Textbook Pneumatic – Pressurisation and Air

TEXTBOOK

PNEUMATIC – PRESSURISATION AND AIR CONDITIONING SYSTEMS

020 00 00 00 AIRCRAFT GENERAL KNOWLEDGE 021 06 00 00 PNEUMATIC – PRESSURISATION AND AIR CONDITIONING SYSTEMS

NO. 2 ENGINE

LP TO DEICING SYSTEM

AIR CONDITIONING

OFF OFF

RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN NORM 40 20 °C 60 0 DUCT TEMP 80

100 MIN MAX BLEED

CABIN

CAB F/C DUCT DUCT OFF

GAUGE F/C FAN

OFF AUTO MAN COOL WARMPACKS COOL WARM

TEMP F/A CABINCONTROL FLT COMP TO NO. 1 AIR- CONDITIONING PACK

TO NO. 2 AIR- FROM NO. 1 ENGINE CONDITIONING BLEED-AIR SYSTEM PACK (SIMILAR TO NO. 2 SYSTEM)

Pneumatic / Pressurisation / Air Conditioning

Table of Contents:

Air driven systems ______3 Pneumatic systems ______4 Air conditioning system ______14 Pressurisation ______25

Pneumatic / Pressurisation / Air Conditioning

Air driven systems

"Pneumatic, Vacuum systems" Pneumatic, or air driven systems, can be used to power gyroscopic flight instruments, provide pressurization and air conditioning, operate de-icing systems and power landing gear and brake systems in lieu of hydraulics.

Air Central Oil air filter seperator Heading indicator Oil

Attitude Engine Oil indicator

luprication Suction and cooling gage Turn and slip Vane-type Suction relief indicator vacuum pump valve Needle valve

F - 27 Pneumatic Landing Gear / Brake System

Sensing Line

L.H. Nacelle R.H. Nacelle Main Alternate Storage Bottle Storage Bottle

Isolating Valves

Isolating Valves ROD

Air Filter

Pneumatic Panel

Alternate Alternate Wheelbrake Landing Gear Nose Wheel Landing Gear Wheelbrake System Control System Steering Control System System

Pneumatic / Pressurisation / Air Conditioning

Pneumatic systems

"Gyro pneumatic systems" Venturi suction systems are simple systems, where a venturi tube mounted on the outside of the fuselage is directed into the slipstream of the propeller. Air flowing through the venturi produces a low pressure inside the instruments.

Propeller Wash

Venturi

Suction Pressure - reducing regulator needle valve

L R 030 N 330

L 2Min.Turn R

2 MIN TURN

Heading Attitude Turn und Slip indicator indicator indicator

Air flows into the instrument Air filter cases through built-in filters to Heading Indicator spin the gyros. The likelihood of ice buildup and venturi blockage during Attitude IFR conditions limits the use of Indicator venturi systems to light VFR Venturi suction aircraft. Turn and slip Indicator

Needle valve

Pneumatic / Pressurisation / Air Conditioning

Modern aircraft equipped with pneumatic gyros use engine driven vane type pumps.

Vane Type Air Pump

Inlet Outlet

Shaft

Vane

Case Rotor

Two types are in use - wet and dry pumps. Wet vacuum pumps are lubricated by engine oil. The oil lubricates and cools the pump, but has to be routed through an air-oil separator and drained back into the tank before the air can be directed overboard.

Air Central Oil air filter seperator Heading indicator Oil

Attitude Engine Oil indicator

luprication Suction adn cooling gage Turn and slip Vane-type Suction relief indicator vacuum pump valve Needle valve

Pneumatic / Pressurisation / Air Conditioning

Dry air pumps are lighter in weight and require no lubrication. They can drive gyroscopic instruments with the suction they produce, as seen in this schematic. Dry air pumps can also be used to produce positive air pressure. Pressure systems are necessary on aircraft which fly at high altitudes where there is not enough ambient air pressure to drive the gyros.

Twin Engine Vacuum System Vacuum Manifold check valve Vacuum regulator regulator

Air Suction Air Pump gage Pump

Attitude indicator Heading indicator

Dry Vane-type vacuum pump Rotor and vanes are made from carbon compounds. Filter Wear generates a microscopic carbon deposit which acts as lubricant

Twin Engine Pressure System

Inline Inline Pressure Pressure Manifold check valve regulator filter filter regulator

Inlet Inlet filter filter

Air Pump Air Pump

Gyro pressure gage Pilot´s gyros

Copilot´s gyros

Pneumatic / Pressurisation / Air Conditioning

“Bleed air" Turbine engine powered aircraft usually use bleed air from the engine compressor. This air is free from contamination and can be safely used for cabin pressurization and air conditioning.

