Pressurization System

Gulfstream GVII

Eddie sez:

The standard pneumatic, air conditioning and pressurization systems brief applies here: the pneumatic system provides high pressure and temperature air, the air conditioning system makes that air tolerable in terms of temperature and pumps that into the cabin, and the pressurization system allows just enough of that air to escape to keep the cabin altitude livable. If you've flown any Gulfstream since the GV you will recognize much of these systems. But there are quite a few subtle differences which makes studying this a few times worth your while. The automatic mode, for example, is available all the way down to battery power. How is that possible? Unlike many previous Gulfstreams, the TROV is controlled by one of three DC motors, no more AC need by the TROV.

For a quick refresher or a good intro, be sure to see Ivan Luciani's notes: G500 Pressurization System Notes.

Everything here is from the references shown below, with a few comments in an alternate color.


Photo: G500 Pressurization system components, PAS, p. 15-5
Click photo for a larger image

How it Works . . .

The Components in Greater Detail . . .

Limitations and Abnormal Procedures . . .

Last revision:


How it Works . . .

Normal Operations

Cabin Pressurization Refresh Rate

[Gulfstream Journal]

  • All Gulfstream model aircraft utilize a 100% refresh rate, meaning that the air supplied to the occupants is never recycled and is replenished at a defined rate based on air volume supply and cabin volume. The attached chart depicts the air supply and the rate at which this airflow is replenished during a typical cruise altitude for specific models. The rate of cabin air exchange shows the cabin occupants are essentially always receiving a fresh, clean air supply.
  • In addition to this cabin air exchange rate, there are a few other items to consider putting minds at ease. The air supply being used comes from the engine high stage compressors. The engine compresses outside air to very high pressures and temperatures which will destroy impurities that may be in the air supply. The APU also compresses the airflow sufficiently providing a clean supply of air.
  • As the airflow continues through the environmental control system of the aircraft, there is yet another stage of compression taking place. As the air enters the environmental control units (aka air cycle machine), the air temperature is again raised before the rapid expansion stage takes place within the unit. This gives an additional cleaning to the supply of air before being supplied to the cabin occupants.

Photo: G500 Cabin refresh rate Gulfstream Journal
Click photo for a larger image

When Operating in Either Auto or Semi Mode


Photo: G500 Pressurization profile, PAS, p. 15-18
Click photo for a larger image

[PAS, pp. 15-17 to 15-18]

  • Pre-pressurization to 0.25 psid (approx LFE - 500')

    • 0.25 psid still allows opening of plug-type emergency exits.

    • Initiated if doors closed and: Pressure Profile switch selected to Flight, airplane taxis > 9 knots, or throttles advanced ≥ 15° thrust lever angle. If the Pressure Profile switch is set to Landing, the automatic return to Flight Profile will not occur. The main door must be opened and then closed to restore this automatic function.

  • The cabin rate of climb after takeoff is approximately 500 fpm. The final cabin altitude determined by CPCU based on the planned cruise altitude and the landing field elevation.

  • If the aircraft descends at least 1000' from cruise altitude, the system automatically switches to Landing profile. If there is a subsequent level off ≥ FL250, the system returns to Flight Profile after 3-6 minutes. The CPCS also switches to the descent pressurization schedule if the Pressure Profile switch is selected to Landing.

  • Descent pressurization schedule:

    • Cabin rate of descent → Approximately 150 fpm until cabin altitude 250' below landing field elevation (LFE).

    • When WOW = Ground, cabin climbs at 500 fpm for 1 min to depressurize.

    • PRV opens 1 min after TROV fully opens.

Manual Mode Operations

[PAS, p. 15-20]

  • To Operate in Manual Mode, depress FAULT / MANUAL switch → Amber MANUAL. The TROV will be controlled with rotation of CABIN ALT knob.

  • Monitor to maintain max 500 fpm cabin climb or descent, make only small control inputs on rotary knob. During descent, select the 11 o'clock position for 1 second then release. During climb, select the 1 o'clock position for 1 second then release. Wait for cabin rate of change response prior to next input.

  • Changes in engine thrust will affect cabin airflow and cause variations in cabin pressure and rates of change. The PF must coordinate with PM on power changes so PM can make timely inputs with the rotary knob.

