sds1230-21-31-00

PRESSURIZATION CONTROL SYSTEM

AIRCRAFTMAINTENANCE MANUAL

EFFECTIVITY: 21-31-00

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PRESSURIZATION CONTROL SYSTEM

INTRODUCTION

The Cabin Pressure Control System (CPCS) controls cabin altitude,cabin rate of change and cabin differential pressure during all flightphases.

DESCRIPTION

The CPCS has two modes of operation: automatic and manual mode.The automatic mode is the primary mode. The manual mode is usedin case of failure of the automatic mode. The pressurization controlsystem has these components:

− Digital controller.

− Manual controller.

− Electropneumatic outflow valve.

− Pneumatic outflow valve.

− Pressure regulator valve.

− Check valve.

− Ejector pump.

− Static port.

− Air filter.

− Vacuum line.

− Reference pressure line.

The figure ″PRESSURIZATION CONTROL SYSTEM - MAINCOMPONENT LOCATIONS″ shows the location of the maincomponents of the system.


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DET. B

DET. D

AZONE

191

B

ZONES275276

DET. A

CD

ZONES223224

DIGITALCONTROLLER

MANUALCONTROLLER

PRESSURE LINE

VACUUM LINE

DET. C

PNEUMATICOUTFLOW VALVE

ELECTROPNEUMATICOUTFLOW VALVE

REFERENCE PRESSURE TUBE

VACUUM TUBE

STATICPORT

PRESSUREREGULATOR VALVE

PRESSUREREGULATOR VALVE

TUBE

VACUUM PUMP OUTLET

E

DET.E(LH SIDE)

CHECKVALVE

145AMM210188.MCE E

PRESSURIZATION CONTROL SYSTEM - MAIN COMPONENT LOCATIONS



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COMPONENTS

DIGITAL CONTROLLER

The digital controller is the unit which controls the cabin pressure rateof change. It has two basic assemblies, as follows:

− Mechanical sub-assembly.

− Electronic sub-assembly.

The digital controller does these functions:

− Keep the cabin rate of change as low as possible as the aircraftflight level changes.

− Automatic pre-pressurization sequence on the ground to preventcabin ″bump″ during takeoff.

− Takeoff without pressurization.

− Automatic depressurization sequence after landing to prevent cabin″bump″ during landing.

− Selection of the climbing rate to ″MIN″, to keep the pressurizationrate of change to a limit.

− Automatic in flight failure detection and automatic power up test.

− Selection of MAN mode.

The digital controller receives three parameters from the Air DataComputers (ADC 1 and ADC 2).

− Aircraft altitude (ZA).

− Aircraft rate of change (VZA).

− Barometric corrections (BARO).

The figure ″PRESSURIZATION CONTROL SYSTEM - DIGITALCONTROLLER″, and ″DIGITAL CONTROLLER″ table shows thecontrols and indications of the digital controller front panel.

DIGITAL CONTROLLER TABLE

REF.CONTROL/INDICATOR

POSITION/INDICATION

FUNCTION

1 DUMP Switch

Released

Turns off the fast depressurization mode.

The DUMP indicator in the switch stays

off.

Pushed

Select the fast depressurization mode.

The DUMP indicator in the switch turns

on.

2LAND ELEV

Display-

Shows the selected landing field eleva-

tion and fault indications.

3ELV SET

Switch-

Increases or decreases the landing field

elevation in the display. The increments

are of 100 ft at a speed of 200 ft/min.

The speed increases to 1,000 ft/min

after 5 seconds.

4AUTO/MAN

Switch

Released

Selects the automatic mode of operation.

The MAN indicator in the switch stays

off.

Pushed

Selects the manual mode of operation.

The MAN indicator in the switch turns

on.



