citation mustang pressurization

GENERAL Two elements provide cabin pressurization.One is a constant source of pressurized bleedair to the cabin (Figure 12-1). The other is amethod of controlling outflow of the pressur-ized air from the cabin to achieve the desireddifferential pressure (between cabin and out-side air pressure) and resultant cabin pressure(“cabin altitude”). The maximum cabin pres-sure differential is 8.6 psid. Normal cabin pres-

sure differential is 8.3 psid. This permits an8,000-foot cabin altitude at a 41,000-foot ac-tual altitude (FL 410).

On the Citation Mustang, pressurization isprovided by the combined action of two cabinair systems: inflow and outflow. Inflow is sup-plied by temperature-controlled pressurizedbleed air and regulated cabin air outflow.

INTRODUCTIONThe pressurization system on the Citation Mustang maintains cabin altitude lower thanthe actual aircraft altitude to provide a suitable environment for the crew and passen-gers. To accomplish this, the pilot directs a constant supply of conditioned bleed air intothe cabin (pressure vessel), then controls the amount of air allowed to escape overboardby automatic controls (with manual override).

CITATION MUSTANG OPERATING MANUAL

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CHAPTER 12PRESSURIZATION


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The conditioned air system continuously sup-plies pressurized, conditioned air to the cabin.This provides positive inflow. Bleed-air inflowto the cabin is fairly constant through a widerange of engine power settings. (Refer toChapter 11—“Air Conditioning”)

The pressurized cabin air then escapes throughnormal leakage in the cabin pressure vessel andthrough the two outflow valves in the aft pres-sure bulkhead.

The outflow valves exhaust cabin air into thetail cone (which is vented to the outside) muchfaster than normal cabin leakage. This providesregulated cabin air outflow. The balance be-tween inflow and outflow establishes cabinpressure.

Two outflow valves on the aft pressure bulk-head control the outflow of cabin air. The out-flow valves vary between open and closed toincrease or reduce outflow.

When the outflow valves are more open, in-flow air escapes the cabin rapidly, reducingcabin pressure. This increases cabin altitude(the cabin “climbs”).

When the outflow valves are more closed, in-flow air remains in the cabin longer, increas-ing cabin pressure. This decreases cabinaltitude (the cabin “dives”).

On the ground, the outflow valves open fully,putting the cabin at ambient pressure. Thisensures that doors open easily and preventssudden pressure changes when they areopened.

The outflow valves are controlled pneumati-cally. Automatic control requires normal DCpower and is not available during emergencyelectrical power operations. Additionally,safety valves operate regardless of the avail-ability of other systems.

Selecting AUTO mode generates an automaticcabin altitude schedule (autoschedule) based on:

• Departure field elevation

• Maximum altitude reached

• Pilot input of destination elevation(DEST ELV)

After takeoff, the pressurization system at-tempts to maintain a cabin altitude equal to de-parture elevation until cabin differentialpressure reaches 8.3 psid. Then the pressur-ization system reverts to the autoschedule.

The pressurization controller has two modes ofoperation, normal and high altitude. High-al-titude mode is discussed later in this chapter.

DESCRIPTIONThe pressurization system includes controllingpressurized cabin air outflow and the associ-ated valves, controls, indications, pneumaticlines, and electrical circuits (see Figure 12-1).

The pressurization outflow system includes thefollowing components:

• Outflow valves (with associated con-trol and safety valves)

• Pressurization controller

• Pressurizat ion system controls and display

To provide system redundancy, each outflowvalve contains a maximum differential pres-sure limiter valve and a maximum cabin altitudelimiter valve. These valves ensure the cabinpressure remains within safe limits. Outflowvalves, operated manually by the CABIN DUMPswitch and automatically by the pressurizationcontroller, provide control of the pressuriza-tion system. The system authority in descend-ing order of control is as follows:

• Maximum cabin altitude limiter

• Maximum differential pressure limiter

• CABIN DUMP switch

• Pressurization controller

COMPONENTS

OUTFLOW VALVESThe outflow valves release air from the cabinat a regulated rate. This establishes the pres-sure balance between inflow and outflow, andresulting cabin pressure (“cabin altitude”).The outflow valves are controlled by variousregulating valves that connect to (or are builtinto) the outflow valves (see Figure 12-1).

