Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
convair880mfan
Topic Author
Posts: 253
Joined: Fri Jun 25, 2021 12:33 am

Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 7:21 pm

I've read about some airliners that carry fuel beneath the passenger cabin in order to give them added range. Is that dangerous, for example, in the event landing gear fails to extend and the plane is forced to make a belly landing.

Also . . . do airliners that carry fuel in the horizontal stabilizer . . . does this pose a potential fire danger to the flight records carried back there?
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 7:44 pm

It’s designed into the planes, called center wing tanks. Fuel is also stored in some stabs, B747 for example. We had a 2200# fuel tank about 3 feet from the recorders in a Global.

A gear up landing would be done with the CWT empty
 
User avatar
fr8mech
Posts: 8392
Joined: Mon Sep 26, 2005 9:00 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 8:07 pm

Center wing tanks are common. The B747 holds a ridiculous amount of fuel in the center tank. The -400 can carry something like 115,000 lbs…maybe more. Both the B757 and the B767 have a center tank…sometimes referred to as the Center Aux tank. Something like 45K & 60K, respectively. Even the B727 had a center (#2) tank…25’ishK?
 
convair880mfan
Topic Author
Posts: 253
Joined: Fri Jun 25, 2021 12:33 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 9:12 pm

Is the fuel from the center fuel tank used first? If not, during a wheels up landing, is the center tank fuel the first to be jettisoned before landing?

I wonder if center fuel tank fires have caused a lot of fatalities and injuries that would not have happened if fuel was only kept in the wing tanks. Guess it isn't financial feasible to not have center tanks. Any aircraft without those center tanks?

Thanks for all your responses. I knew the 727 had center tanks but forgot. Because of the TWA 747 explosion over the Long Island area I knew it had a center tank. I think some aircraft manufacturers even offer an additional tank in part of the cargo compartment. Could be wrong though.
 
113312
Posts: 704
Joined: Sat Apr 16, 2005 9:09 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 9:29 pm

Most aircraft have centerwing tanks. They may be main tanks or auxiliary tanks. Your concern about the location of that fuel and the remote possibility of a belly landing are overblown. The structure of the wing spar carrythrough is about the strongest part of the aircraft. A full gear up landing in an airliner is exceptionally rare. Fuel utilization varies with the type of aircraft. On some types, center/aux tanks will be empty on most flights except the longest range needed. IN other types, the center tanks will never be empty. With regard to TWA 800, the cause of the explosion remains controversial. It most certainly was not caused by the electrical fuel pumps as all electrical components of those pumps are not actually in the tank.
 
bluecrew
Posts: 122
Joined: Sun Apr 20, 2014 3:13 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Oct 25, 2021 11:42 pm

convair880mfan wrote:
Is the fuel from the center fuel tank used first? If not, during a wheels up landing, is the center tank fuel the first to be jettisoned before landing?

I wonder if center fuel tank fires have caused a lot of fatalities and injuries that would not have happened if fuel was only kept in the wing tanks. Guess it isn't financial feasible to not have center tanks. Any aircraft without those center tanks?

Thanks for all your responses. I knew the 727 had center tanks but forgot. Because of the TWA 747 explosion over the Long Island area I knew it had a center tank. I think some aircraft manufacturers even offer an additional tank in part of the cargo compartment. Could be wrong though.

1. Yes. Specific usage restrictions apply depending on type - most relevantly the 737 has restrictions on when the center fuel pumps can be on based on how much fuel is in the tank and what stage of flight, due to an FAA Airworthiness Directive. Generally speaking the center tank is drained first in most transport category aircraft.

2. No, they haven't. Notably, China Airlines 120 went up in a blaze due to a punctured wing tank.
Your 737 or A320 won't get very far without a center tank, you just can't feasibly carry that much weight on the wings. Also... if the wing tank goes up, that's just as catastrophic. Any fuel fire is going to cause the same catastrophic danger to the airplane.
Smaller aircraft don't carry anything under the fuselage, think ATR and Dash 8. Even the E190, though it's considered "left" and "right" fuel tanks, has the bulk of the capacity located where you'd have a "Center" tank, you just have a left and right fuel system and the tanks are divided in the middle.