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AUTO PRESSLAND ELEV (ft) ELV SET

+

-

DUMP AUTO/MAN

ON MAN

A

DET. A

1

2

3

4

145AMM210093.MCE C

PRESSURIZATION CONTROL SYSTEM - DIGITAL CONTROLLER



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MANUAL CONTROLLER

The manual controller is installed in the cockpit center console. In themanual mode, the manual controller operates the Pneumatic OutflowValve (POV) through its control knob. The control knob permits thecrew to set any cabin altitude rate of change between −1,500 and2,500 ft/min.

To get the necessary cabin altitude rate of change the crew must turnthe knob. The control knob turns a needle in the manual controller,which operates as follows:

− Turning the knob clockwise will connect the reference pressure lineto suction. This will make the cabin climb by opening the POV.

− Turning the knob counterclockwise will connect the reference pres-sure line to cabin pressure. This will make the cabin descend byclosing the POV.

NOTE: The reference pressure line has a capillary to cause apressure drop in the line to the pneumatic relay of thePOV.

The figure ″PRESSURIZATION CONTROL SYSTEM - MANUALCONTROLLER″ shows the unit.



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DNU

P

DET. A

DET. B

A

B

VIEW FROM PLATE

GREEN MARK(DN POSITION)VZ: -1500 ft/minAPPROX.

UP POSITIONVZ: +1500 ft/minAPPROX.

UP EXTREME POSITIONVZ: +2500 ft/minAPPROX.

WHITE MARK"LEVEL FLIGHT" ZONEVZ: 0

REGULATOR SHOWN IN"CABIN DESCENT" POSITION.VZ BETWEEN 0 AND -1500 ft/min

AUTO PRESSLAND ELEV (ft) ELV SET

+

-

DN

UPDUMP AUTO/MAN

ON MAN

145AMM210158.MCE A

PRESSURIZATION CONTROL SYSTEM - MANUAL CONTROLLER



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ELECTROPNEUMATIC OUTFLOW VALVE (EOV)

The Electropneumatic Outflow Valve (EOV) is installed in the rearpressure bulkhead through a flange/clamp connection. The body ofthe EOV is made of composite material.

In the automatic mode, the digital controller operates the EOV throughthe voltage supplied to the torque motor. In this mode, the EOVcontrols the Pneumatic Outflow Valve (POV) through the interconnect-ing tube. In the manual mode, the EOV stays closed.

The torque motor of the EOV has two nozzles: one is connected tothe cabin pressure reference line and the other to the suction line.The position of the torque motor quadrant (as a function of torquemotor input voltage) will open or close the nozzles.

The two nozzles connect to the servo-chamber of the EOV. At thelower part of the EOV, there is a compensation chamber connected tocabin pressure. When the pressure in the servo-chamber is the sameas the pressure in the compensation chamber, the EOV stays closed.This is a function of the spring in the servo-chamber.

The EOV has three safety devices, as follows:

− Overpressure relief valve.

− Negative pressure relief valve.

− Cabin altitude limiter.

The overpressure relief valve and the negative pressure relief valveare part of the same assembly. This assembly also has the connec-tion for the interconnecting tube, which connects the EOV to the POV.The overpressure relief valve has a manometric capsule which feelsthe cabin differential pressure. The inner part of the capsule feels thecabin pressure. The outer part of the capsule feels static pressurethrough the static port. When there is an overpressure, the expandedcapsule opens its valve. This will cause the EOV to open by decreas-ing its servo-chamber pressure.

When the outer static pressure is more than cabin pressure, it pushes

the EOV deflector. This causes the negative pressure relief valve toopen, decreasing the servo-chamber pressure and opening the valve.

The cabin altitude limiter has an aneroid capsule which feels cabinpressure. When cabin altitude is 14,000 ± 500 ft, the expandedcapsule opens its valve. This will close the EOV and keep the cabinaltitude to the limits.

PNEUMATIC OUTFLOW VALVE (POV)

The Pneumatic Outflow Valve (POV) is installed on the rear pressurebulkhead, through a flange/clamp connection. The body of the POV ismade of composite material.

The POV controls the cabin airflow outlet through the manual regula-tor when the system operates in manual mode. In the automaticmode, the EOV controls the POV through the interconnecting tube.