Pneumatic / Pressurisation / Air Conditioning

Some aircraft use independent cabin compressors driven by bleed air to increase the volume of air taken into the cabin.

Flush air inlet Outside skin Compressor turbine Pressure vessel

Outflow valve Bleed air

Turboprop engine

Compressor

Another design uses a jet pump flow multiplier to increase the volume of air. The jet pump is essentially a venturi inside a line from the outside of the aircraft. A nozzle blows a stream of high-velocity compressor bleed air into the throat of the venturi which produces a low pressure that draws air in from the outside. This outside air is mixed with the compressor bleed air and carried into the aircraft cabin.

Flush air inlet Outside skin Pressure vessel

Jet pump Outflow valve Bleed air

Turboprop engine

Ambient Air

Compressor Bleed Air To Cabin

Pneumatic / Pressurisation / Air Conditioning

"APU bleed air" The Auxillary Power Unit installed on most larger airplanes is usually capable of providing bleed air to operate air cycle-machine-based air conditioning systems on the ground.

Some APU’s are designed to operate in flight and can, if required, provide bleed air for pressurization and airconditioning as a backup in emergencies.

ECS ECS PACK PACK LH RH

APU Pre-cooler Pressure regulator and relief valve Water seperator

AIRFOIL DEICING

Pneumatic / Pressurisation / Air Conditioning

"Ground Service Cart" To pre-condition the airplane on the ground predominantly diesel powered ground servicing carts can provide pre-heated or pre-cooled air at high volumes. Ground service connections on the outside of the fuselage allow the supplied air to be ducted into the aircraft air condition ducts.

BAGGAGE FLT COMPT CABIN COMPARTMENT

CABIN AIR FLT COMPT AIR

CONDENCER

MIXING BOX

COMPRESSOR

AIR CYCLE EXPANSION MACHINE (ACM) TURBINE Ground air service connector

Ground service connectors usually house a check valve to avoid loss of ship- supplied air once the cart is disconnected. To prevent the aircraft from becoming pressurized on ground at least one door should be left open if an air cart is connected and operating.

Air conditioning ground coupling

Pneumatic / Pressurisation / Air Conditioning

"Indications and warnings" As an example of bleed air related indication and warnings in a modern glass cockpit, look at the system of the Embraer 145. There are 5 types of indication for the air conditioning system.

- the indication on the engine indicating and crew alerting system display,

- the indication on the environmental page on the multi function display,

- the engine indicating and crew alerting system caution messages,

- the engine indicating and crew alerting system advisory massages and

- the central maintenance computer massages on the maintenance page of the captains multi function display.

155 FMS -38 SAT 88.2 CRZ 88.2 PACK 1 OVLD BSNB -12 TAT PACK 2 OVLD 3.5NM 88.2 88.2 PACK 1 OVHT 446 TAS PACK 2 OVHT 1 MIN RAM AIR VLV FAIL A A PACK 1 VLV FAIL PACK 2 VLV FAIL PACK 1 VLV CLSD 800 800 PACK 2 VLV CLSD N LUMEL BSNB 25 25 94.3 94.3 10 790KGH 790 KGH 1540KG 1540 KG

TGT UP UP UP TX ECSOXY BLEED 0 PRESS TEMP 81 81 81 81 CABIN TEMP +28 °C 4000 CKPT TEMP +28 °C 1800 PSI 7.4 100 1 ECS M/P OFF RTN T/0 A/I FUEL HYD ELEC RNG

MAINTENANCE MESSAGES 1/03

AIR COND 1 LEAKAGE 10/03 20:50 OCCUR:01 AIR COND 2 LEAKAGE 10/03 20:50 OCCUR:01 DIG TEMP CONTROL 1 FAIL 10/03 20:50 OCCUR:01 DIG TEMP CONTROL 2 FAIL 10/03 20:50 OCCUR:01 DUCT TEMP SENSOR 1 FAIL 10/03 20:50 OCCUR:01 DUCT TEMP SENSOR 2 FAIL 10/03 20:50 OCCUR:01

Pneumatic / Pressurisation / Air Conditioning

"Interface with other systems" Hot engine bleed air, mainly used for pressurization and air conditioning, can also be used for anti-ice and de-ice purposes such as engine intake and wing leading edge heating and de-ice boot inflation.

