Yes the 757/767 does takeoff with center fuel pumps on with some exceptions. Naturally the first one is if the fuel in the tanks is less than 1000 lbs you can't run them anyway. The fuel system will scavenge out that fuel. You must have at least 5,000 lbs in the center tank to run them on takeoff. If you have less than 5,000 you'll have less than 1,000 in the tanks before reaching 10,000 which is a distractor in that portion of flight. So what we do is leave them off and once we get to a less busy time we'll turn on the center pumps and burn down to 1,000.

captain87 - That's not the reason. The Fuel recirculation to IDGs is automatically inhibited during take off & climb. FCOM 1, 1.70.40, page 6.

flyr767 - Yes, agreed. The exception is for obvious reason that it does not alert the pilots unnecessary during high workload period and it is not for the reason of contamination.

The op wasn't about B75/76 but one of the reasons you can use centre tank fuel on these aircraft is that all the fuel pumps are operating all the time. The centre tank pumps operate at a higher pressure than the wing tank pumps and thus the aircraft uses centre tank fuel first. If the centre tank pumps fail, the wing tank pumps are already operating and can provide a continuas flow in a very high power and critical situation, without the engine being starved by low pressure. This is not the case in the A320. In this aircraft a low fuel pressure would have to be sensed before the aircraft would switch to wing tank fuel.

Nope, Jonty, that's not the case in A320. A320 center tank fuel operation logic is the same with Boeing aircrafts (737/757/767/777).

"All fuel pumps (wing pumps & center tank pumps) remain on throughtout the flight. They are fitted with pressure relief sequence valves which ensure that, when all pumps are running, the center tank pumps will deliver fuel preferentially"
FCOM 1.28.10, page 2.

Wing Tanks Pump PushButton - On
"Pump is on but fuel feeds only when center tank pumps delivery pressure drops below threshold"
FCOM 1.28.20 page 1.

Learn something new every day, thanks for that.

You are most welcome. It's all about learning and it is what this forum is for.

Very good discussion but just wonder, where's the Airbus Engineer?

My thought on this subject:

Obviously half of the sky (Boeing) does take off on center tank fuel.

To my knowledge this has never caused any accident.

But it is true that in theory there is a risk of contamination going to both engines at a critical time.

Flight Detent has explained very well why this does not apply to the 321.

I think the real reason is Airbus thinks they know better than Boeing, and must make everything better than its competitor.

That's the simple reason why, being their airplanes more sophisticated than Boeing (at least in their mind...), they excluded the remote possibility of this contamination problem with a prohibition of their own.

LEM

Perhaps they require two pumps feeding each engine for takeoff.

Not true!

The QOTS takes off using tank to engine. Once flaps 5 (iirc) achieved pre-departure, the crossfeed valves to the fuel gallery from the centre tank are automatically closed, the providing tank to engine for take off until a suitable period of time afterwards.

Once they are opened again,m the fuel feeds from the centre tank (and the stab tank feeds the ctr tank) until empty, at whihc point the inners feed all engines untl mains 1-4 are equal at which point it is tank to engine again (when at about 52 tonnes remaining).

Che, this point has already been discussed, as all pumps are pumping together, the pressure is not the issue.

Top Bunk, forgive my ignorance, but what is QOTS? 747 maybe ??

LEM

QOTS = Queen of rhe Skies = B747:ok:

Aikon the A320 Centre Tank pumps run for 2 mins after engine start and then, as Capt87 says, shut off till slats are retracted
Ref 1.28.10 CT Pumps Control logic diagram
regards

Aikon
A320 - Clarification - IDG cooling is continuous, the fuel return to tank is inhibited during takeoff and climb, when it does start there has to be room in the outer or inner wing tank. Hence the wing tank fuel is used until the 500 kg. underfull sensor operates, then the CTR pumps run again.
See FCOM 1.28.10 p.6

it says the fuel return valve is controlled by the fadec but doesn't specify that its inhibited during T/O and climb.

where can i find these facts.. :)

Hi guys,

I almost forgot about this until you guys brought it up again.

Anyway, this is the answer I got from Airbus. There's a requirement for certification that the engines are not fed by the same fuel tank. A321 meet this requirement because center tank fuel is transferred to the wing tanks first, then from wing tanks, fuel is supplied to both engines. But for A320, center tank pumps will have to be off until take off is completed to meet the requirement.

I do not know how Boeing managed to "circumvent" this requirement but probably like LEM said, Airbus always think they planes are better than Boeing thus their requirement are more stringent.

If so, all 737's (at least) are illegal.

So it can't be a legal requirement, I think just french perfectionism...


Btw, I'd be happy if they applied the same perfectionism to warm my feet on those lousy (when it comes to warming feet :mad:) cockpits!

LEM

LEM,

Like I said, I do not know how Boeing managed to circumvent the requirement.
It maybe just french "perfectionism", but those are the answers I got back from Airbus.

Yeah that's what they told me too...

Well, to be more precise, what my instructor told me...

A wannabee who thought none could take off on center tank.

When I told him that all 737's do that, he didn't know what to reply :ugh:

CTR tank feeding
 

Hello Mr. Aikon

CTR tank feeding during T/O is inhibited because our centre tank is equipped with two pumps and because of which only one pump supplies the fuel to its respective engine. In case of failure there is no backup for fuel feeding to that engine. And we are very well aware that T/O is a critical phase.