737 - Why is APU bleed connected to left pneumatic manifold

[mirkoni]

I just can not remember - but there must be a simple reason - why is that APU bleed is connected to left pneumatic manifold in Boeing 737?...

For the APU fuel feed I know it is connected to the left reservoir because there must always be some fuel in wing tanks (while center tank may be empty).

Thank you in advance
mirkoni

[Piper19]

Because the flight deck is connected to the left pack? The fuel could also be fed from the right wing tank, so I think it's more a design philosophy there.

[Dougie_diesel]

Just a theory..

Beacuse the HP ground connection is connected to the RH manifold?
(external services on A/C RHS)

[lief]

Boeing philosophy I would say...
Everything "important" on the 73 is often on the "left" side ! Easy to remember : it is a captain's plane

[RAT 5]

It's got to be connected to somewhere, and both is not necessary. Military thinking is left/right/left/right. Guess the lefts have it.

[mirkoni]

Ground connection to the right manifold could be.
Is it maybe about always starting first the engine no 1, which is connected to the left manifold? Do they necessarily always start No 1 first?

[RAT 5]

Do they necessarily always start No 1 first?

Not in any airline I've worked for.

[RVF750]

Don't read too much into it. There is an APU bleed elbow on one side and the other is the external connection. In the middle is a low pressure air connection. It has to go somewhere!

Tradional to start right to left starting away from the steps/ pax. So the external air is on the side that means you start in an unusual order- as it's an unusual event ( well, on NGs it is)... So logical the layout is as it is.

Drawn up in 1965 from existing parts, it's quite a historical design anyway.

[Capt Quentin McHale]

"there must be a simple reason"....... and there is


The APU bleed duct runs down the l/h side of the aircraft between the airframe skin and the rear cargo sidewall where there is plenty of room. Way too much redesign,weight gain etc involved to route the apu duct down the r/h side of the aircraft around/under/over the rear cargo door cutout. Hope this helps....


McHale.

[bigal cessna]

As a licensed engineer on the b737 ----------- ,it is to do with the electric distrubition of the electrical system of the aircraft when you start the engines -------with no apu available ----------------------------- if you start the right first , if i remember correct--- some instrument transfers units to the capt side dont kick in automatically ----------------------------- on some aircraft starting procedure can depend on which engines are fitted with hydraulic pumps say the bae 146 for example -------------------- on the b737 , the external air cart is connected to the right side , boeing designed that the left engine is always --- normally---- started first-----------if you have apu air ,you wont it to go to the left engine and not to the right engine by having the bleed air crossfeed closed ----------------------------------- i have had one time the external starting air connection flapper failed and to get that engine started , external air cart was connected for start , and after starting the no 2 engine bleed and the crossfeed valve closed and both on mel [ not sure if there were pax ]

[Wodrick]

"there must be a simple reason"....... and there is
It's a Boeing, they have always done it that way why change ?