The POV has two safety devices: an overpressure relief valve and anegative pressure relief valve. These devices operate the same asthose in the EOV.

The figure ″PRESSURIZATION CONTROL SYSTEM - VALVEDETAILS″ shows the interior of the pneumatic and electropneumaticoutflow valves.



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DET. AACCESS PANEL272 DR

DET. CDET. B

C

B

POPPET SEAT

VALVE SEAT


POPPET SEAT

VALVE SEAT

PNEUMATICOUTFLOW VALVE

A

AIR FILTER

145AMM210169.MCE A

PRESSURIZATION CONTROL SYSTEM - VALVE DETAILS



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PRESSURE REGULATOR VALVE

The pressure regulator valve adjusts bleed air pressure from thepneumatic system (Ref. 36-00) to 20 ± 1 psig to supply the ejectorpump. This valve is installed forward of the wing-to-fuselage attach-ment. There is one valve on each side of the forward part of thewing-to-fuselage fairing.

CHECK VALVE

The check valve permits ejector pump operation in case one bleed airduct fails or no bleed air is supplied to one main bleed duct. Thisvalve is installed forward of the wing-to-fuselage attachment. There isone valve on each side of the forward part of the wing-to-fuselagefairing.

EJECTOR PUMP

The ejector pump makes suction using bleed air pressure through anair ejector. The pump receives an adjusted pressure of 20 psig at itsinlet.

This permits the pump to supply −3 psig on the suction line. Thebleed air flows overboard at the pump outlet.

The ejector pump is installed at the forward part of the wing-to-fuselage fairing.

The figure ″PRESSURIZATION CONTROL SYSTEM - PRESSUREREGULATOR, CHECK VALVE AND EJECTOR PUMP″ shows thelocation of the units.

AIRCRAFTMAINTENANCEMANUAL


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ZONE191

VACUUM LINE

EJECTORPUMP

PRESSUREREGULATOR

VALVE

PRESSUREREGULATOR

VALVE

PRESSUREREGULATOR

VALVE

REGULATEDPRESSURE(20 PSID)

EJECTOR PUMP

SUCTION(-3.0 PSIG)

DISCHARGEPORT

DET. A

DET. B

A

BB

C

DET. C

DET.D(LH SIDE)

CHECKVALVE

D

145AMM210162.MCE C

PRESSURIZATION CONTROL SYSTEM - PRESSURE REGULATOR, CHECK VALVE AND EJECTOR PUMP



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STATIC PORT

The static port feels the ambient static pressure through the sensingorifices. The static port transmits this signal to the related outflowvalve through a tube. This permits the overpressure relief valve tooperate.

The static port is electrically heated to prevent blockage of the sens-ing orifices because of freezing.

The static ports are installed at the lower part of rear fuselage I, nearthe cargo door.

AIR FILTER

The cabin air filter prevents nicotine and dust from going into theoutflow valves. This increases their life and reliability. The filter has afolded paper in a rubber housing with a threaded end.

The cabin air flows through the filtering element and goes to the EOVthrough the tubing at the threaded end. The air filter is installed nearthe EOV.

The figure ″PRESSURIZATION CONTROL SYSTEM - COMPONENTDETAILS″ shows the installation of some components of the system.



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A


PNEUMATICOUTFLOW

VALVE

PRESSURIZATIONSTATIC PORT


AIR FILTER

SEALANT


SENSINGORIFICES

DET. A

145AMM210163.MCE A

PRESSURIZATION CONTROL SYSTEM - COMPONENT DETAILS



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OPERATION

The pressurization control system adjusts the cabin pressure bycontrolling the exhaust rate of the cabin air from the EnvironmentalControl System (ECS). The system can operate in two modes:

− Automatic mode.

− Manual mode.

AUTOMATIC MODE

In the automatic mode, the Digital Controller (DC) operates the twooutflow valves (EOV and POV). The DC sends current signals to thetorque motor of the EOV to operate the two valves.

