747 Classic H for landing
Thread Starter
Join Date: Aug 2006
Location: Colorado
Age: 59
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
747 Classic H for landing
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?
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?
Join Date: Nov 2004
Location: thailand
Posts: 19
Likes: 0
Received 0 Likes
on
0 Posts
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.
Thread Starter
Join Date: Aug 2006
Location: Colorado
Age: 59
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
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.
I know many carriers who don't use #2. Some use #1 and some use #1 & 4.
Join Date: Jul 2000
Location: Smogsville
Posts: 1,424
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Thread Starter
Join Date: Aug 2006
Location: Colorado
Age: 59
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
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.
Thread Starter
Join Date: Aug 2006
Location: Colorado
Age: 59
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
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?
So whats your point?
Thread Starter
Join Date: Aug 2006
Location: Colorado
Age: 59
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
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.
Last edited by Dutch74; 8th Mar 2007 at 23:19.
