Pneumatics, AC, Pressurization, Equipment Cooling

Question 1

Describe the Packs.

Answer 1

• Two identical packs cool bleed air from the engines, apu, or high pressure ground air.
• 2 identical pack controllers.
• Output is automatically increased during high demand (failed pack or recirculation fan).
• Increased output inhibited in some circumstances (SE/Aft Fire).

Question 2

Describe AUTO Mode.

Answer 2

The AC System automatically controls cabin temperature to a moderate, constant temperature by modulating pack output temperature.

Question 3

Describe the Bleed Air System layout.

Answer 3

• 4 Manifolds - L, R, C, Body - receive and automatically distribute bleed air from the engines or APU.
• L Side - Engine - (LP Valve, HPSOV(HI STAGE ovht sensor on -200s))(PRV)(ENG Anit-Ice Valve, TR(-300s)), OVHT Sensor (-300s), (L ENG BLEED VALVE), Starter, L HYD Reservoir, L Wing Anti-Ice, Center Manifold, (L ISLN Valve), Ground Pneumatic, L Pack.
• R Side - Same as Left, minus Ground Pneumatic
• C Manifold - Powered by Either engine or APU, Isolated by ISLN Valves and Backflow Valves FWD Cargo Heat
• Body Manifold - (APU)(APU BLEED VALVE), Bulk Cargo Heat, C HYD RES, AFT CARGO HEAT, ADP, C ISLN VALVE, Center Manifold

Question 4

What do the R and L ISLN VALVES isolate?

Answer 4

They Isolate their respective Pack and Wing anti-ice from the other side and center manifold.

Question 5

How do the Bleed Air Valves function?

Answer 5

• Electrically controlled, pneumatically activated.

Question 6

What does a VALVE light indicate?

Answer 6

• Disagreement.

Question 7

What does each Engine Bleed Valve control?

Answer 7

• Engine Bleed Valve.
• HPSOV.
• PRV.

Question 8

Describe an Engine Start from the Pneumatic perspective.

Answer 8

• Select GRND - VALVE Flash as Starter Valve opens.
• APU Duct Pressure increases above 21.
• Engine Bleed Valve closes, if open.
• Electrical System Sheds L Elec HYD Demand and Utility Bus (C2 HYD Already Shed, Center Fuel Pumps Inhibited)
• 50% N2, Starter Valve Closes, Ignition Stops, Onside C Fuel Pump Uninhibited, APU Valve Closes (Because of system logic - the engine is on and has priority).

Question 9

DUCT LEAK indication.

Answer 9

• No Automatic reconfiguration.
• QRH.
• You’ll isolate with the ISLN Valve and the Engine Bleed Valve.

Question 10

BLEED Light.

Answer 10

• Too much Bleed Air Pressure.
• Possibly due to PRV Malfunction or HPSOV Malfunction.
• No Aircraft Automatic Reconfiguration.

Question 11

OVHT Light

Answer 11

• Overheat.
• Engine Bleed Air Valve Automatically closes.
• You can reset once temperature reduces.

Question 12

What is indicated with four INOP Lights associated with the FLT DK, FWD, MID, AFT CAB Air Trim lights? One Light?

Answer 12

• You have the Trim Air Turned OFF.

- Associated TRIM AIR INOP due to selection or FAULT.

Question 13

What is the temperature range of the AC System?

Answer 13

18 - 30 Degrees C (24 is default)

Question 14

How do the controllers determine output temperature?

Answer 14

• They try to control the coldest section. We use TRIM Air to compensate.

Question 15

How do Recirculation Fans relate to Pack Operations?

Answer 15

• Recirc Fans increase Pack efficiency and decrease fuel consumption (.3% / pack) by reusing preconditioned air. When they are on, Packs will default to low flow., and when they fail, packs will increase flow.

Question 16

When will pack increase flow?

Answer 16

• Single Pack Operations
• Single Source (Except in flight, with an engine failed)
• Loss of a Recirculation Fan (Except with Aft / Cargo Fire).

Question 17

PACK OFF Light

Answer 17

• When Selected OFF.
• Pack Valve closed.
• No Bleed Air (Pneumatically actuated valves)

Question 18

Pack INOP Light

Answer 18

• Push to reset an overheated pack
• Illuminated due to overheated Pack.
• FAULT

Question 19

Cargo Heat

Answer 19

• aims for 4-10 Degrees C

- Two valves in each compartment - SOV and Heat Control Valve.

Question 20

Describe the Pressurization System.

Answer 20

• Automatically or manually controlled by adjusting discharge air through the outflow valve.
• Protected with positive and negative pressure release valves.

Question 21

Describe automatic pressurization modes.

Answer 21

• Control knob in AUTO 1 or 2 .
• If auto mode fails, control is automatically switched.
• Uses ADC Data, Selected Rate, takeoff altitude, and indicated landing altitude to schedule cabin pressurization.

Question 22

Describe Pressurization activity in relation to phase of flight.

Answer 22

• Takeoff - Starts with thrust application. Applies small positive pressure.
• Climb - Assuming Rate Selector is at the index, 500 fpm is the goal. If maximum differential, then pressurization is a function of climb rate and maintained at maximum differential pressure (8.6).
• Cruise - Landing Altitude and Scheduled Cabin PA are compared, and the Cabin pressurizes to the higher option. If a Cabin PA Climb is needed, it will be a half rate. Altitude changes of less than 1000’ do not trigger mode change.
• After 1000’ descent, A/C tries to descend at 300 fpm to reach slightly below QFE at touchdown. Bro correction from CA’s altimeter. At touchdown, outflow valve opens.

Question 23

CABIN ALT Discreet light
CABIN ALTITUDE Light
EICAS Message

Answer 23

Cabin PA > 10,000

Extinguish and reset when Cabin PA , 8500’

Question 24

AUTO INOP Light

Answer 24

• Both Automatic Controllers FAULT, or
• MAN Mode Selected.
• In Manual mode, The CLIMB/DESCEND knob controls outflow valve, and the relief doors are operated from the system.

Question 25

When will the outflow valve automatically close?

Answer 25

11000’ Cabin PA, in manual or automatic mode.