Cabin Altitude Trip Points

[PAS, p. 15-21]

  • Landing Profile is based on Landing Field Elevation (LFE), where Trip point altitudes ↑ as LFE ↑

    • If LFE ≤ 7,500' the trip point is ≥ 8,000'

    • If LFE > 7,500' and < 9,500' the trip point is ≥ 10,000'

    • If LFE > 9,500' and < 14,000' the trip point is ≥ 14,500'

    • If LFE ≥ 14,000' the trip point is ≥ 15,500'

  • Flight Profile on the ground: trip point set to 1,000' above takeoff field elevation in the range → 8000' - 16,000'.

  • Flight profile after takeoff: the trip point resets in a constantly decreasing manner until it reaches 8000' or will reset to 8,000' once the altitude > FL340.

  • When LFE results in trip point > 10,000' you will get a Cab Alt Alert Exceeds 10K CAS message. (In Auto mode only).

The Components in Greater Detail . . .

Cabin Pressure Acquisition Module (CPAM)


Photo: G500 CPAM, PAS, p. 15-4
Click photo for a larger image

[PAS, p. 15-4]

  • The CPAM is the arbitrator used for comparison if CPCUs disagree.

  • The CPAM is the sole source when both CPCUs are inoperative or if manual mode is selected.

  • The CPAM provides data when acting as sole source to OHPTS Hyd/CPCS page and ECS/Press synoptic pages.

Cabin Pressure Control Panel


Photo: G500 Cabin Pressure Control Panel, PAS, p. 15-6
Click photo for a larger image

[PAS, p. 15-6]

  • The Cabin Pressure Control Panel is on the center right portion of Overhead Panel.

  • The FAULT / MANUAL switch:

    • Amber FAULT → Indicates failure of both CPCUs.

    • Selecting Amber MANUAL places the pressurization system into the manual mode. This gives you manual control of the TROV and provides a backup method if both CPCUs fail. The TROV will be controlled with rotation of CABIN ALT knob.

    • The CABIN ALT knob is spring loaded to HOLD position where the TROV will HOLD its current position. The further from HOLD you go, the faster the TROV moves. Move the knob left to DESCEND cabin altitude, closing the TROV. Move the knob right to CLIMB cabin altitude, opening the TROV.

    • If you select Manual then deselect, you will return the system to the last known mode, Auto or Semi, and change the active CPCU.

Cabin Pressure Control Units (CPCUs)


Photo: G500 Cabin Pressure Control Units (CPCUs), PAS, p. 15-2
Click photo for a larger image

[PAS, p. 15-2]

  • There are two Cabin Pressure Control Units (CPCUs), CPCU 1 and 2, beneath the cockpit floor, which are microprocessors that make all pressurization logic decisions.

  • Only one is in control at any time, the other is in standby. They switch roles after landing one minute after the WOW system goes to ground mode.

  • The CPCUs receive inputs from the flight crew (via TSC 1-4 and OHPTS's), cabin pressure sensors, and from the Air Data System (ADS).

  • The CPCUs control the Thrust Recovery Outflow Valve (TROV) when in AUTO or SEMI mode to regulate rate of climb and descent of cabin altitude.

  • Provides information displayed on OHPTS Hyd / CPCS page (normal ops): cabin altitude, cabin differential pressure, and cabin rate of change.

  • The Manual Motor Controller Unit (MMCU) allows for manual control of TROV when necessary and is controlled via CABIN PRESSURE CONTROL Panel on the overhead panel.

Manual Motor Control Unit (MMCU)

Work in Progress



Photo: G500 Pressurization system indicators, PAS, pp. 15-7 to 15-9
Click photo for a larger image

[PAS, p. 15-7]

Cabin Rate of Change Indicator:

  • Displays cabin altitude rate of climb or descent shown in ft/min from - 6000 to 6000.

  • In Auto and Semi modes data is provided by a CPCU. The nominal rate in Auto (Flight Profile) is approximately 500 fpm climb and 150 fpm descent.

  • The rate is selectable rate in Semi, from 0 to 3340 fpm climb and 0 to 2000 fpm descent.

  • In manual mode data is provided by the CPAM. It is up to the pilot to monitor to maintain a maximum rate of 500 fpm climb and 500 fpm descent.

Cabin Alt and Diff Press Indicators

  • Cabin Alt and Diff Press Indicators display current cabin altitude, current cabin differential pressure in psi, and trend arrows.

  • Mode indication displays current mode of system and active CPCU if applicable: Auto 1, Auto 2, Semi 1, Semi 2, or Manual.

System Mode Soft Switch

  • The System Mode Soft Switch displays current mode of system. The default position on power up is Auto.