Outflow Valve BasicsTwo outflow valves regulate the outflow ofpressurized cabin air through two openings inthe aft cabin pressure bulkhead. This regulatedoutflow controls cabin pressure differential(Delta-P) and resulting “cabin altitude.” Eachoutflow valve opens or closes its respectivecabin opening with a flexible diaphragm. Thediaphragm is on the back of a hollow controlchamber (Figure 12-2). When the outflowvalve control chamber inflates, the diaphragmon the back side of the valve expands, reduc-ing the cabin opening. This restricts airflowbetween the cabin and outside air.

When the outflow valve control chamber de-flates, the diaphragm pulls back from the cabinopening and exposes more of it, allowing moreair to move through the opening between thecabin and the outside (tail cone). Outflowvalves normally are partially open, providinga limited outflow of cabin air, and a controlledcabin pressure differential, resulting in a con-trolled cabin altitude.

The outflow valves synchronize with eachother through a pneumatic link. The controlchambers of the two outflow valves alwayshave the same pressure because they are pneu-matically connected. Consequently, each out-flow valve duplicates the action of the other.This feature balances the cabin air outflow ofthe two valves (see Figure 12-1).

Outflow Valve RegulationMultiple regulating valves are built into eachoutflow valve. These valves regulate the airpressure in the outflow valve control chamberand thereby control the diaphragm position.This regulates cabin pressure outflow (seeFigure 12-1). The regulating valves include:

• Dive solenoid valve (with dive pump)

• Climb solenoid valve (with climb pump)

• Maximum differential pressure limiter(maximum Delta-P) valve on each out-flow valve

• Maximum cabin altitude safety limitervalve on each outflow valve

Climb and Dive Solenoid ValvesThe two solenoid valves (dive solenoid valveand climb solenoid valve) open or close oncommand of the pressurization controller. Thisregulates the control-chamber pressure anddiaphragm position on the outflow valves,which control cabin air outflow.

Dive Solenoid ValveWhen the pressurization controller energizesthe dive solenoid valve open, it allows cabinair to enter the outflow valve control chamber,inflating the chamber and causing the di-aphragm to expand, which restricts the cabinopening (see Figure 12-2). If bleed air enter-ing the cabin cannot escape as fast as it enters,then the cabin pressurizes (dives).

Climb Solenoid ValveWhen the pressurization controller opens theclimb solenoid, air escapes from the outflowvalve control chamber to an ambient staticpressure line. As air is drawn out of the con-trol chamber, the outflow valve diaphragmcontracts. This exposes the cabin opening, al-lowing increased airflow between the cabin andthe outside, which reduces cabin pressure(cabin altitude climbs).


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Electrical Failure ModeIf all DC power is lost, the dive and climb so-leno id va lves fa i l in a c losed pos i t ion .Pressurization is then limited automaticallyby the maximum Delta-P valve and maxi-mum cabin altitude limit valve (which arenot affected by electrical power). Under theseconditions, if the aircraft descends to an ac-tual altitude equal to cabin pressure altitude,the outflow valves are forced open by outsideair, which enters the cabin, equalizing thepressure and maintaining the cabin at actualaircraft altitude.

If normal DC power is lost and emergencypower is available, both solenoids fail closed;however, the climb solenoid can still be oper-ated manually with the CABIN DUMP switch.

Maximum Cabin Altitude LimitValvesThe maximum cabin altitude limit valves (onein each outflow valve) automatically preventcabin pressure altitude from exceeding 14,300± 300 feet.

Inside the valve, a sealed bellows, similar tothe aneroid chamber in an altimeter, main-tains a constant reference pressure, related tothe cabin altitude ceiling of approximately14,300 feet. The bellows puts pressure on thevalve to open it. A spring pushes in the oppo-site direction to hold the valve shut with helpfrom cabin air pressure.

However, if cabin altitude rises above 14,300feet, cabin pressure drops, and is not enough tohold the valve closed. The sealed bellows ex-pands and pushes the maximum cabin limitvalve open. This allows cabin pressure into theoutflow valve control chamber, increasing pres-sure in the control chamber, which causes its di-aphragm to expand and restrict the outflowvalve cabin opening. Restricting the cabin open-ing limits outflow. If adequate pressurizationsource air is still available (as selected by AIRSOURCE SELECT knob set to BOTH, L or R),cabin inflow is greater than cabin outflow, andcabin pressure altitude drops to 14,300 ± 300feet or lower, and stays below that limit.