3. The 727 did indeed have a 27,800lb center fuel tank. The 727 is a little different, it was #1, #2, #3.
The Airbus has the option of "ACT"s, Additional Center Tanks, to enhance its range, available on the 319, 320, and 321, but I've only heard of it being installed on the A321. They really give the A321 the legs it needs to be equivalent enough to a 757's capabilities, mainly transcontinental US flying without worrying about weight restrictions or particularly bad winds during cruise.
The TWA 800 story is a tragedy, but whatever the cause, it would have happened the same way in a wing tank versus the center fuel tank. Freak accident really... empty fuel tank creates a fuel air mixture, essentially a fuel air bomb, and the NTSB's conclusion was it *likely* was caused by a short traveling through a wire for the fuel quantity indicator. Seems possible enough, but I think you'll find plenty of people in aviation that never really believed that.
 
User avatar
Starlionblue
Posts: 20867
Joined: Fri Feb 27, 2004 9:54 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 4:01 am

convair880mfan wrote:
Is the fuel from the center fuel tank used first? If not, during a wheels up landing, is the center tank fuel the first to be jettisoned before landing?

I wonder if center fuel tank fires have caused a lot of fatalities and injuries that would not have happened if fuel was only kept in the wing tanks. Guess it isn't financial feasible to not have center tanks. Any aircraft without those center tanks?

Thanks for all your responses. I knew the 727 had center tanks but forgot. Because of the TWA 747 explosion over the Long Island area I knew it had a center tank. I think some aircraft manufacturers even offer an additional tank in part of the cargo compartment. Could be wrong though.


Centre fuel tank fuel is used first, but not for fire hazard reasons. You want to use wing fuel last in order to alleviate wing bending and stress on the wing/body join.

I think you're way overestimating the risk of having centre tanks and stabiliser tanks.

If the impact is so hard it crumples the lower fuselage structure, you have more problems than just leaking fuel. Plus your wing tanks are most likely at risk as well. Jet fuel is also not as flammable as one might think. It needs to be atomised to ignite. There have been incidents where evacuating pax had to walk through big puddles of fuel, but there was no ignition.
 
convair880mfan
Topic Author
Posts: 253
Joined: Fri Jun 25, 2021 12:33 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 5:52 am

Thanks to everyone who responded. I learned a lot. Thinking about what the others have written here made me think that if center fuel tanks were dangerous, the FAA and the aviation authorities of other countries would not allow them in commercial aircraft.

I am also thinking now that I am not aware of any cases of aviation accidents involving aircraft with tanks in the horizontal stabilizer where those tanks caused fires that destroyed flight recorders. I don't know which aircraft have tanks in the horizontal stabilizer but I think I read that the 747-400 and the MD-11 have them. Don't know about the 747-8.
 
User avatar
Aaron747
Posts: 16572
Joined: Thu Aug 07, 2003 2:07 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 6:07 am

convair880mfan wrote:
I don't know which aircraft have tanks in the horizontal stabilizer but I think I read that the 747-400 and the MD-11 have them. Don't know about the 747-8.


That information is quite easy to obtain via Google.
 
User avatar
Horstroad
Posts: 613
Joined: Thu Apr 08, 2010 8:19 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 6:20 am

The center wing tanks usually are the largest. On the 777 (-200LR/-F/-300ER) for example the center tank holds 184,480lb and the wing tanks 69,630lb each. I think some early versions of the 777 didn't use the space in the center wing box for fuel. The two compartments of the center tank in the wings were connected by a pipe.


Some aircraft have fuel in a tail tank in the horizontal stabilizer, but the amount is usually pretty small compared to the overall capacity of the tanks. It's mainly used for CG optimization during flight. I's usually used up before landing.


The MD-11 has a bladder tank below the center wing box, the lower aux tank. This fuel is used first. Second is the fuel in the upper aux tank (the largest tank of the MD-11). That's the tank other manufacturers call the center tank. It's the center wing box inside the fuselage. When both aux tanks are empty, fuel from main tank #2 is used. Of all three main tanks it is the largest. It sits in the wing roots of both wings and both compartments are connected by a pipe which goes through the upper aux tank. Other manufacturers would have the #2 tank and upper aux tank together as one center tank. When the tank #2 has reached the same quantity as tanks #1 and #3, fuel transfer between the tanks stops. Now each main tank just feeds one engine without any more transfer. Last step of the fuel schedule is transfer of fuel from the tip compartments of tanks #1 and #3 to their respective main compartments, when the quantity in each main compartment drops below 5000lb.
Edit: when I say "fuel is used first" I mean the tank is emptied first. The engines are always fed by their respective main tanks. But a soon as the level in the main tank drops, they are topped of by transferring fuel from the other tanks. Lower aux transfers to upper aux, upper aux transfers to #1, #2 and #3. #2 transfers to #1 and #3.

