Fuel Crossfeed

[Leave 5 on the glide]

Guys and girls - could someone tell me the reason behind not having the fuel crossfeed open for take-off or landing please (generic A/c type)?

Thanks very much,

l5otg

[Blinkz]

I have to admit that I'm also curious about this as well. The main reason I've always thought it is to try and keep the two engines fuel systems separate. E.g if one side of the system has contaminated fuel then the other side won't be affected. However this doesn't make a huge amount of sense since all the fuel will most likely have come from the same fuel truck.

[milodk]

Maybe it is because if you have a leak in the fuel feed system to one engine, you do not want to emty both fuel tanks in one leak.

wasn´t there a A330 that ran out of fuel because of that ?

MiloDK

[wileydog3]

I don't remember any machine in recent years where we took off or landed with the xfeed open. That includes the 707/720, 727, 737, 757, 767, MD-80, Airbus, Learjets, Citations, etc.

In the KC-135 we had the x-feed manifold pressurized with the valve open for number 2 but all the others were closed.

What airplane are you thinking of?

[Checkboard]

I remember years ago when practising engine failures in the sim, we would just pop open the cross-feed to make "one big tank", and keep flying with a nice symmetric fuel load.

When the manufacturer found out about it, they were aghast. The problem was that the simulated fuel pumps were all identical, producing identical outputs, and thus a matched fuel feed from each tank - so the procedure worked fine in the sim.

In the real world the manufacturing tolerance results in each pump having a slightly different output pressure. If you just open the cross-feed, then the side with the pumps providing the slightly higher pressure supply all of the fuel, overriding the output of the pumps on the other side - so you rapidly get a large fuel imbalance - and the side of the imbalance is unpredictable.

[Gooneyone]

So here's the question worded slightly differently: Could someone tell me why we should take-off with the crossfeed open?
I couldn't think of one.
P.S. No crossfeed on the Dash 8, only fuel transfer tank to tank.

[Pilot Pete]

milodk and checkboard have answered your question admirably!:ok:

PP

[SNS3Guppy]

That really depends on the aircraft. We are required to have at least one crossfeed open and the crossfeed manifold pressurized for takeoff and landing.

You really can't pose a question like this without specifying an airplane, because the reasons and the practices are going to vary with the specific fuel system, and in many cases, the type of fuel feed operation in progress (depending on the fuel load). We may be feeding from the crossfeed manifold via the jettison/fueling manifold from a center tank, we may be feeding directly tank to engine, and it all depends on the specific airplane and the fuel load we're carrying as to which of five fuel feed configurations we're using at any given time.

We have at least one crossfeed open all the time with fuel supply and pressure to the crossfeed manifold because in the event we do need to crossfeed, it's not the time to start trying to get fuel there. Putting fuel in there from an empty manifold would take about 20 seconds and about 600 lbs...rather than end up in a situation where we need the fuel and don't have it...we keep it full and pressurized all time.

In situations in which the center tank fuel will be used, it's fed through the jettison manifold to the crossfeed manifold, to the engines. In situations where the inboard tanks have more fuel than the outboards plus their reserve tanks, then the inboards are feeding themselves and the crossfeed maifold via the jettison manifold, and the outboards are feeding from them via the crossfeed manifold, etc.

Some systems have crossflow or crossfeed open all the time, some only when a crossfeed or balance operation is in progress. You'll have to be aircraft-specific, because it really depends on many factors, starting with the aircraft system, and ending with what one wants to do with it.

[BelArgUSA]

