Air-con, pressurization

Question 1

Aircon general

Answer 1

Fully automatic system to provide cool air at specified temp - supplied by packs cooling warm air

2 packs supplied by hot air via 4 pack valves with inputs from:
Engines
APU
HP Ground air units

Each Pack (and associated pack valves) controlled via 1 Pack Controller - which has 2 independent channels

Cold air from packs mixed with recycled cabin/cockpit air (by the 4 Primary Fans) in Mixer Unit

9 Secondary fans recycle air from upper deck to upper/main decks

Question 2

Controllable zones (Aircon)

Answer 2

18 zones:
Cockpit
7 Upper deck
8 Lower deck
2 Cargo (BULK and FWD)
Crew rest compartment

To warm a zone, hot air added via Hot Air Valves and then 1 Trim Air valve per zone

Question 3

Cargo Aircon/vent

Answer 3

AFT cargo not aircon but is ventilated by BULK circuit

Air goes from Cabin though Inlet Isolation Valves into BULK and FWD CARGO compartments, and is then dumped overboard via extraction fans

Question 4

Bleed sources

Answer 4

Engines (Primary)
Normally from IP but also HP stages at low engine settings (controlled automatically bu HP valve)
Air goes through pre-coolers to cool air before it goes into bleed system
3 X-bleed valves isolate or interconnect the engine bleed systems

APU

Ground Air units

Question 5

APU bleed usage in flight

Answer 5

If <22,500’ and <M0.56, if the APU bleed valve opens and APU is supplying air, all engine bleed valves close)

Question 6

X-bleed rotary switch

Answer 6

Auto: all valves can operate independently

Open: All X-bleed and Engine bleed valves open

Close: All X-bleed and Engine bleed valves close, APU supplies ONLY Pack 1

Question 7

Outflow valves

Answer 7

4 (2 in forward and 2 in rear areas of the AC) control pressurization automatically during all flight phases

Each driven by single elec motor controlled by an outflow valve controller which operate in Auto, back-up or manual control modes. If both these fail, valve automatically closes

1 outflow valve can automatically control pressure in the whole AC

Question 8

Pressurization phases

Answer 8

Ground: all outflow valves open

TO: AC slightly over-pressurized for smooth transition

Climb: Press function of flight profile (max cabin V/S 1000 fpm) if in NAV but function of AC alt if in heading

Cruise: Max cabin alt 7500’ (Delta P approx 8 psi)

Descent: Function of flight profile - plans to pressurize to alt slightly lower than destination alt - max 300 fpm

After landing: all outflow valves open

Question 9

Negative relief valves

Answer 9

2 at aft bulkhead prevent excessive -ve diff press