  • When pressed, the CPCU is toggled between Auto and Semi modes.

  • In Auto mode, the CPCUs control pressure based on a pressurization schedule with input from FMS data.

  • In Semi mode, the crew must input relevant data via TSCs 1-4 CPCS page. Once all relevant data is entered, the CPCU automatically controls pressurization. If no selection is made, CPCS keeps to AUTO pressurization schedule. Semi mode is used when FMS data not available or is invalid, at crew discretion (e.g., QFE ops), or when the checklist directs (e.g., Smoke and Fumes Evacuation).

  • Manual mode is selected via overhead CABIN PRESSURE CONTROL Panel. The OHPTS soft switch grays out to indicate Manual mode.

Pressure Profile Soft Switch

  • The Pressure Profile Soft Switch indicates current operating status of CPCU (Landing or Flight mode) and allows manual selection of Flight or Landing modes.

  • When the pressurization system is in Auto or Semi-Auto mode, landing mode is automatically entered as the default mode on power up or when the aircraft descends 1000' from cruise altitude. If an intermediate level off occurs ≥ FL250, the system re-enters Flight mode 3-6 minutes after level off. With the main door closed, flight mode is automatically entered when FMS ground speed > 9 knots or the throttles are advanced ≥ 15° throttle lever angle.

TROV Position Indicator

  • An indicator only, not a slider, represented by 2 opposing open triangles.

  • Indicates relative position of TROV in all modes, from CLSD to OPEN with arrows indicating direction of movement.

  • Functional in all pressurization modes of operation.

Pressure Relief Valve (PRV)


Photo: G500 TROV, PAS, p. 15-3
Click photo for a larger image

[PAS, p. 15-3]

  • The Pressure Relief Valve (PRV) is located just above TROV and provides a rate-limiting function to prevent aircraft damage from:

    • Excessive positive pressure at two metering levels (10.8 and 11.0 psid).

    • Excessive negative pressure → -0.25 psid (No CAS msg)

  • The PRV uses independently sensed cabin pressure using aircraft static ports.

  • On the ground when the TROV is fully open, the PRV also opens to ensure a minimum psid within pressure vessel 1 min after touchdown unless in the manual mode.

  • In Flight the PRV automatically closes when the bleed air switches are OFF, to help minimize the pressure vessel leak rate.

Pressurization System Static Ports


Photo: G500 Pressurization system static ports, PAS, p. 15-4
Click photo for a larger image

[PAS, p. 15-4]

  • There are three pressurization system static ports on the right fuselage forward of the wing.

  • Two are for the PRV that provide static press information to the 10.8 psid relief section and the 11.0 psid relief section. One, the smaller of the three, is for the CPAM.

Thrust Recovery Outflow Valve (TROV)


Photo: G500 TROV, PAS, p. 15-3
Click photo for a larger image

[PAS, p. 15-3]

  • The TROV has a butterfly plate which opens and closes to manage escape of cabin air. The escaping air directed aft along fuselage to minimize drag. It is driven by one of three DC motors, two through the CPCUs in auto and semi-auto modes, and a third through MMCU in manual mode.

  • On the ground the TROV automatically opens when the APU Master is switched ON or either fuel control switch is set to RUN. It automatically closes when the fuel control switches and APU Master switch is set to OFF.

  • In flight the TROV automatically closes when the bleed air switches are turned OFF, this helps minimize the pressure vessel leak rate.

Limitations and Abnormal Procedures


[G500 AFM, §01-21-10]

    1. Landing Field Elevation (LFE)
      1. Limited to less than 10,000 MSL with the CPCS in Semi Mode except during an emergency.
    2. Maximum Cabin Differential Pressures
      1. In Flight: 10.69 PSI
      2. Taxi, Takeoff, Landing: 0.3 PSI
    3. ECS Duct Temperatures
      1. Duct temperatures above 200°F (93°C) are prohibited during manual zone control.
    4. ECS Pack Operation
      1. During ground operations with SAT greater than 98°F (37°C), a minimum of one ECS pack must be operating with APU or Engines operating.
    5. Single Pack Operation
      1. Must comply with 03-01-10, Pack Failure - Single.

See Also:

Gulfstream Cabin Refresh Rates, Gulfstream Journal, May 15, 2020

Gulfstream GVII-G500 Airplane Flight Manual, Revision 4, August 29, 2019

Gulfstream GVII-G500 Production Aircraft Systems, Revision 3, July 15, 2019