757 Flight Deck A/C Packs
 

Hello All,

Just a quickie - if you're on the ground with only the R pack running, where (apart from equip cooling) does the F/D air come from? All the diagrams indicate it comes straight form the L pack, and not from the mix manifold.

The only thing I was wondering is whether some of the mix manifold air is able to sneakily creep back up 'towards' the L pack (as there is no pressure in the duct) and then enter the F/D that way.

Many thanks in advance for the info.

NW3

During right pack only operation the air comes from the mix manifold. The air normally flowing into the mix manifold from the left pack reverses and comes out of the mix manifold and feeds the flight deck outlets.

Thanks vapilot.

Are there any valves etc. that operate to achieve this, or is it simply a case of air flowing freely?

NW3

When the left pack is on, the outlet pressure overrides any flow from the mix manifold, so no valves are required. Free airflow it is.