NO. 2 ENGINE

LP TO DEICING SYSTEM

AIR CONDITIONING

OFF OFF

RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN NORM 40 20 °C 60 0 DUCT TEMP 80

100 MIN MAX BLEED

CABIN

CAB F/C DUCT DUCT OFF

GAUGE F/C FAN

OFF AUTO MAN COOL WARMPACKS COOL WARM

TEMP F/A CABINCONTROL FLT COMP TO NO. 1 AIR- CONDITIONING PACK

TO NO. 2 AIR- FROM NO. 1 ENGINE CONDITIONING BLEED-AIR SYSTEM PACK (SIMILAR TO NO. 2 SYSTEM)

Pneumatic / Pressurisation / Air Conditioning

Bleed air is used to inflate door seals, power pneumatic autopilot servos and with the use of a venturi to generate suction, to control cabin outflow valves or drive pneumatic instrument gyros.

Inflatable ( pneumatic) door seal Quilted Fabric

1.00" Min Clearance

Door Seal

Side view of Quilted Fabric and Retainers Bleed air pressure reduced to 18 psi is used to inflate the door seal

Pneumatic / Pressurisation / Air Conditioning

Air conditioning system

"Conditioning the air in an airplane" used to just mean turning on the heat to warm the cockpit and cabin as airplanes generally fly in low temperature at high altitudes. Now with people accustomed to more creature comforts, cooling systems are used to make the cabins more comfortable when the aircraft is on the ground.

Airplane pressurization and air conditioning requires outside or "ambient" air to be forced into the aircraft cabin. The easiest way to achieve this is by using an air-scoop that extends into the slipstream. This ram air flow might be sufficient for low flying single or small multi- engine aircraft. Airplanes that cruise at altitudes of 10,000 ft or more require air supplied at a higher pressure to maintain an air pressure in the cabin which is comfortable and safe for crew and passengers. The source for this air depends largely on the type of propulsion used on a particular airplane.

22.000 ft 20.000 ft 18.000 ft Pressurization or 16.000 ft supplemental Oxygen required 14.000 ft 12.000 ft

10.000 ft

8000 ft 6000 ft Non pressurized 4000 ft 2000 ft Sea Level

Pneumatic / Pressurisation / Air Conditioning

"Cooling systems". Vapor cycle cooling systems use a compressor to pump a refrigerant through a closed system achieving a cooling effect once the gas expands into a heat exchanger - the so-called evaporator.

Vapor Cycle System Air cycle cooling systems are Heat exchanger - evaprator the true air conditioning systems since they are Cold air capable of controlling the air Re-ciculated cabin air Blower temperature over a wide range Inlet Outlet Thermostatic from maximum hot to expansion valve Compressor maximum cold depending on Receiver dryer the environment. Ambient air

Condenser

Hot exhaust air

AIRCOND / PNEUMATIC PAX CKPTRECIRC CABIN Environment control system pack

CH CH ATTND

PACK 1 PACK 2

XBLEED

WING 1 WING 2 START 1 GND START 2 CONN

BLEED 1 APU BLEED BLEED 2

LEAK LEAK

Ground connection

F a C T1 T2 Ovbd n T From engine T T To cabin Primary Heat T T Exchanger Water Emerg Collector Secondary Condenser ram Heat Exchanger Reheater

Ram air inelt

Pneumatic / Pressurisation / Air Conditioning

"Heating systems" Most small aircraft use one of two types of heating systems: The exhaust system heaters where air flows around the exhaust components and picks up heat before it is carried into the cabin.

Exhaust System Heater To cabin

Cabin heat From engine cylinders box Overboard

Ram air

Heater muff Exhaust overboard

Or combustion heaters that use fuel from the aircraft fuel tanks to operate an independent heater.