When there's more than 60,000lb fuel on board, the tail tank is used for CG control. As soon as the fuel level drops below 51,000lb the tail tank is no longer used. All fuel from the tail tank is moved forward once the aircraft descends below 19,750ft.

While the MD-11 uses this rather complicated fuel schedule controlled by valves and pumps commanded by the Fuel System Controller and the Ancillary Fuel System Controller, the B777 simply uses stronger center tank pumps to overpower the main tank pumps to use that fuel first.


Usually no fuel leaks at all are permitted on fuel tanks inside the pressurized areas.


Always think like that: If it was dangerous, it wouldn't have been certified.
 
User avatar
Starlionblue
Posts: 20867
Joined: Fri Feb 27, 2004 9:54 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 7:56 am

convair880mfan wrote:
Thanks to everyone who responded. I learned a lot. Thinking about what the others have written here made me think that if center fuel tanks were dangerous, the FAA and the aviation authorities of other countries would not allow them in commercial aircraft.

I am also thinking now that I am not aware of any cases of aviation accidents involving aircraft with tanks in the horizontal stabilizer where those tanks caused fires that destroyed flight recorders. I don't know which aircraft have tanks in the horizontal stabilizer but I think I read that the 747-400 and the MD-11 have them. Don't know about the 747-8.


Flight recorders are pretty sturdy. They're also not in the stabilizer but significantly further forward.

Again, there's this impression that aircraft fuel tanks are close to exploding at any moment if proper precautions are not taken. That is very far from the truth.

For completeness, the A330/A340 has a stabilizer tank for CG control in the cruise.
 
User avatar
thebunkerparodi
Posts: 116
Joined: Sat Aug 29, 2020 8:45 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 9:08 am

no and it's safer now thanks to the reccomandations issued after TWA 800 and philippines airlines 143
 
zanl188
Posts: 3882
Joined: Sat Oct 21, 2006 9:05 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 11:50 am

What is the a.net consensus regarding tank inerting systems?
 
Woodreau
Posts: 2175
Joined: Mon Sep 24, 2001 6:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 12:57 pm

It’s there. There’s nothing the pilots can do about it. It operates without pilot interaction. Pilots can’t turn it on or turn it off. All they can do is call maintenance if there is an ECAM or EICAS message about it.

Regarding stabilizer fuel tanks I’ve heard that one airline asks during the tech interview what the difference is between the stab tank on a 747 vs the stab tank on a 330/340. One is used merely as fuel storage. The other actively used to manage CG in flight. Is the gist of it.
 
User avatar
77west
Posts: 1042
Joined: Sat Jun 13, 2009 11:52 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 6:33 pm

Of course we can also bring Concorde into this discussion with its 14 or so separate fuel tanks and complex fuel management / CG system
 
phatfarmlines
Posts: 2041
Joined: Thu Sep 27, 2001 12:06 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Tue Oct 26, 2021 8:32 pm

convair880mfan wrote:
I've read about some airliners that carry fuel beneath the passenger cabin in order to give them added range. Is that dangerous, for example, in the event landing gear fails to extend and the plane is forced to make a belly landing.

Also . . . do airliners that carry fuel in the horizontal stabilizer . . . does this pose a potential fire danger to the flight records carried back there?


We learned from SQ006 that, yes, having fuel in the center tank can be dangerous. Probably the only crash where survivors were in the front and rear of the plane.
 
User avatar
Starlionblue
Posts: 20867
Joined: Fri Feb 27, 2004 9:54 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 12:00 am

phatfarmlines wrote:
convair880mfan wrote:
I've read about some airliners that carry fuel beneath the passenger cabin in order to give them added range. Is that dangerous, for example, in the event landing gear fails to extend and the plane is forced to make a belly landing.

Also . . . do airliners that carry fuel in the horizontal stabilizer . . . does this pose a potential fire danger to the flight records carried back there?


