the scavenge pump runs dry for 5 minutes). In this case, you would probably have to pull a CB. Mind you, my manuals say that the scavenge pump max output is 771Kg/hour, so it would take a while to shift 8 tonnes
Do you ever use ballast fuel AND have fuel in the reserve tanks?
Originally, the hydromechanical scavenge pumps relied on fuel levels in the inboard mains and the CWT (and fuel pressure in the fuel feed manifold). There are float valves stopping these "jet" scavenge pumps from operating until the conditions are right. However, the float valves in the CWT may be wired open (modification), leaving only the wing tank float valves active. These wing float valves operate at 27,270 Kg (inboard main level). Jet pumps scavenge at a rate of 545Kg/hr. I don't know how you would stop the wing-only float valve scavenge system from operating.
Do you ever use ballast fuel AND have fuel in the reserve tanks?
Originally, the hydromechanical scavenge pumps relied on fuel levels in the inboard mains and the CWT (and fuel pressure in the fuel feed manifold). There are float valves stopping these "jet" scavenge pumps from operating until the conditions are right. However, the float valves in the CWT may be wired open (modification), leaving only the wing tank float valves active. These wing float valves operate at 27,270 Kg (inboard main level). Jet pumps scavenge at a rate of 545Kg/hr. I don't know how you would stop the wing-only float valve scavenge system from operating.
Thanks
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Jet pumps and hydromechanical pumps are one and the same thing. They are fitted to later model 747-400s. They work using Venturi principles and have no moving parts apart from the float valves at the output and check (one-way) valves in the outlet plumbing. The motive force is provided by fuel flow in the main manifold (i.e. main pump-supplied fuel flowing to the engines). Because no electrics are involved, they are inherently safer than electric pumps.
One of the drawbacks of jet pumps is that, during maintenance when you need to remove small quantities of fuel from the Centre Wing Tank, you need to run an engine or APU to provide motive power. On the old electric type, you just flicked a switch on the overhead panel.
Hope this makes sense
Rgds
NSEU.
One of the drawbacks of jet pumps is that, during maintenance when you need to remove small quantities of fuel from the Centre Wing Tank, you need to run an engine or APU to provide motive power. On the old electric type, you just flicked a switch on the overhead panel.
Hope this makes sense
Rgds
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Hi NSEU,
To scavenge the centre on the hydromechanical style aircraft you don't have to run the engines or apu. You can just turn on the 2 and/or 3 main boost pumps and will achieve the same result.
Running the apu will also turn on these pumps automatically and also result in the same effect.
To scavenge the centre on the hydromechanical style aircraft you don't have to run the engines or apu. You can just turn on the 2 and/or 3 main boost pumps and will achieve the same result.
Running the apu will also turn on these pumps automatically and also result in the same effect.
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Ahh.... disregard... I just remembered the scavenge pump setup. There is flow. With the pumps on, and the manifold pressurised, fuel is forced through the venturies and back into the wing tanks (sucking up CWT fuel in the process).
Cheers
NSEU
Cheers
NSEU