This valve is not dependent upon electricalpower, and overrides all other pressurizationsystem controls.

Maximum Differential Pressure(Maximum Delta-P) Limiter ValvesIf cabin pressure exceeds 8.6 psid, the maxi-mum differential pressure valves (one on eachoutflow valve) open automatically, which re-leases pressure from each outflow valve con-trol chamber. The diaphragm contracts, whichreleases pressure from the cabin. As a result,cabin altitude climbs, reducing cabin pres-sure differential until reaching a differentialpressure of 8.6 psid.

The maximum differential pressure limitervalves override all other pressurization system

Figure 12-2. Outflow Valve Positions

CABIN AIR FREELYFLOWS TO TAIL CONE

DIAPHRAGMRELAXED OPEN;

NO PRESSURIZATION

CABIN AIRFLOW TOTAIL CONE RESTRICTED

DIAPHRAGM INFLATED;SOME DIFFERENTIAL

PRESSURE DEVELOPING

DIAPHRAGMVACUUMED OPEN;

NO PRESSURIZATION

CABIN

AFT PRESSUREBULKHEAD

TAIL CONE

controls, except the maximum cabin altitudelimit valves, and are not dependent upon anyother system, nor any control.

CONTROLS ANDINDICATIONSAll pressurization system controls are on theENVIRONMENTAL panel immediately to theright of the throttle quadrant (Figure 12-3), ex-cept for DEST ELV settings (which are se-lected through the PFD softkeys). Indicationson the EICAS in the CABIN PRESS display(Figure 12-4) and CAS messages indicate theconditions and performance of the pressur-ization system. CAS messages warn the pilotof abnormal and emergency situations.

PRESSURIZATIONCONTROLLERThe pressurization controller has two modes ofoperation, normal and high altitude. Dependingon aircraft altitude and various factors, the con-troller commands appropriate auto schedules asneeded. In response to ambient air data from the

aircraft avionics system, and settings by thepilot, the controller regulates cabin pressure byelectrical signals to the climb and dive sole-noid valves (see Figure 12-1). The pressuriza-tion controller maintains an 8,000-foot cabinaltitude up to 41,000 feet with a cabin pressuredifferential of 8.3 psid (± 0.1).

The pressurization controller has a built-inschedule that automatically

• Controls cabin altitude based on aircraftaltitude

• Adjusts cabin rate of climb/descent ver-sus aircraft rate of climb/descent

• Adjusts for destination elevation as se-lected by the pilot


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Figure 12-3. Pressurization Controls

ALTITUDERATE

CABINALTITUDE

CABINALTITUDE(DIGITAL)

ALTITUDERATE(DIGITAL)

DIFFERENTIALPRESSURE

DESTINATIONELEVATION

DIGITAL DIFF PSI

Figure 12-4. Standard (MFD)Pressurization Display

The controller receives air data informationfrom air data computers through the G1000Garmin Interface Adapter (GIA) No. 1.

DESTINATION ELEVATIONSETTINGThe pilot sets the destination elevation throughcontrols on either G1000 PFD, using theTMR/REF softkey, FMS knobs, and ENT but-t on . The p rocedu re i s de sc r ibed i n t heOperation section.

PRESS CONT (STANDBY—NORM) SWITCHThe PRESS CONT switch on the PRESSUR-IZATION subpanel of the ENVIRONMEN-TAL control panel (see Figure 12-3) selects themode of operation in flight. When NORM isselected, the pressurization controller automat-ically functions to control cabin altitude inflight mode. When the pilot selects STANDBY,pressurization operates in a pneumatic backupmode in flight. With the PRESS CONT switchin either position, the CABIN DUMP switchremains functional.

MANUAL CABIN DUMP SWITCHThe CABIN DUMP switch on the PRESSUR-IZATION subpanel (see Figure 12-3) can bemanually actuated at any time DC or EMERpower is available to reduce cabin pressure.The switch relieves cabin pressure by energiz-ing the climb solenoid valve open, which re-leases regulated air from the outflow valvecontrol chambers. This retracts the outflowvalve diaphragms, opening the outflow valves,and releases pressure from the cabin.

The maximum cabin altitude limit valves over-ride the climb solenoid valves to prevent cabindepressurization above 14,300 ± 300 feet al-titude. The cabin dump system requires DCpower. The switch and associated climb sole-noid are powered by the emergency bus.Circuit protection for the CABIN DUMP is on

the right CB panel in the ENVIRO groupinglabeled “CABIN DUMP” (see Figure 12-1).