We learned from SQ006 that, yes, having fuel in the center tank can be dangerous. Probably the only crash where survivors were in the front and rear of the plane.


There will always be edge cases like that. Aircraft designers can't predict and cater for every possible scenario, in this case including trying to take off from the wrong runway when it was occupied with construction equipment.
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 12:30 am

The only large planes I can think without center fuel are the C-130, C-141 and C-5. The C-17 added fuel in the wing box as a cut-in during production—60,000#, I think. They needed the range. I don’t think the Gulfstreams have center fuel, either.
 
User avatar
Starlionblue
Posts: 20867
Joined: Fri Feb 27, 2004 9:54 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 7:58 am

GalaxyFlyer wrote:
The only large planes I can think without center fuel are the C-130, C-141 and C-5. The C-17 added fuel in the wing box as a cut-in during production—60,000#, I think. They needed the range. I don’t think the Gulfstreams have center fuel, either.


The A380 has no centre fuel tank. It was planned for the -900 and the -800F but never installed on the -800.

The centre tank is a customer option on the A330.
 
Redbellyguppy
Posts: 257
Joined: Sat Apr 01, 2017 3:57 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 8:14 am

You’re only going to get 17000 lb onto a 737 if you can’t use your center tanks, out of a potential capacity around 46,000 lb.
 
Max Q
Posts: 9126
Joined: Wed May 09, 2001 12:40 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 9:13 am

GalaxyFlyer wrote:
The only large planes I can think without center fuel are the C-130, C-141 and C-5. The C-17 added fuel in the wing box as a cut-in during production—60,000#, I think. They needed the range. I don’t think the Gulfstreams have center fuel, either.



Isn’t that center fuel tank on the C17 clearly visible above the cabin ?
 
Tristarsteve
Posts: 3706
Joined: Tue Nov 22, 2005 11:04 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 11:26 am

The Airbus has the option of "ACT"s, Additional Center Tanks, to enhance its range, available on the 319, 320, and 321, but I've only heard of it being installed on the A321


Qatar Airways has two A319 aircraft fitted with an ACT.
They have provisions for six ACT which would fill up both holds, but when I worked on them only one was used, at the front of the rear hold.
We used to send it from ARN to DOH and put fuel in the ACT often. The aircraft had a standard cabin with lie flattish seats in business class and the passenger bags filled the rest of the holds.
I assume the aircraft were bought as business jets? but used by the airline.
 
LCDFlight
Posts: 1368
Joined: Wed Jan 01, 2020 9:22 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 2:19 pm

If the fuselage tank catches fire, this could be deadly to passengers. However, a fire in a wing tank would also be quite hazardous, at least as I picture it.
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 3:20 pm

Max Q wrote:
GalaxyFlyer wrote:
The only large planes I can think without center fuel are the C-130, C-141 and C-5. The C-17 added fuel in the wing box as a cut-in during production—60,000#, I think. They needed the range. I don’t think the Gulfstreams have center fuel, either.



Isn’t that center fuel tank on the C17 clearly visible above the cabin ?


It is, I don’t know if the tank was adapted or the wing designed to accommodate fuel and the AF bought it later in the production run. It seriously effects the cargo box height and loading tall things like helos
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 3:23 pm

LCDFlight wrote:
If the fuselage tank catches fire, this could be deadly to passengers. However, a fire in a wing tank would also be quite hazardous, at least as I picture it.


Outcomes, in flight, would be much the same—fatal. You’d either burn up the fuselage or the wing would fail and loss of control crash.
 
mxaxai
Posts: 2811
Joined: Sat Jun 18, 2016 7:29 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 11:05 pm

High wing aircraft tend to not have fuel in the wingbox. The A400M has a center tank, though.

The explosion or sudden ignition of fuel contained in modern fuel tanks is virtually impossible. Fuel generally only becomes a fire hazard on the ground, where it can leak onto hot items like engines and brakes, or after a crash. Though wing tanks can be plenty dangerous as well, as evidenced by SU 1492.
 
Max Q
Posts: 9126
Joined: Wed May 09, 2001 12:40 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 11:26 pm

GalaxyFlyer wrote:
Max Q wrote:
GalaxyFlyer wrote:
The only large planes I can think without center fuel are the C-130, C-141 and C-5. The C-17 added fuel in the wing box as a cut-in during production—60,000#, I think. They needed the range. I don’t think the Gulfstreams have center fuel, either.