COMBUSTION HEATER

Combustion air scoop Sealed fuel control assembly Fuel Filter Fuel tank Pump

Combustion chamber Fuel filter Spray nozzle Heated air

Ignition unit Exhaust shroud Ventilating Exhaust air scoop Drain Drain Drain

Pneumatic / Pressurisation / Air Conditioning

"Sources of air supply" Airplane pressurization and air conditioning requires outside or "ambient" air to be forced into the aircraft cabin. The easiest way to achieve this is by using an air-scoop that extends into the slipstream. This ram air flow might be sufficient for low flying single or small multi-engine aircraft.

Air-scoop

Pneumatic / Pressurisation / Air Conditioning

Airplanes that cruise at altitudes of 10,000 ft or more require air supplied at a higher pressure to maintain an air pressure in the cabin which is comfortable and safe for crew and passengers. The source for this air depends largely on the type of propulsion used on a particular airplane.

AIR SUPPLY:

For airconditioning and pressurization

Turbo - Chargers

Blowers or Compressors

Gas -Turbine Bleed Air

"Air cycle machines" Gas turbine powered transport aircraft use compressor bleed air for pressurizing the cabins with temperature controlled air.

Pneumatic / Pressurisation / Air Conditioning

Our schematic shows the air conditioning system for a twin-engine jet transport aircraft with the engines mounted on the aft fuselage. This airplane has two independent air conditioning systems that supply the cabin with heated and cooled air that is mixed to produce pressurized air at the right temperature. Hot compressed bleed air is taken from the engines and from the auxiliary power unit. It passes through pressure regulating and shutoff valves, flow limiters and flow control valves to the air cycle machine where it is cooled. Some of the hot air is tapped off before it goes through the cooler and is mixed with the cold air by a temperature control valve to achieve the correct temperature. Gas turbine powered transport aircraft use compressor bleed air for pressurizing the cabins with temperature controlled air.

From R.H. engine Compressor Temperature Expansion turbine control valve 13th stage augmentation valve Air cycle machine Mix chamber Ground pneumatic Anti-icing connection Ground air pressure Primary heat conditioner regulating exchanger connection shutoff valve Cooling air selector valve Ram air APU load control Secondary heat Ground valve Manual exchanger cooling fan crossfeed Sonic venturi valve Flow conrol valve

Anti-ice thermostat Ram air valve Pressure regulating & shutoff valve 8th stage Water seperator Aft bleed check pressure bulkhead valve Water seperator temperature control valve From L.H. engine

Pneumatic / Pressurisation / Air Conditioning

"ACM cooling" The cold air for cooling the airplane is produced by removing heat energy from the hot compressor bleed air. The hot bleed air from the engines and APU flows into a primary heat exchanger where it gives up some of its heat to ram air that flows through ducts. After leaving the heat exchanger it flows through the air cycle machine where it is further compressed by the centifugal compressor. The temperature rise caused by this compression allows more heat energy to be removed as the air flows through the secondary heat exchanger. After leaving this heat exchanger the air gives up much of its energy as it spins the expansion turbine which drives the air-cycle machine compressor. Still more energy is extracted in the last stage of cooling as the air expands upon leaving the turbine. When it leaves the expansion turbine the air is cold.

Compressor

Expansion turbine

Air cycle machine

Cold air to temperature Primary heat control valve exchanger Cooling air Secondary heat selector valve Ram exchanger

Pneumatic / Pressurisation / Air Conditioning

"Flow control valves" Most flow control valves use butterfly valves to reduce or increase the flow of air in a duct.

High pressure shut off valve

Solenoid Actuator housing Electrical connector Actuator cover Access to filter

Butterfly Valve

Flow control valve

The position of the valve can be changed electrically through an electric motor or pneumatically, through a bleed air actuated piston and cylinder assembly. Flow rates can be a fixed setting for optimum performance of the air conditioning system or a variable setting allowing the crew to control the air flow within pre-set limits.

NO. 2 ENGINE

LP TO DEICING SYSTEM

AIR CONDITIONING

OFF OFF FROM CABIN RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN SUPPLY DUCT NORM 40 20 °C 60 0 DUCT TEMP 80

100 MIN MAX BLEED

CABIN

CAB F/C DUCT DUCT OFF

GAUGE F/C FAN

OFF AUTO MAN COOL WARMPACKS COOL WARM

TEMP F/A CABINCONTROL FLT COMP TO NO. 1 AIR- CONDITIONING PACK

FROM NO. 1 ENGINE TO NO. 2 BLEED-AIR SYSTEM AIR- (SIMILAR TO NO. 2 SYSTEM) CONDITIONING PACK

Pneumatic / Pressurisation / Air Conditioning

"Temperature control" Temperature is controlled within the air conditioning system by mixing hot engine bleed air with cold ACM discharge air. Electrically-operated butterfly valves control the amount of hot air added to the cold ACM discharge air.