When DC Bus 1 is energized, it supplies the DC through the PRESSCONTROL circuit breaker. If the AUTO/MAN switch is released, theDC will start sending signals to the torque motor of the EOV tooperate the two outflow valves. The DC will then control the cabinaltitude (ZC) and the cabin rate of change (VZC). To do this functionthe DC receives these parameters:

− Cabin pressure, through its own pressure sensor.

− Aircraft altitude and baro correction, through signals from ADC 1and 2.

The DC program causes the measured cabin altitude (ZC) to be thesame or tending to a scheduled cabin altitude (ZCOT). For the ZCOT,the DC gives the correcting cabin altitude (ZCO). The ZCO is thevalue at which the system must adjust the ZC. The ZCO follows theZCOT up the cabin rate limit of change (VZLIM).

The DC will then supply the torque motor voltage to get the correctopening of the EOV. This will cancel the error between the measuredcabin altitude (ZC) and the calculated correcting altitude (ZCO). ThePOV will follow the movements of the EOV.

NOTE: The scheduled cabin altitude (ZCOT) can have differentvalues for different flight sequences, as follows:

– Automatic pre-pressurization sequence on the ground.

– Takeoff sequence (abort capability).

– Flight sequences (climb or descent).

– Automatic rate of descent increase sequence.

– Automatic depressurization on the ground.

The figure ″PRESSURIZATION CONTROL SYSTEM - SCHEMATICDIAGRAM″ shows the electrical interfaces of the system.



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CB0031

5

2

1

M

DC BUS 1

XK0264

A1

A3A2

X2

X1

K0264

AIR

GND

S0025

C3 NC3

NO3

50R

DC

WT0003

ENG 1 THRUST

LEVER SW

P0079

A

B

OUT FLOW VALVEREAR BULKHEAD

ENRGZ WHEN AIRCRAFTON GROUND POSITION

XK0412

A1

A3A2

B1

B3B2

X1

X2

K0412

AIR GROUNDPOSITION RELAY

ENG 1 THRUSTLEVER RELAY

DAU 1

225DTC-CKT BKR PANEL

J1019

A-30

A-65

P0078

L

K

H

G

V

T

J

A

U

C#

N

P

R

B

C

DC

28VDC PWR AUTO

DUMP POWER

LANDING GEAR INPUT

28VDC GROUND

CHASSIS

PIN PROGRAM

THROT INPUT

5 VDC GROUND

FAULT SIGNAL

FAULT SIGNAL INHB

A B

ARINC 429

( ADC 1 )

A B

ARINC 429

( ADC 2 )

+ -

TORQUE

MOTOR

OUTPUT

AUTO PRESN CONTROL

AUTO PRESN TEST

COCKPIT FLOOR

DC

J1

SH

C

224ERW-RIGHT RELAY SUPPORT

DIGITAL PRESSURIZATION CONTROLLER PEDESTAL

< 65

> 65

M

223IZ - ENGINE CONTROL QUADRANT

FV0003-275

SH

(30-41-50)-123

31-51-50

34-15-81

34-15-82

SH

PRESS

CONTROL

32-61-50

27-53-52

E

D

5 VDC LIGHTING

33-12-52

33-12-53

5 VDC PUSH-BUTTON

LIGHTING

FERRITE COIL

BONDING JUMPER

1

2

2

2

1

1

2

PRE-MOD. S.B. 145-21-0026

POST-MOD. S.B. 145-21-0026

145AMM210271.MCE B

PRESSURIZATION CONTROL SYSTEM - SCHEMATIC DIAGRAM



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AUTOMATIC PRE-PRESSURIZATION SEQUENCE ON THE

GROUND

When the aircraft is on the ground and the Thrust Lever Angle (TLA)is more than 65o, the pre-pressurization sequence starts. Thissequence prevents cabin ″bumps″ because of irregular airflow on thefuselage during rotation and takeoff. It also makes it unnecessary tocontrol cabin altitude immediately after rotation, as the cabin altitudefollows the aircraft altitude.