Isn’t that center fuel tank on the C17 clearly visible above the cabin ?


It is, I don’t know if the tank was adapted or the wing designed to accommodate fuel and the AF bought it later in the production run. It seriously effects the cargo box height and loading tall things like helos



It’s interesting to see that modification, I don’t think that sort of installation would ever be permitted in a civilian aircraft


You literally have a large fuel tank inside the pressure cabin above the heads of any passengers and crew members
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Wed Oct 27, 2021 11:55 pm

I’m not positive it’s in the pressure vessel, it might not be any different that a center wing box tank, just overhead. No, I’m not saying it isnt, either, I just don’t know. While there is more flexibility in military certification, the C-17 does have civil certification.
 
Max Q
Posts: 9126
Joined: Wed May 09, 2001 12:40 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Oct 28, 2021 2:36 am

GalaxyFlyer wrote:
I’m not positive it’s in the pressure vessel, it might not be any different that a center wing box tank, just overhead. No, I’m not saying it isnt, either, I just don’t know. While there is more flexibility in military certification, the C-17 does have civil certification.


Since it’s installation is clearly visible overhead the cargo hold there’s obviously nothing separating it from the pressure vessel so it must be inside it


You said yourself that it reduces the available space for loading larger items


I understand that more fuel that needed, all I’m saying is this would never be allowed in a civilian aircraft passenger cabin
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Oct 28, 2021 2:52 am

If the wing box is outside the pressure hull, it’d be just like any passenger liner. Or, like ACT tanks in baggage. I don’t know how it was designed, I do know the wing box reduces the ceiling height from friends who flew it, esp loads. Maybe ASD knows how it was certified, maybe it’s like the A400.
 
tommy1808
Posts: 14691
Joined: Thu Nov 21, 2013 3:24 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Oct 28, 2021 3:07 am

Tristarsteve wrote:
The Airbus has the option of "ACT"s, Additional Center Tanks, to enhance its range, available on the 319, 320, and 321, but I've only heard of it being installed on the A321


Qatar Airways has two A319 aircraft fitted with an ACT.
They have provisions for six ACT which would fill up both holds, but when I worked on them only one was used, at the front of the rear hold.
We used to send it from ARN to DOH and put fuel in the ACT often. The aircraft had a standard cabin with lie flattish seats in business class and the passenger bags filled the rest of the holds.
I assume the aircraft were bought as business jets? but used by the airline.


Aren't those just A319LR, the Airbus equivalent to the 737-700ER? I think AF had a small number too for those too long for a normal NB, to thin for a WB routes.

Best regards
Thomas
 
Max Q
Posts: 9126
Joined: Wed May 09, 2001 12:40 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Oct 28, 2021 4:01 am

GalaxyFlyer wrote:
If the wing box is outside the pressure hull, it’d be just like any passenger liner. Or, like ACT tanks in baggage. I don’t know how it was designed, I do know the wing box reduces the ceiling height from friends who flew it, esp loads. Maybe ASD knows how it was certified, maybe it’s like the A400.



Not talking about the wing box though , this fuel tank is exterior to that but inside the hold.


Obviously it was the only place there was room to install an additional tank
 
travelsonic
Posts: 163
Joined: Sat Apr 07, 2007 8:59 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Oct 28, 2021 4:14 am

convair880mfan wrote:
Thinking about what the others have written here made me think that if center fuel tanks were dangerous, the FAA and the aviation authorities of other countries would not allow them in commercial aircraft..


I wish I could be optimistic like that - but seeing how often changes seem to only come after tragedy (look, for instance, at Swissair 111 - the U.S govt banned metalized mylar AFTER the crash despite KNOWING how damn flammable that stuff was), IDK.
 
celestar345
Posts: 78
Joined: Wed May 08, 2013 5:35 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Fri Oct 29, 2021 11:23 am

Horstroad wrote:
The center wing tanks usually are the largest. On the 777 (-200LR/-F/-300ER) for example the center tank holds 184,480lb and the wing tanks 69,630lb each. I think some early versions of the 777 didn't use the space in the center wing box for fuel. The two compartments of the center tank in the wings were connected by a pipe.


It's the 777-200 non-ER versions. The dry bay still need to be inspected for SFAR88 during checks though...