The CABIN DUMP switch is protected fromaccidental operation by a red guard. To oper-ate the switch, lift the red guard and press andrelease. The switch is a latching switch. Whenpressed, the lighted switch indication changesfrom NORM to DUMP. Pressing again re-stores the switch back to NORM.

PRESSURIZATION DISPLAYThe pressurization display is labeled CABINPRESS, and normally appears on the lower sec-ond column of the EICAS on the MFD (seeFigure 12-4). It indicates:

• The label “CABIN PRESS”

• Cabin altitude (ALT FT)

• Cabin altitude rate-of-change (RATEFPM)

• Destination elevation (DEST ELV)

• Cabin differential pressure (DIFF PSI)

If any indication is disabled by invalid data,a red “X” replaces that specific indication. Ifthe data is out of range of a digital readout, thedigits are dashed out.

In reversionary mode or emergency powermode, the pressurization display (Figure 12-5)is limited to three lines showing:

• The label CABIN PRESS,

• Cabin altitude (ALT FT with digitalreadout), and

• Cabin differential pressure (DIFF PSIwith a digital readout).

Cabin Altitude: ALT FTCabin pressure altitude (in feet) is indicatedunder the label “ALT FT,” on a vertical ana-log display and a digital readout. In rever-sionary mode or emergency power mode, onlythe digital readout appears. When the aircraft


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is on the ground, the digital readout does notappear and the analog display bar is all green.

The analog display scale pointer when thecontroller is in normal mode is:

• Red above 10,000-foot cabin altitude

• Amber between 8,500- and 10,000-footcabin altitude

• Green below 8,500-foot cabin altitude

The analog scale labels are white and thepointer changes color depending on the colorrange to which it is pointing.

If the system detects cabin altitude beyondthe limits of the display (0–15,000 feet cabinaltitude), the pointer goes to the appropriateend of the scale and points away from the cen-ter. If the system has invalid data, a red “X”replaces the digital readout. If both squatswitches indicate the aircraft is on the ground,the digits disappear.

Cabin Altitude Rate-of-Change:RATE FPMCabin pressure altitude rate-of-change (in feetper minute) is normally indicated under thelabel “RATE FPM” on a vertical analog dis-play and a green pointer and digital readout. Thisindication reports the rate of change of cabin al-titude, not actual aircraft vertical speed. In re-versionary mode or emergency power mode,this indication does not appear on the pressur-ization display,

The analog scale and its markings are white, andthe pointer is green. The scale is marked at:

• +1 (1,000 fpm cabin climb rate)

• 0 (cabin altitude not changing)

• –1 (1,000 fpm cabin descent rate)

If cabin rate exceeds the range of the analogscale, the pointer goes to the appropriate endof the scale and points away from center. If thesystem has invalid data, a red “X” is displayed.The cabin rate on the ground is zero (0), ex-cept during prepressurization.

Destination Elevation: DESTELVIn normal display mode, the altitude of the des-tination airport (in feet), as selected by thepilot, is indicated by a digital readout in frontof the white label “DEST ELV.” In reversion-ary mode or emergency power mode, this datais not displayed on the pressurization display,but can a lways be accessed through theTMR/REF menu on the PFD.

The DEST ELV digits are cyan and may be setto any altitude between –1,000 and 14,000 feet.

This setting is retained by the G1000 systemwhen the aircraft is powered off. When theaircraft is powered on again, the value fromthe previous flight remains set in the systemuntil changed by the pilot.


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Figure 12-5. Pressurization Display(Reversionary Mode)

Cabin Differential Pressure:DIFF PSIThe cabin differential pressure indication is atthe bottom of the pressurization display, labeled“DIFF PSI.” It indicates the difference (in psid)between cabin pressure and outside air pres-sure. Normally, it is displayed as a horizontalanalog display and digital readout. In reversion-ary mode, only the digital readout appears withthe DIFF PSI label. (If all air data is lost, a red“X” replaces the digital readout.)

The scale and pointer are green below 8.6 psidand red at 8.6 psid or higher. If pressure reaches8.6 psid or higher, the digital readout andpointer turn red. Maximum cabin pressure dif-ferential (maximum Delta-P) valves automat-ically prevent this from happening.

If cabin differential pressure is less than 0.2psid, 0.0 psid is displayed.