During this sequence the scheduled cabin altitude (ZCOT) is suchthat its scheduled cabin pressure (PCOT) is PCM + 15 mbar (to thescheduled altitude, ambient measured pressure at the ″full power″setting plus 15 mbar). The limit of cabin rate of change will be −450ft/min.

NOTE: For takeoff without air conditioning supply, this sequencecauses the outflow valves to close.

TAKEOFF SEQUENCE

As soon as the air/ground signal changes to flight condition, thetakeoff sequence starts.

This sequence prevents the re-selection of landing altitude if anaborted flight and emergency return to the takeoff field is necessary.

During this sequence, the scheduled cabin altitude (ZCOT) stays thesame as the ZCOT of the pre-pressurization sequence for 15 minutes.Or until the ZCOT is more than the theoretical cabin altitude, if itoccurs first.

NOTE: Theoretical law.

The theoretical cabin altitude is related to the aircraft altitude (ZA) andthe maximum climb performance of the aircraft (ZA = ZA.t). It is alsorelated to the maximum nominal differential pressure (7.8 psi) for acabin altitude of 8,000 ft at an aircraft altitude of 37,000 ft.

The function of the theoretical cabin altitude law is to have themaximum differential pressure at the lowest possible aircraft altitudewith a minimum rate of climb limit (maximum rate of cabin climb is600 ft/min for aircraft with CPCS digital controller of the P/N22250Nxxxxxx series and 700 ft/min for aircraft with CPCS digitalcontroller of the P/N 92185A010100).

The ″THEORETICAL LAW″ table gives the ZCTH.

THEORETICAL LAW TABLE

ZA ZCTH

0 to 5,000 ft 0.185359 * ZA - 1,500

5,000 to 10,000 ft 0.181550 * ZA - 1,481

10,000 to 15,000 ft 0.192977 * ZA - 1,595.2

15,000 to 19,000 ft 0.222177 * ZA - 2,033.2

19,000 to 24,000 ft 0.255186 * ZA - 2,660.4

24,000 to 29,000 ft 0.313587 * ZA - 4,062

29,000 to 33,970 ft 0.365719 * ZA - 5,573.9

above 33,970 ft 0.379658 * ZA - 6,047.3

The figure ″PRESSURIZATION CONTROL SYSTEM - PRE-PRESSURIZATION AND T/O SEQUENCES″ shows the graphicrelated to these sequences.



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FULLPOWER

TAKEOFF

AIRPLA

NE ALT

ITUDE

AIRPLANECLIMB

CABIN CLIMB

TIME

ALT

ITU

DE

0.2 psi

THEORETICALCABIN ALTITUDE

OVERPRESSUREDURING TAKEOFF

(BUMP)

15 min max.

145AMM210122.MCE A

- 450 ft /min

PRESSURIZATION CONTROL SYSTEM - PRE-PRESSURIZATION AND T/O SEQUENCES



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FLIGHT SEQUENCE

When the landing gear switch is in flight condition (but not during thetakeoff sequence) the flight sequence starts. During this sequencethe scheduled cabin altitude (ZCOT) is the higher value betweenZCTH and ZATT (landing altitude minus 300 ft, with barometric cor-rection from the ADC).

The cabin altitude rate of change limit (VZLIM) during this sequenceis:

− VZLIMCClimb = 600 ft/min for aircraft with CPCS digital controller of theP/N 22250Nxxxxxx series and 700 ft/min for aircraft with CPCSdigital controller of the P/N 92185A010100.

− VZLIMDDescent = −450 ft/min.

AUTOMATIC RATE OF DESCENT INCREASE SEQUENCE

When the aircraft rate of descent is more than −200 ft/min, thissequence starts. The function of this sequence is to calibrate thecabin rate of descent in relation to the aircraft descent profile.