Horstroad wrote:
Always think like that: If it was dangerous, it wouldn't have been certified.


Absolutely - and actually for 767/777, once you remove the floor panel about the wingbox it's the fuel tank. Quite a few times when I am doing the centre tank inspection I would knock on the tank ceiling and scream let me out to scare those who are working in the cabin...
 
celestar345
Posts: 78
Joined: Wed May 08, 2013 5:35 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Fri Oct 29, 2021 11:25 am

tommy1808 wrote:
Aren't those just A319LR, the Airbus equivalent to the 737-700ER? I think AF had a small number too for those too long for a normal NB, to thin for a WB routes.

Best regards
Thomas


Mostly ACJs, I worked on one before with 4 installed, 2 in front and 2 in the rear hold.
 
Dalmd88
Posts: 3209
Joined: Fri Jul 28, 2000 3:19 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Sun Oct 31, 2021 4:06 pm

The 727 also had an optional cargo hold tanks like the Airbus ACT system.

I recall some of our old Western 727 had the aft tank installed and the provision for a fwd cargo tank. The aft tank sat just fwd of the aft cargo door. Overhauls for those planes were a real pain. The tank had to be removed to inspect the interior belly section.

As others have mentioned the 727 also had the standard Center tank under the cabin. The DC9 and MD80 also had center tanks under the cabin. The 727 access for the center tank was on the bottom of the tank. Portions of the air condition packs had to be removed I think to get to it. For the DC9/MD80 there were two access holes from inside the cabin. Those had a special sealing system to keep vapors out of the cabin. Back in my overhaul working days I spent many nights in one of these tanks. Tank work was never fun.
 
Gr8Circle
Posts: 2648
Joined: Fri Dec 02, 2005 11:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Sun Oct 31, 2021 5:08 pm

Questions about the horizontal stabilizer tank: 1) on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU? ; 2) How do they fill the tail tank? Is it through the ports on the wings or is there a separate filling point?

Thanks for any responses to these questions :)
 
User avatar
fr8mech
Posts: 8392
Joined: Mon Sep 26, 2005 9:00 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Sun Oct 31, 2021 6:23 pm

Gr8Circle wrote:
Questions about the horizontal stabilizer tank: 1) on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU? ; 2) How do they fill the tail tank? Is it through the ports on the wings or is there a separate filling point?

Thanks for any responses to these questions :)


The tail tank will typically feed the center tank.

It is fueled the same way the other tanks are filled.
 
User avatar
Starlionblue
Posts: 20867
Joined: Fri Feb 27, 2004 9:54 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Sun Oct 31, 2021 11:44 pm

Gr8Circle wrote:
Questions about the horizontal stabilizer tank: 1) on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU? ; 2) How do they fill the tail tank? Is it through the ports on the wings or is there a separate filling point?

Thanks for any responses to these questions :)


On the A330 the trim tank is used to control in flight CG in order to increase efficiency. In general, the fuel is used to feed the engines. APU burn is normally very small compared to engine burn, so you wouldn't need a separate tank for it.

APU fuel feed is a bit complex.
- The APU is fed from the left inner tank on the ground after two minutes, and in flight above FL255 (if there is fuel in the trim tank).
- The APU is fed from the trim pipe during the first two minutes on the ground, during trim tank refueling and during aft fuel transfer.
- The APU is fed from the trim tank above FL255 (if there is fuel in the trim tank), and during forward fuel transfer.

The tail tank is filled through the trim pipe during normal refueling. There is no separate filling port. The fueling system automatically distributes fuel to the tanks dependent on the fuel filling target.

Sounds complicated? It is. One of my ground school instructors introduced the fuel system with the statement, "The fuel system on the A330 was obviously designed by a lunatic." To which I would add, "... for the purpose of giving examiners obscure details to ask during a line check..."
 
GalaxyFlyer
Posts: 8593
Joined: Fri Jan 01, 2016 4:44 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Nov 01, 2021 1:54 am

Starlionblue wrote:
Gr8Circle wrote:
Questions about the horizontal stabilizer tank: 1) on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU? ; 2) How do they fill the tail tank? Is it through the ports on the wings or is there a separate filling point?

Thanks for any responses to these questions :)


On the A330 the trim tank is used to control in flight CG in order to increase efficiency. In general, the fuel is used to feed the engines. APU burn is normally very small compared to engine burn, so you wouldn't need a separate tank for it.