Hot bleed air

Compressor Butterfly valve Expansion turbine

Air cycle machine

Cold ACM air Primary heat exchanger Cooling air

Pack bypass ACM butterfly valve butterfly valve

Pneumatic / Pressurisation / Air Conditioning

Dual valve systems can vary the ratio of airflow between the ACM and uncooled air. The result is a temperature-controlled air conditioning pack. Each pack consists of ACM, heat exchangers, ducting and control valves. Each pack feeds into a common mixing chamber from where ducts route the conditioned air into the cabin and cockpit air supplies. The temperature of individual ducts may be controlled by adding or restricting additional hot air using trim valves. Each pack consists of ACM, heat exchangers, ducting and control valves.

Pack 2 Air cycle machine FROM R.H. ENGINE COMPRESSOR TEMPERATURE Heat exchanger EXPANSION TURBINE CONTROL VALVE 13TH STAGE AUGMENTATION VALVE AIR CYCLE MACHINE MIX CHAMBER Ducting and GROUND PNEUMATIC control valves ANTI-ICING CONNECTION GROUND AIR PRESSURE PRIMARY HEAT CONDITIONER REGULATION EXCHANGER CONNECTION VALVE COOLING AIR SELECTOR VALVE RAM AIR APU LOAD MANUAL CONTROL VALVE SECONDARY HEAT GROUND CROSSFEED SONIC VENTURI EXCHANGER COOLING FAN VALVE FLOW CONTROL VALVE

ANTI-ICE Ducting and THERMOSTAT control valves PRESSURE REGULATION RAM AIR VALVE & SHUTOFF VALVE WATER SEPERATOR AFT PRESSURE 8TH STAGE BLEED BULKHEAD Heat exchanger CHECK VALVE WATER SEPERATOR TEMPERATURE CONTROL VALVE FROM L.H. ENGINE Pack 1 Air cycle machine

Temperature control panels are typically located in the cockpit with sub panels at flight attendant stations.

Cockpit

AIR CONDITIONING Flight attendant

OFF OFF

RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN NORM 40 CABIN TEMP LIGHTING NVS SYSTEM 20 °C 60 0 DUCT TEMP 80 CABIN PSU ON/OFF PAUSE 100 MIN MAX OVERHD TEST BLEED OFF PAUSE CABIN FAULT DEGRADED CAB F/C CABIN LAVATORY PSU SIDEWALL ON/OFF DUCT DUCT OFF

GAUGE F/C FAN

WARDROBEBUFFET AIRSTAIR OFF OVERHD DOOR AUTO MAN COOL WARMPACKS COOL WARM

TEMP F/A CABINCONTROL FLT COMP

Pneumatic / Pressurisation / Air Conditioning

"Humidity control" If a given amount of air is cooled the relative humidity increases in relation to the temperature decrease. In an air conditioning system this would lead to condensation in the packs and ducts. To reduce the humidity in the system condensers can be incorporated in the pack downstream of the heat exchangers.

RAM AIR

BAFFLE REFER TO TEMPERATURE CONTROL DESCRIPTION AND OPERATION TEMPERATURE PACK TEMPERATURE TRIM VALVES CONTROL VALVES

BLEED AIR RAM AIR DUCT TEMP OVERBOARD SENSING BULB SILENCERS

DUCT O TEMP DUCT TEMP SWITCH SENSOR

TO FLIGHT COMPARTMENT COMPRESSOR DISCHARGE CONDENSER OVERTEMPERATURE SWITCH MIXING HEAT BOX FILTER EXCHANGER

WATER RECIRCULATION TRAP

AIR FAN C T WATER NOZZLE RAM AIR SILENCER GROUND AIR SERVICE AIR CYCLE CONNECTOR MACHINE (ACM) (S.O.O. 8069)