CAS MESSAGESThree CAS messages (in different colors, de-pending on conditions) provide information onthe pressurization system:

• CABIN ALT (unsafe cabin altitude)

• PRESS OFF (pressurization air inflowis shut off)

• PRESS CTRL (pressurization controlleris disabled)

CABIN ALT The CABIN ALT message indicates an unsafecabin altitude. The message is controlled byinputs from two cabin pressure sensors. Eithersensor can activate the message. The CABINALT message is either red, amber, or white de-pending on specific conditions.

In flight, the red CABIN ALT message appearswhen the cabin altitude is above a maximumof 10,000 feet, except when the pressurizationsystem is set for high-altitude mode.

NOTEHigh altitude mode changes theseindications. (Refer to High AltitudeMode later in this chapter.)

However, any time the aircraft is in flightabove an actual altitude of 25,000 feet, if thecabin altitude rises above 10,000 feet, the redCABIN ALT message appears. The messagedisappears when cabin altitude descends below8,300 feet.

In flight, the red CABIN ALT message also ap-pears any time the cabin altitude is above ap-p rox ima te ly 15 ,000 f ee t . The messagedisappears when cabin altitude descends below11,000 feet.

If the aircraft is on the ground, as indicated bya squat switch, the CABIN ALT message is notdisplayed, regardless of cabin altitude (ex-cept during the rotary test procedure). Duringrotary test, when the rotary TEST knob is ro-tated to the CABIN ALT position, the amberand red CABIN ALT messages both appear inthe CAS display.

PRESS OFF The white PRESS OFF message indicates thatthe AIR SOURCE SELECT knob is set to OFFor FRESH AIR, either of which stops pressur-ized air inflow to the cabin. The cabin slowlydepressurizes (due to normal cabin leakage)until pressure is equalized between cabin andoutside air. At this point, if FRESH AIR is se-lected, the fresh-air duct opens and a fan in-jects unpressurized outside (fresh) air into theaircraft.

PRESS CTRL The white PRESS CTRL message indicatesfailure of the ARINC 429 data link from theG1000 system, indicating that the controllermay no longer have valid data on outside airpressure, actual aircraft altitude, or selecteddestination elevation.


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The amber PRESS CTRL message indicatesfailure of the pressurization controller or thatthe pilot has selected the PRES CONT switchto STANDBY, disabling the pressurizationcontroller.

If the message is amber, the pressurizationcontroller no longer has valid control of theoutflow valves, and the climb and dive sole-noid valves close. The system begins to op-erate in pneumatic mode. The outflow valvescause the cabin altitude to move oppositethe direction of aircraft movement. If theaircraft climbs, the cabin dives (and viceversa).

If aircraft actual altitude rises high enough toexceed 8.6 psid, the maximum cabin differen-tial valves open and the cabin altitude in-creases as needed to maintain 8.6 psid. Ifaircraft actual altitude descends to the cabinaltitude, the outflow valves open allowingoutside air to enter the cabin, which equalizescabin altitude with actual altitude.

OPERATIONThe AIR SOURCE SELECT knob provideslimited control of incoming air pressure fromthe engine bleed-air system. For pressurization,the control must be set to receive bleed airfrom an operating engine (L, R, or BOTH).All functions of this control are detailed inChapter 11—“Air Conditioning.”

Pressurization also may be controlled manu-ally with the CABIN DUMP switch if DC orEMER power is available.

GROUND/FLIGHT MODESCabin pressure is maintained by controllingthe outflow of air from the pressure vessel.A maximum cabin differential pressure of 8.6psid is permitted for the pressure vessel. Themaximum cabin pressure differential allowedby limiters on the outflow valves is 8.5 ±0.1 psid. Squat switches and engine throttle

lever settings are used to define four oper-ating modes:

• Ground/taxi mode

• Prepressurization mode

• Flight mode (including high altitudemode)

• Pneumatic mode

Ground/Taxi ModeOn the ground (as detected by a squat switch)with both engines operating below CRU throt-tle settings (approximately 85% N2), both out-flow valves are kept fully open. This equalizesthe pressure between cabin and ambient air,makes opening doors easier, and avoids pres-sure bumps when doors are opened.