I leaned many things about planes in my aviation career. And often, I studied "rules and facts" that I found to be erroneous later with other airplanes. Fuel feed configuration is one of these subjects. Each airplane is "specific", there is NO GENERIC way to operate an airplane's fuel system.
xxx
I started my career with PanAm, first position was F/E on 727... Was my first "big plane"... The ground school instructors were good, we swallowed all they said as gospel from the bible. I remember them saying "you feed fuel from tank to engine for takeoff"... "on a Boeing, you cannot transfer fuel from one tank to another"... "you keep the crossfeed line pressurized"... "all boost pumps ON for takeoff and landing" were the many words highlighted in my manuals.
xxx
Then I had to learn the 707 and 720... was great... just many more tanks, lots of more fuel, and the basic rules studied for the 727 were applicable to the 707/720. Was almost like a difference course more than a new initial... And I honestly believed ALL PLANES were like that...
xxx
For the next 12 years or so, I got to fly the 707 and 727s... from F/E, then F/O, then captain... very little study to do, nothing new, except flying 707 or 727 airplanes coming from other airlines, and learning where the switches were. Different weights, different limitations, different red lines on EGT... "dash this" and "dash that" for engines...
xxx
Then flying on a contract with 707s as captain, the company had good and bad news for us 707s crews... "We lost the 707 contract" (oh oh! - is it a loss of a job, and furlough again) - No... it was not, we were going to be trained on DC-8s...
xxx
My next fear was - "Well, never flown a DC-8, so THEY will put me in the F/O seat for a few months"... and fears of a reduction in salary... Was not the case. I was going to check-out as captain immediately, despite no experience on DC-8 type.
xxx
So we went to ground school again. This time was United in Denver. Different manuals and procedures, different vocabulary for the Douglas machines. And completely different fuel system than Boeing. No sleeping in the classrooms. We had to study this Douglasosaurus. In a DC-8, we could transfer fuel from any tank to any tank, or to any engine. Sure, it was tank to engine for takeoff and engine (finally a similarity) but NO BOOST PUMPS ON for takeoff and landing... Had to highlight lots of differences...
xxx
So I flew a few years with the Diesel-8, going back occasionally on the 707 for other contracts... Then finally back to PanAm, on the 727... and the 747, the whale... What a delight to study the 747... was like a big and fat 707, with all the advanced systems of the 727... a delight to study... And the 747 turned out to be the easiest airplane to handle, of all the types I flew.
xxx
But the Boeing "rules" on the 747 were at times different. I learned that "tank to engine" did not apply for takeoff. Inboards were to be "tank to engine", while outboard engines were fed from the CWT... And that you could "transfer fuel from any tank to any tank" using the jettison system. Then it was "empty reserve tanks 2 and 3 after takeoff - keep reserve tanks 1 and 4 full until the end of cruise"...
xxx
NO GENERIC airplane to explain fuel systems. All planes are different.
In my F/E and F/O days, I flew the Learjet as type rating CFI to make extra money. Fuel management was quite a bit different with these machines as well, and many differences within the 20 series, 30 series, and the 55... They did not have "crossfeed" - they had "crossflow"... jet pumps... And worse, the maximum ZFW included the weight of any fuel in the fuselage tank. In a Learjet ZERO FUEL INCLUDES FUEL... sounds like Hebrew to me...
xxx
:8
Happy contrails

[BOAC]

L5otg - current UK company procedures on 737NG require x-feed closed for landing, but rumours abound of a change in Boeing procedures which has not yet reached 'us'. NB QRH for NG 'LOW FUEL' (<907kg/side ETOPS or <453kg/side) requires it open.

[ZAGORFLY]

here is my view:
in T/O phase you have surely enough fuel in each tank, therefore noo need to open a cross feed valve. why not keeping them segregated? Moreover the cross feed valve is there only for abnormal situations. What will happen if by playing open/close it remain struck open? If later you have a fuel leak situation you are in trouble. Therefore between the question close or open I vote close.
Then in the final approach phase why the need to have a cross feed valve open while in idle and in a phase more less like a glider.
open or close? irrelevant for me better not to touch it . and have one less call in the check list.

[SNS3Guppy]

in T/O phase you have surely enough fuel in each tank, therefore noo need to open a cross feed valve. why not keeping them segregated? Moreover the cross feed valve is there only for abnormal situations. What will happen if by playing open/close it remain struck open? If later you have a fuel leak situation you are in trouble.


Again, such generic commentary doesn't work, because the practices and procedures which are appropriate vary with the airplane, and the nature of the operation in progress at any given time.

Having crossfeeds open may be a very valid approach for the same reasons you've described...one doesn't want to risk it being stuck later, and for outboard tanks which hold a lesser quantity, having the crossfeed open and able to accept fuel from larger tanks for balance is a much better option than having it stay stuck closed and being unable to feed from other tanks.

What's opened when, and where, and how and why really depends on the airplane and what's being done with that airplane. Sometimes it's appropriate, sometimes not. One simply cannot make a generic statement about cross feed and have it be applicable on a general basis.

[Leave 5 on the glide]

Guys - thanks very much for the replies and info, much appreciated! :ok:

l5otg

[JAR]

CAA recommendation that if crossfeed is open during high power (take-off and go-around) and fuel pump breaks up then problems to more than one engine.

[RAM777]

bcz we MIGHT loose both the engines if the single pump that is being used wid the crossfeed on givesup....

[Deep and fast]

Emb 145

One pump can supply fuel for all phases of flight except take off and go around.

In this A/C you chose the tank that is low, the pump in the low tank switches off and the flow goes to both engines from the tank with the higher contents to balance the tanks.

D and F :8