Alternately water

separators may be PACK TURBINE WATER SEPARATOR BYPASS VALVE BYPASS VALVE installed as stand-alone

units downstream of the COMP PLENUM

ACM. FAN TURB CHECK BLEED AIR VALVE FROM No.1 AND No.2 NACELLES

RAM SCOOP EXHAUST LEFT WING REFRIGERATION PACK

Pneumatic / Pressurisation / Air Conditioning

Pressurisation

"Aircraft pressurization systems" High altitude is a hostile environment in which the human body cannot survive without a great deal of help. However, it is the ideal environment for long distance flight. Turbine engines operate efficiently and the lower density of the air decreases drag. The humidity at high altitudes is low, so weather conditions are excellent most of the time. Trial flights flown in the 1930's with pilots wearing pressurized suits proved the existence of strong high altitude winds today called jet streams. The first pressurized airplane flew in 1936. A special version of the Lockheed Model 10 Electra with turbocharged engines had a fully pressurized cabin and was able to make flights to an altitude of 25,000ft maintaining a cabin altitude of 10,000 ft or less.

Pneumatic / Pressurisation / Air Conditioning

"Principles of pressurization" Aircraft are pressurized by sealing off a strengthened portion of the fuselage called the pressure vessel and pumping air into it.

Baggage FLT COMPT Cabin compartment

CABIN AIR FLT COMPT AIR

Air conditioning pack

The cabin pressure is controlled by one or more outflow valves, usually located at the rear of the pressure vessel. The opening of these valves is controlled by the cabin pressure controller which regulates the amount of air allowed to leave the cabin in order to achieve and maintain a desired differential pressure or cabin altitude.

CABINE ALTITUDE DUMP 45 3 6 RATE 2 7 1 CAB ALT 8 M Outflow A INCR 0 9 N -1 1000 ft 10 valve AUTO

CAB NORM ALT BAR SET Control panel

Cabin pressure controller

Outflow valve

Pneumatic / Pressurisation / Air Conditioning

"Modes of pressurization" There are three modes of pressurization:

- the unpressurized mode,

- the isobaric mode and

- the constant differential mode.

"Unpressurized mode" In the unpressurized mode the cabin altitude is always the same as the flight altitude. The outflow valve remains fully open and the cabin pressure is the same as the ambient air pressure.

20000 CABIN 0 0 2 1 2 1 30 4 UP 6 2 20 6 0 DOWN 5 3 14 8 4 12 10 1 2

FT x FPM x 15000 DIFF PSI ALT 1000 RATE 1000

10000 tail section Cabin (unpressurized) (Pressure Vessel)

Outflow Valve 6000 fully open 5000 4000 3000 2000 1000 Sea level

Pneumatic / Pressurisation / Air Conditioning

"Isobaric mode" In the isobaric mode the cabin altitude always remains constant. The cabin pressure is maintained at a specific cabin altitude as the flight altitude changes. The cabin pressure controller begins to close the outflow valve at a selected cabin altitude. The outflow valve closes and opens or modulates to maintain the selected cabin altitude up to the flight altitude that produces the maximum differential pressure for which the aircraft structure is rated.

Isobaric Mode 20000 CABIN

0 0 2 1 2 1 30 4 UP Max Differential Pressure 6 2 20 6 0 5 14 8 DOWN 3 1 2 15000 4 12 10

FT x FPM x DIFF PSI ALT 1000 RATE 1000

10000 tail section (unpressurized) Cabin (Pressure Vessel)

Outflow Valve 6000 closed 5000 4000 3000 2000 1000 Sea level

Pneumatic / Pressurisation / Air Conditioning

"Constant-differential mode" In the constant-differential mode the cabin pressure is maintained a constant amount above that of the outside air pressure. Cabin pressurization puts the structure of an aircraft fuselage under a tensile stress as the pressure inside the pressure vessel tries to expand it. The cabin differential pressure expressed in "psid" is the difference between the internal and external air pressure and is a measure of the stress on the fuselage. When the cabin differential pressure reaches the maximum for which the aircraft structure is designed the cabin pressure controller automatically shifts to the constant-differential mode and allows the cabin altitude to increase, but maintains the maximum allowable pressure differential.

CABIN

0 0 2 1 2 1 30 20000 4 UP 6 2 20 6 0 DOWN 5 3 14 8 4 12 10 1 2

FT x FPM x Diff Pressure Constant DIFF PSI ALT 1000 RATE 1000

15000

10000

Diff Pressure Build Up

6000 5000 4000 3000 2000 1000 Sea level