747 Classic H for landing

[Dutch74]

OK, ok. We all know why we want to set up the fuel panel on the 747 classic in the "classic H" configuration for takeoff, but I think we should keep it in the classic H config when tanks 2 & 3 are equal to 1 & 4 plus reserves. But my new company is adamant about closing the crossfeeds for 1 & 4 and just leaving #2 open to keep the manifold pressurized.

I would rather set it up with both 1 & 4 crossfeeds open (2 & 3 closed) to pressurize the manifold, but can't think of a good argument for it.

Any thoughts?

[callout]

If the crossfeed manifold develops a leak you would loose fuel from 1 and 4 tanks in the H. I know all xfeeds are open during xfer but after tank to engine No.2 should be the only one open.

[Flight Detent]

Only #2 open to pressurize the manifold,
Been that way for many years!

[screwdriver]

Perhaps you should approach this from another angle and ask yourself why we take off with both 1 and 4 open?

[Dutch74]

It's easy to understand why you have 1 & 4 open for takeoff and until 2 & 3 are equal to 1 & 4 plus reserves. But then we leave #2 open to pressurize the manifold??? Why??? Saying "it's been that way for years" doesn't explain anything. Why #2.

I know many carriers who don't use #2. Some use #1 and some use #1 & 4.

[Re-entry]

Boeing limitations allow flight with any one or #1 and #4 crossfeeds open.

Whatever floats your boat, I guess.

[SMOC]

My understanding is that number #2 is left open (from the 707 days) not to pressurise the manifold but so that it doesn't overpressurize. ie close all crossfeeds the very cold fuel is trapped in the manifold and heats up on descent, after landing expands and cracks the manifold.

Airbus discovered this not so long ago with fuel being trapped in the wing to stab manifold, so procedures were introduced to allow the fuel to expand into one of the tanks by leaving a valve open.

[Dutch74]

I agree with you about it being a carry over from the 707 days. But I can't see it preventing an overpressure of the manifold since the boost pumps (in the tank) pump fuel into the x-feed manifold. Not the other way around. Just my opinion.

[SMOC]

With a X-Feed open fuel is allowed to expand & contract at will, with pumps on or off but with them all closed it's basically trapped.

[screwdriver]

So Dutch 24, Why are 1 & 4 left open for T.O?

[Dutch74]

So... Is this a test? Or are you really curious?

[Dutch74]

Because 1 & 4 tanks are small tanks (only hold about 30,000lbs) and if 1 &/or #4 x-feeds fail closed you are truly going to have to maybe dump fuel and land since there is no way to get fuel to 1 & 4 engines without using the x-feeds. So you always takeoff with these valves open and leave them open until 2 & 3 are equal.

So whats your point?

[Dutch74]

One more thing

I forgot to mention. We leave 2 & 3 closed for takeoff due to the dihedral <SP> effect which causes 1 &/or 4 pumps to feed engines 2 & 3 as well as 1 & 4.