Prepressurization ModeWhen either engine is set to the CRU throttle set-ting or higher (greater than approximately 85%N2) on the ground, both outflow valves slowlyrestrict to bring cabin pressure difference to amaximum of 200 feet below field altitude. Thisis normal operation during takeoff roll. (Atliftoff, the squat switches put the system intoflight mode.)

Flight ModeDuring flight (as detected by the squat switches),the pressurization controller operates the climband dive solenoids to maintain cabin altitude andto provide a gradual cabin climb to cruisingcabin altitude. During aircraft descent, the con-troller manages a gradual cabin descent towardaircraft destination airport elevation.

When the PRESS CONT switch (see Figure 12-3) is in the NORM position, the pilot normallyselects destination field elevation using theSetting Destination Elevation procedure, notedbelow (accomplish during the “Before Taxi”checklist).

In flight, the pressurization controller contin-uously generates an autoschedule based on:

• Departure field elevation

• Maximum altitude reached in the currentflight (per the air data computer (ADC))

• Pilot-input destination elevation

The pressurization controller determines pres-sure rate of change and cabin pressure altitudebased on autoschedule and the ADC pressurealtitude. The pressurization controller sendsDC pulses to the climb and dive solenoids toadjust the outflow valves (to obtain a specificcabin pressure). Before touchdown, the au-toschedule completely depressurizes the cabin.

During climb, the automatic mode limits thecabin pressurization rate from exceeding ap-proximately 600 fpm regardless of the air-craft climb rate.

NOTEIt is possible for the aircraft to climbfast enough to “out climb” the auto-matic cabin pressure controller canreach an altitude where the maximumcabin differential pressure (maximumDelta-P) of 8.6 psid is reached beforethe aircraft reaches its cruising alti-tude. In this case, the maximum cabindifferential pressure limiter (maxi-mum Delta-P) valves are forced openby the cabin differential air pressurepartially opening the cabin outflowvalves. This releases cabin pressureand causes the cabin to climb at thesame rate as the aircraft until reach-ing cruising altitude.

Likewise, during normal descents, the auto-matic mode limits cabin depressurization ratesto less than 500 fpm regardless of the aircraftdescent rate. The system corrects rapidly tosmall cabin pressure variations to prevent pilotand passenger discomfort.

NOTEBecause the aircraft can descendfaster than 500 fpm, it is possible to“catch the cabin” on the way downduring a rapid descent, thus forcinga cabin descent rate greater than 500fpm. In this event, when the aircraftdescends to the current cabin alti-tude (somewhere below 8,000 feet)momentarily resulting in zero pres-sure differential, it reverts to func-tioning as an unpressurized aircraft.For the rest of the descent, the cabinaltitude decreases at the same rateas the actual aircraft altitude.

During descent, as the aircraft descends 500feet below cruise altitude, the cabin begins torate down toward DEST ELV. The cabin shouldreach DEST ELV when the aircraft is 1,500 feetabove landing field elevation and maintainthis altitude until landing.

Prior to landing, the cabin is completely de-pressurized if the proper landing field eleva-tion has been set by the pilot and is indicatedin the DEST ELV display (see Figure 12-4).If the cabin is pressurized at landing, when theaircraft lands (causing squat switch input) andthrottles are reduced to below approximately85% N2, the cabin begins to depressurize at arate of 1,000 fpm for 30 seconds. After 30seconds, any residual cabin pressure is dumpedby the controller, which drives the outflowvalves fully open.

The pressurization controller uses aircraft al-titude and the altimeter barometric correctionfrom the Garmin G1000 to determine the cabinaltitude. If the communication between theG1000 and the controller is interrupted,changes to DEST ELV may not be received bythe pressurization controller. The controlleruses the last entered destination elevation,and the pressurization static pressure sourceto control cabin altitude. The autoschedule isnot interrupted, but a white PRESS CTRLmessage appears, indicating the data may notbe available to the pressurization controller.


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If landing at a different airfield altitude is de-sired, the cabin must be dumped using theCABIN DUMP switch before landing. If thedata link is restored, the CAS message disap-pears, and the controller recognizes the cur-rently entered DEST ELV as indicated on theEICAS display.