In case of aircraft rapid descent, this sequence will increase the rateof descent limit (VZLIMD) in relation to the Remaining Flight Time(RFT). The RFT is calculated as follows:

− RFT = (ZA − (ZATT + 300))/VZA

The limit of VZLIMD is −500 ft/min.

AUTOMATIC DEPRESSURIZATION SEQUENCE ON THE GROUND

When the air/ground system is on the ground condition and the thrustlever is in idle, the automatic depressurization sequence starts. Thissequence prevents a cabin ″bump″ during landing.

To prevent the ″bump″ the cabin must have a small differential pres-sure. Thus, the automatic mode always controls the cabin altitude at

landing elevation selection minus 300 ft.

The automatic depressurization sequence on the ground cancels thisdifferential pressure of 300 ft. It also decreases cabin ″bump″ whenthe door is closed with the air-conditioning system on. The limit ofcabin rate of change (VZLIM) during the depressurization is 650ft/min.

When the aircraft is on the ground and bleed air is available, theoutflow valves go to the full open position when the system is turnedon.

The figure ″PRESSURIZATION CONTROL SYSTEM - DEPRES-SURIZATION SEQUENCE ON THE GROUND″ shows the graphrelated to this sequence.



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AIRPLANEDESCENT

AIR

PLA

NE

ALTITU

DE

AIRPLANE TOUCHDOWN

IDLE POSITION

CABIN ALTITUDE

OVERPRESSUREDURING LANDING

(BUMP)

-300 ft

+650 ft/min

OUTFLOW VALVESFULLY OPEN

p

AIR CONDITIONING OFFOR

MAIN DOOR OPEN

TIME

ALT

ITU

DE

AND THRUST LEVER AT

145AMM210121.MCE A

PRESSURIZATION CONTROL SYSTEM - DEPRESSURIZATION SEQUENCE ON THE GROUND



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MANUAL MODE

The manual mode pneumatically controls the cabin pressure. Theposition of the manual controller sets a reference pressure whichcontrols the opening of the Pneumatic Outflow Valve (POV).

The crew must turn the manual controller knob to get the necessarycabin rate of change. While turning the knob, the crew must follow theparameters on the EICAS display (Ref. 21-32).

During the manual mode, the digital controller is deenergized, and theEOV stays closed. The AUTO/MAN switch stays pressed and theMAN indicator in the switch stays on.

FAST CABIN DEPRESSURIZATION

When the NORM/DUMP switch, on the digital controller, is set toDUMP:

− It cuts the electrical connection between the digital controller andthe Electropneumatic Outflow Valve (EOV).

− It applies 10 V DC across the torque motor terminals. The torquemotor quadrant closes the cabin pressure port and opens thesuction port. The servo-chamber pressure decreases and the EOVopens.

− The DUMP indicator in the switch stays on.

NOTE: In flight, the cabin altitude limiter in the EOV will keep thecabin altitude to the limit of 14,000 ± 500 ft.

When the system is in the manual mode, turning the manual control-ler fully clockwise will also set a fast depressurization. The pneumaticoutflow valve will open and the cabin rate of climb limit will be of 2,500ft/min.

The figure ″PRESSURIZATION CONTROL SYSTEM - PRESSURIZA-TION DIAGRAM″ shows the operation of the system.



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AUTO PRESS

LAND ELEV (ft)ELV SET

+

-

DUMP AUTO/MAN

ON MAN

1

2

3

OVERPRESSURE RELIEF VALVE

NEGATIVE PRESSURE RELIEF VALVE

CABIN ALTITUDE LIMITER

PRESSURIZED AREA

REAR PRESSURE BULKHEAD

NON-PRESSURIZED AREA

THRUST LEVER

AIR/GROUND

ADC 1

ADC 2

DC BUS 136-10-00 36-10-00

1

2

31

2

145AMM210129.MCE A

PRESSURIZATION CONTROL SYSTEM - PRESSURIZATION DIAGRAM



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Documents

automatic mode of operation

manual controller

manual mode of operation

primary mode

digital controller tableref

fast depressurization

cabin rate of change

selection of man mode