Flight Deck
Since the flight deck requires only a fraction of the air supply provided by the left pack,
most of the left pack air output is mixed with the right pack supply and routed to the
passenger cabin. Conditioned air for the flight deck branches into several risers which end
at the floor, ceiling, and foot level outlets. Air diffusers on the floor under each seat deliver
continuous air flow as long as the manifold is pressurized. Overhead diffusers are located
on the flight deck ceiling, above and aft of the No. 3 windows. Each of these outlets can be
opened or closed as desired by turning a slotted adjusting screw. There is also a dual
purpose valve behind the rudder pedals of each pilot. These valves provide air for warming
the pilots’ feet and for defogging the inside of the No. 1 windshields. Each valve is
controlled by knobs located on the Captain’s and First Officer’s panel, respectively.
Passenger Cabin
The passenger cabin air supply distribution system consists of the mix manifold, sidewall
risers, and an overhead distribution duct. Sidewall risers go up the right and left wall of the
passenger cabin to supply air to the overhead distribution duct. The overhead distribution
duct routes conditioned air to the passenger cabin. It extends from the forward to the aft
end of the ceiling along the airplane centerline and also supplies the sidewall diffusers.
Recirculation Fan
The recirculation fan system reduces the air conditioning system pack load and the engine
bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to
the forward cargo bay where it is filtered and recirculated to the mix manifold. The fan is
driven by an AC motor. The fan operates with the recirc fan switch in AUTO except with
both packs on and one or both in HIGH.