Pneumatic ModeThe pressur iza t ion cont ro l le r goes in tostandby mode if the controller detects an in-ternal fault or the PRESS CONT switch is setto STANDBY. An amber PRESS CTRL mes-sage appears on the MFD to advise the pilotthe pressurization system is in standby mode.In level flight the outflow valves maintainthe cabin altitude. The outflow valves causethe cabin altitude to move opposite the direc-tion of aircraft movement; if the aircraftclimbs, the cabin dives and vice versa. As theaircraft climbs, the cabin altitude decreasesuntil stopped by maximum differential pres-sure limiter valves. As the aircraft descends,cabin altitude increases until stopped by themaximum altitude limit valve (14,300 ± 300feet). The pilot cannot control cabin altitudeexcept by dumping the cabin with the CABINDUMP switch.

In pneumatic mode, pressure is trapped in themixing section of the outflow valves. As theaircraft climbs, the diaphragm expands andcloses off a larger portion of the outflow area,causing the cabin altitude to descend. As theaircraft descends, the diaphragm contractsand opens a larger portion of the outflow area,causing the cabin altitude to climb. In eithercase, the maximum altitude limiters and themaximum cabin differential limiters preventthe aircraft from passing through cabin pres-sure safety limits when the aircraft is operatedwithin the aircraft operating limitations as de-fined in the AFM.

SETTING DESTINATIONELEVATIONThe pilot sets the destination elevation throughthe TMR/REF softkey on the pilot PFD byusing the following procedure:

1. Push TMR/REF softkey on the PFD.

2. The reference window appears on thePFD screen.

3. Use the large FMS knob to select DESTELV.

4. Use small FMS knob to change number.

5. Press ENT button to accept the entereddestination elevation.

HIGH-ALTITUDE AIRPORTOPERATION (AUTOSCHEDULE)

High-Altitude LandingsWhen the aircraft is to land at an airfield be-tween 8,000 and 14,000 feet, certain conditionsmust be met before the controller automaticallyswitches into the high-altitude mode. The re-quired conditions are as follows:

• Selected landing altitude is greater than8,000 feet.

• G1000 data indicates aircraft altitudeis between 8,000 and 25,000 feet.

• Aircraft descends 500 feet from maxi-mum altitude (as determined by con-troller static sensor and GIA).

If the above conditions are true, then high al-titude airport mode is initiated. When landingat a high altitude airport, cabin pressure alti-tude does not exceed 8,000 feet before theaircraft altitude descends below FL 245. Upondescending past FL 245, the cabin altitudeclimbs at the increased climb rate, until the se-lected landing altitude is reached.


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High-Altitude DeparturesWhen the aircraft departs from an airfield be-tween 8,000 and 14,000 feet, a different setof conditions must be met before the con-troller can switch into the high-altitude mode.The required conditions are as follows:

• Weight on wheels

• G1000 data indicates aircraft altitudeis greater than 8,000 feet

• Cabin altitude is greater than 8,000 feet

High-Altitude CABIN ALTMessageWhen the conditions for high-altitude depar-tures or landings are met, the color of theCABIN ALT message changes to:

• White, with a cabin altitude between10,000 feet and 15,000 feet for not morethan 30 minutes.

• Amber, with a cabin altitude between10,000 feet and 15,000 feet for morethan 30 minutes.

• Red , if cabin altitude is at or above14,800 ± 200 feet.

• Red , if cabin altitude is at or above10,000 feet and the aircraft altitude isabove 25,000 feet.

Annunciation is inhibited on the ground andduring takeoff and landing.

High-Altitude Ranges forPressurization DisplayWhen in high-altitude mode, the color bandson the pressurization analog display changefrom their normal ranges to ranges appropri-ate for high-altitude operations (Figure 12-6).

The analog display scale when the controlleris in high altitude mode are:

• Red above 14,600-foot cabin altitude

• Amber between 14,000- and 14,600-footcabin altitude

• Green below 14,000-foot cabin altitude

MANUAL CABIN PRESSUREDUMPManually actuate the CABIN DUMP switch(see Figure 12-3) at any time DC or EMERpower is available to reduce cabin pressureand rapidly ventilate the cabin. The maximumaltitude limit valves override the climb sole-noid valves to prevent complete cabin depres-surization above 14,300 ± 300 feet altitude.

EMERGENCY/ABNORMALFor specific information on emergency/abnor-mal procedures, refer to the appropriate abbre-viated checklists or the FAA-approved AirplaneFlight Manual (AFM).

CABIN PRESS

X1000+1

ALT FT RATE FPM

DEST ELV

DIFF PSI

0 5 10

09930

0.09930

0

-10

5

10

15

Figure 12-6. Cabin Pressure Display

citation mustang pressurization

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