APU fuel feed is a bit complex.
- The APU is fed from the left inner tank on the ground after two minutes, and in flight above FL255 (if there is fuel in the trim tank).
- The APU is fed from the trim pipe during the first two minutes on the ground, during trim tank refueling and during aft fuel transfer.
- The APU is fed from the trim tank above FL255 (if there is fuel in the trim tank), and during forward fuel transfer.

The tail tank is filled through the trim pipe during normal refueling. There is no separate filling port. The fueling system automatically distributes fuel to the tanks dependent on the fuel filling target.

Sounds complicated? It is. One of my ground school instructors introduced the fuel system with the statement, "The fuel system on the A330 was obviously designed by a lunatic." To which I would add, "... for the purpose of giving examiners obscure details to ask during a line check..."


He should have taught CL 604 fuel system—a drunk lunatic. No synoptic pages and 22 abnormals.
 
User avatar
Horstroad
Posts: 613
Joined: Thu Apr 08, 2010 8:19 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Nov 01, 2021 2:59 am

Gr8Circle wrote:
on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU?

The primary purpose of the tail tank on most aircraft is for CG control. Secondary would be additional fuel storage space.
On the MD-11 the APU shares the fuel feed line with the #2 engine. It has a dedicated bypass around the fuel fire shutoff valve so the APU can be used even with the ENG #2 fire handle pulled (and vice versa).
The tail tank can feed ENG #2 and the APU directly, but the primary fuel supply for the #2 engine and the APU is Tank #2


Gr8Circle wrote:
How do they fill the tail tank? Is it through the ports on the wings or is there a separate filling point?

On large aircraft no tank has dedicated fill ports. The aircraft usually has two fill ports on each wing. On Boeings one side is equipped with a control panel, Airbus put the control panel in the lower fuselage.
All refueling adapters connect to a manifold. This manifold is used to distribute fuel around the aircraft. Each tank has a fill valve and a transfer pump connected to that manifold. Also the fuel jettison system uses this manifold. On the MD-11 the tail tank has a dedicated transfer line that runs in parallel to the ENG #2 fuel feed line and connects to the fill/crossfeed manifold.

Here you can see a simplified schematic of the MD-11 fuel system. I color coded the fill/crossfeed manifold in magenta:

Image
 
Tristarsteve
Posts: 3706
Joined: Tue Nov 22, 2005 11:04 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Mon Nov 01, 2021 12:36 pm

The primary purpose of the tail tank on most aircraft is for CG control.


Except the B747-400, where the fuel only flows out, usually to the centre tank.
It is emptied very early in the flight, and if it fails to empty the aircraft must land soon before the C of G goes too far aft.
Refuelling can be a challenge. There are two models to fill it. Some airlines start at around 130 tons, and some wait till around 150 tons.
But then it must be split between the centre and tail tank in the correct ratio. All in the book, but if the crew change the fuel figure from say 127 tons, to 134 tons, you can be way out. You only do it once, then you stop and wait for the final figure.
 
celestar345
Posts: 78
Joined: Wed May 08, 2013 5:35 pm

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Nov 04, 2021 5:33 am

Gr8Circle wrote:
Questions about the horizontal stabilizer tank: 1) on planes that had/have the horizontal stabilizer tank, is that used primarily for feeding the APU?


The APU would feed off the tank which is used up last - say after landing the aircraft is parked overnight, and you want to be able to start up the APU the next morning without doing further work to transfer fuel to the tail tank.

Tristarsteve wrote:
Except the B747-400, where the fuel only flows out, usually to the centre tank.
It is emptied very early in the flight,


Oh the "single point sensor"....
Yes it feeds only to the centre tank, once the level drops below the sensor fuel transfer will happen automatically (if my memory serves me right).
 
User avatar
jetmech
Posts: 2391
Joined: Wed Mar 29, 2006 2:14 am

Re: Is it dangerous when aircraft carry fuel in a center tank beneath the passenger cabin?

Thu Nov 04, 2021 9:33 am

Tristarsteve wrote:
But then it must be split between the centre and tail tank in the correct ratio.

5.2 : 1 IIRC?

Regards, JetMech

Who is online

Users browsing this forum: Snuffaluffagus and 15 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos