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Pneumatic System Abnormals

Gulfstream G450 Abnormals

As is also true with the air conditioning system: "If it is hot or failed turn it off." What follows is a list of the systems and another list of various things that can go wrong.


 

ACS Fail

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Figure: G450 Air Conditioning Flow Schematic, from FlightSafety International G450 Pilot Training Manual, figure 21-2.

If you look at the Flight Manual procedure for dealing with the ACS FAIL, L-R, you get the impression this will cause you to lose pressurization immediately, you need to immediately perform an emergency descent, and if you live through all that, you might try resetting the air conditioning controllers. But consider this:

  1. Even if you lose both air conditioning systems, the cabin should hold its pressure for a few minutes. (They say the cabin leak rate is no more than 1,000 fpm, but that isn't written anywhere.)
  2. Electrons are only used to turn the pack on (through the pack inlet valve), measure its performance, and set operating parameters. All of that is done through the Air Conditioning Controller.

Part of the problem is the AFM/QRH procedure is called "ACS Fail," that is Air Conditioning System Failure, but the procedure talks only of "pack failure." No wonder we think it is the pack that has failed. So, having said all that, here is the AFM procedure followed by pure technique. I know what I'm going to do, you need to decide for yourself.

Symptoms

ACS Fail, L-R

You may or may not see a change in the synoptics or the overhead panel, the indicated air conditioning pack switch may indicate it is OFF. If you really have two pack failures, you should notice a change in pressurization.

Analysis

[G450 Maintenance Manual, §21-51-00, ¶3.A.] The Air Conditioning Controllers (ACCs) provide automatic and manual temperature control of the forward and aft cabin zones and the cockpit zone and control of the left and right air conditioning packs. The left ACC contains two independent zone control channels. The zone 1 channel is used to control the temperature in the forward cabin zone. The zone 2 channel is used to control the temperature in the AFT cabin zone. The right ACC contains two independent zone control channels. The zone 1 channel is used to control the temperature in the cockpit zone. The zone 2 channel is unused.

The air conditioning packs are purely mechanical. An ACS Fail message is more than likely a computer problem: the Air Conditioning Controller (ACC). The QRH pulls and resets the circuit breakers for these as a last step "if time permits."

Procedure

[G450 Airplane Flight Manual, page 03-118]

  • If only a SINGLE pack is believed to have failed:
    1. Select affected pack to OFF.
    2. See 03-01-10, Single Air Conditioning Pack Failure.
    3. That procedure has two steps, turn the associated pack off and make sure the other pack has 35 psi.

  • If BOTH L and R packs are believed to have failed:
    1. Don crew O2 masks, and deploy PAX O2 masks.
    2. Prior to selecting any packs to OFF, start emergency descent.
    3. Perform emergency descent procedure. See Section 04-21-20, G450 Emergency Descent Procedure.
    4. If time permits and system is required for continued safe flight and landing, pull and reset the following circuit breakers simultaneously:
      1. For L ACS Fail: L PACK CONT: LEER, D-10 CAB AUTO TEMP: LEER, E-11
      2. For R ACS Fail: R PACK CONT: REER, D-9 CKPT AUTO TEMP: REER, E-8

Technique

  1. If you are losing cabin pressure at a rapid rate and you are at an altitude that will require passenger oxygen, execute an emergency descent.
  2. See: G450 Emergency descent.

  3. Identify the failed ACS system, pull and reset the following circuit breakers simultaneously:
    1. For L ACS Fail: L PACK CONT: LEER, D-10 CAB AUTO TEMP: LEER, E-11
    2. For R ACS Fail: R PACK CONT: REER, D-9 CKPT AUTO TEMP: REER, E-8
  4. If unable to restore either system, descend as required and land.

Aft Equipment Hot

images

G450 ECS Synoptic, from Eddie's aircraft.

The procedure is fine until step 1, then it goes all wrong. Remember the prime directive when it comes to abnormal procedures in any GV series airplane: CAS, synoptics, QRH — in that order.

Call for the checklist and while the other pilot is looking for it, you can have all this done. Why the rush? In the best case scenario, a blown duct, having all that hot air back there can make things very bad, very quickly. In the worst case scenario, a fire, you are going to need to get the airplane on the ground very quickly. Do do this while the other pilot gets the checklist out:

  1. Pull up the ECS/Pressurization synoptic.
  2. Is the temperature in the duct over 250°F? Yes or no you are going to proceed, but keep the temperature in mind. If it is above 400°F (both bleeds) or 500° (single bleed with wing anti-ice) it is too high and you should be getting a Bleed Air Hot, L-R CAS message.
  3. Scan the engine instruments and pick an engine. Shut the bleeds off on that engine and confirm the pressure drops to zero. If the temperature in the duct drops appreciably you probably got the right engine. If not, swap them and try the other.
  4. That probably took you a minute. Still no relief? Now look at shutting both bleeds and the emergency descent. Your cabin is probably around 6,000 feet and your cabin leak rate should be no higher than 1,000 fpm, so you've got at least three minutes before things get interesting. (They say the maximum leak rate is 1,000 fpm but I haven't found that in writing.)

Symptoms

   AFT EQUIPMENT HOT   

Analysis

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Figure: Aft equipment overheat sensors, from Illustrated Parts Catalog, §26-14-00, figure 5.

[G450 MM, §26-14, ¶3.A] The aft equipment switches are installed in the tail compartment at FS 660, near the bleed air ducting. The switches close at 250°F ±5°F. After cooling, the switches will open at 235°F ±5°F. When any of the switches close, the circuit is completed to MAUs No. 1 and No. 2. The MAUs will then generate the Aft Equipment Hot (red) message for display on the CAS. The switches are powered with 28 Vdc from the left essential dc bus through the WARN LTS PWR #2 circuit breaker.

The 250°F switches are located fairly high and forward in the aft equipment bay. The tail compartment access door spans from FS 728 to 770, so those switches (at FS 660) are forward of that. The ambient temperature of the aft equipment during flight is said to be around 70°F, just residual heat from the engine bleed air ducts. If you have a AFT EQUIPMENT HOT indication, you either have a leaking bleed air duct, a fire, or a bad sensor indication.

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Figure: Bleed Air Schematic, from FlightSafety G450 Pilot Training Manual, Figure 9-1.

[G450 Quick Reference Handbook, page MA-3] Aft equipment hot: Aft equipment area temperature above 250°F. Possibility exists that high pressure duct has blown or that fire is in progress.

[G450 Aircraft Operating Manual, §2A-36-20, ¶2.A.]

  • The BACs open the seventh (7th) stage bleed valves of the engines to supply up to forty plus or minus three point five (40±3.5) psi of pressurized air that is temperature modulated to four hundred plus of minus ten degrees Fahrenheit (400°±10 F / 204.4°C).
  • Another adjustment is made by the BACs if wing anti-ice is required with only one engine operating or if a failure results in only one wing anti-ice valve functioning. In either condition an increased amount of high temperature air is required in order for one engine or wing anti-ice valve to supply sufficient heat to both wings to prevent the formation of ice. In this instance the BAC associated with the operating engine or wing anti-ice valve increases the temperature threshold of the air exiting the precooler to five hundred plus or minus ten degrees Fahrenheit (500±10°F / 260°C).

It should normally be pretty cold back there while in flight. The Aft Equipment Hot CAS message comes on at 250°F so if the message is real, you probably have a blown high pressure duct or there may be a fire. In the case of a blown duct, you need to take the pressure away. In the case of a fire, you need to land immediately.

Procedure

[G450 Airplane Flight Manual, §04-20-30]

  1. APU Air . . . OFF
  2. Affected Engine . . . ATTEMPT TO IDENTIFY
  3. Note: High Turbine Gas Temperature (TGT) or Fuel Flow (FF) indications, low Engine Pressure Ratio (EPR) indication, or an abnormally low BLEED AIR indication may aid in identifying the engine affected with the Aft Equipment Hot message.

  4. Affected ENG BLEED AIR . . . OFF
  5. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

    This isn't always the case, later G450s have removed the check valve that prevents bleed air coming from outside the engine to reach the cowl anti-ice. This isn't documented (yet).

    For more about this, see: G450 Cowl Anti-Ice System.

  6. Affected ECS PACK . . . OFF
  7. ISOLATION Valve . . . CHECK CLOSED
  8. IF MESSAGE PERSISTS OR RETURNS:

  9. Emergency Descent . . . COMMENCE
  10. Do you want to subject the airplane to this stress if there is an unknown problem with a hot bleed air duct back there? The cabin leak rate is said to the around 1,000 feet per minute so you should have at least 4 minutes to get down to a suitable altitude. If you are at 45,000 feet, an emergency descent is probably in order. If you are at 15,000 feet? No so much.

  11. Opposite ENG BLEED AIR . . . OFF
  12. NOTE: This will result in loss of cabin pressurization. Cabin altitude will climb at the cabin leak rate.

  13. Passenger Oxygen Masks . . . DEPLOY (IF REQUIRED)
  14. Airplane . . . PROCEED TO NEAREST SUITABLE AIRPORT AND LAND

BAS Fail

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Figure: G450 bleed air controllers, from FlightSafety G450 Maintenance Training Manual, figure 36-7.

The Bleed Air Controllers are just computers and sometimes all computers need a good reboot. I think I would just start the entire procedure with step 5 and try the circuit breakers.

images

G450 ECS Synoptic, from Eddie's aircraft.

Symptoms

BAS Fail, L-R

The ECS synoptics page may reflect unusual bleed air system behavior, particularly amber dashed lines where a temperature or pressure should be reported.

Most of the pressures and temperatures on the ECS/Pressurization page come from the bleed air controller, but the bleed air valve position does not.

Analysis

[G450 Quick Reference Handbook, page MB-19] Indicated bleed air system has failed.

Procedure

[G450 Airplane Flight Manual, §03-21-20]

  1. ECS / Pressurization Synoptic Page . . . SELECT
  2. If a single (L BAS OR R BAS) failure occurs:
  3. Affected Engine BLEED AIR . . . OFF
  4. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

    If available bleed air pressure is greater than 25 psi, the flight crew may elect to perform Steps 3 and 4.
  5. Isolation Valve . . . OPEN
  6. Two (2) ECS PACK Operation . . . MONITOR ON ECS / PRESS SYNOPTIC PAGE
  7. If available bleed air pressure is less than 25 psi:
  8. Affected ECS Pack . . . OFF
  9. Isolation Valve . . . CLOSE
  10. BLEED AIR CONT / WING ANTI-ICE CBs . . . CYCLE
  11. If time permits and system is needed for continued safe flight and landing, for L BAS Fail pull and reset at the same time L BLEED AIR CONT and L WING ANTI-ICE circuit breakers. For R BAS Fail pull and reset at the same time R BLEED AIR CONT and R WING ANTI-ICE circuit breakers.

    L BAS Fail
    • L BLEED AIR CONT: LEER, E-10
    • L WING ANTI-ICE: LEER, D-4
    R BAS Fail
    • R BLEED AIR CONT: REER, E-9
    • R WING ANTI-ICE: REER, D-13
    If both (L BAS and R BAS) failures occur:
  12. Pressurization . . . CHECK
  13. L and R Wing Anti-Ice . . . OFF
  14. If unable to maintain cabin pressure:
  15. Oxygen Masks / Regulators . . . DON / 100%
  16. Emergency Descent (if necessary) . . . COMMENCE
  17. Passenger Oxygen Masks . . . DEPLOY MANUALLY

Bleed Air Hot

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Figure: Bleed air hot indications, from FlightSafety G450 Maintenance Training Manual, Figure 36-47.

As it true with all of these pneumatic abnormals: If it is hot or failed, turn it off.

(This procedure is identical to the Bleed Pressure High scenario.)

The temperature of the bleed air outboard of the pylon should be around 570°F but will certainly not be more than the TGT of the engine itself. You don't want this hot air entering the aircraft fuselage.

The bleed air valve is on the engine itself, outboard of the pylon. If turning it off solves your problem, there shouldn't be an issue operating both packs with the isolation valve open. If the bleed switch fails to close, pulling the circuit breaker should allow it to fail close.

If you cannot get the valve to close, remember that at idle the engine cannot meet the 400°F target and the bleed air hot message should extinguish. If it doesn't, you have either a faulty temperature sensor or a series of failures from either the 7th or 12th stage valves, check valves, bleed pressure and regulating valve, precooler and precooler valves. Turning on the onside wing anti-ice and seeing how its temperature does with the engine at idle can verify hot bleed air or a faulty sensor.

Symptoms

Bleed Air Hot, L-R

The ECS synoptics page should reflect the elevated temperature.

Analysis

images

Figure: Pylon bleed air components, from FlightSafety G450 Maintenance Training Manual, figure 36-5.

[G450 Quick Reference Handbook, page MB-21] The bleed air temperature exceeds limits.

This isn't telling you what you really need to know, for that . . .

[G450 Aircraft Operating Manual, §2A-36-20; ¶3.B.] In addition to the color changes in bleed system indications on the synoptic and system pages, the MWS will generate CAS messages when the following thresholds are exceeded:

  • Precooler inlet temperature exceeds seven hundred thirty-five degrees Fahrenheit plus or minus ten degrees (T >735°F±10° / 390.5°C±5.6)
  • Precooler outlet temperature exceeds five hundred fifty degrees Fahrenheit plus or minus ten degrees (T >550°F±10° / 288°C±5.6)

Crew Alerting System (CAS) Messages:

  • Area Monitored: Precooler Inlet / Outlet Temperature
  • CAS Message: Bleed Air Hot, L-R

The issue is the temperature of the air into and out of the precooler.

[G450 Maintenance Manual §36-14-00, ¶3.A.] The fan air valve is a pylon mounted, spring-loaded open, pneumatically actuated, modulating and shut-off type valve. It is used to control the flow of engine fan air through the precooler to limit the temperature of the air in the bleed air manifold to no more than 520°F (271.11°C) over the entire aircraft operating envelope. Included are minimum miscellaneous bleed flows to the maximum of one pack plus two wings and miscellaneous bleed flows. Temperature at the precooler outlet is controlled to 400 ±10°F (204.44 ±5.55°C) in normal operating condition with wing anti-ice off or with wing anti-ice and both engine bleed air on within the engine capacity. Precooler outlet temperature is controlled to 500 ±10°F (260 ±5.55°C) during single bleed operation with one wing anti-ice on or with one wing anti-ice on and the other wing anti-ice off within engine capacity.

The air coming out of the engine bleeds is often hotter than 500°F and gets cooled to a target of 400°F under most conditions. The precooler uses engine inlet fan air to accomplish this feat so the bleed air hot condition can be caused by a failure of this engine inlet air, 7th stage air, 12 stage air, any of the valves associated with any of these air sources, or the problem could be a faulty indication. You don't want this air entering the fuselage so your normal course of action is to shut if off.

Procedure

[G450 Airplane Flight Manual §03-21-30]

  1. Affected Engine BLEED AIR . . . OFF
  2. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

    You should see indications of the valve closing on the synoptic: a pressure and temperature drop as well as movement of the valve. If you don't see these indications, your problem isn't going to get better. Pulling the bleed air circuit breaker should cause the valve to fail closed. If this doesn't work, pulling the throttle to idle should do the trick. The air leaving the engines at idle is seldom more than 300°F. Earlier Gulfstreams would have you shut down the engine at this point.

  3. Associated ECS PACK . . . OFF
  4. ECS / Pressurization Synoptic Page . . . SELECT
  5. WHEN MESSAGE EXTINGUISHES AND IF AT LEAST 25 PSI IS AVAILABLE FROM OPERATING BLEED AIR SYSTEM, TWO PACK OPERATION MAY BE ESTABLISHED IF DESIRED:
  6. Isolation Valve . .. OPEN
  7. Two (2) PACK Operation . . . ESTABLISH / MONITOR
  8. If available bleed air pressure is less than 25 psi, or single pack operation is desired:
  9. Affected ECS PACK . . . OFF
  10. Isolation Valve . . . CLOSED

Bleed Air Hot

images

Figure: Bleed air hot indications, from FlightSafety G450 Maintenance Training Manual, Figure 36-47.

As it true with all of these pneumatic abnormals: If it is hot or failed, turn it off.

(This procedure is identical to the Bleed Pressure High scenario.)

The temperature of the bleed air outboard of the pylon should be around 570°F but will certainly not be more than the TGT of the engine itself. You don't want this hot air entering the aircraft fuselage.

The bleed air valve is on the engine itself, outboard of the pylon. If turning it off solves your problem, there shouldn't be an issue operating both packs with the isolation valve open. If the bleed switch fails to close, pulling the circuit breaker should allow it to fail close.

If you cannot get the valve to close, remember that at idle the engine cannot meet the 400°F target and the bleed air hot message should extinguish. If it doesn't, you have either a faulty temperature sensor or a series of failures from either the 7th or 12th stage valves, check valves, bleed pressure and regulating valve, precooler and precooler valves. Turning on the onside wing anti-ice and seeing how its temperature does with the engine at idle can verify hot bleed air or a faulty sensor.

Symptoms

Bleed Air Hot, L-R

The ECS synoptics page should reflect the elevated temperature.

Analysis

images

Figure: Pylon bleed air components, from FlightSafety G450 Maintenance Training Manual, figure 36-5.

[G450 Quick Reference Handbook, page MB-21] The bleed air temperature exceeds limits.

This isn't telling you what you really need to know, for that . . .

[G450 Aircraft Operating Manual, §2A-36-20; ¶3.B.] In addition to the color changes in bleed system indications on the synoptic and system pages, the MWS will generate CAS messages when the following thresholds are exceeded:

  • Precooler inlet temperature exceeds seven hundred thirty-five degrees Fahrenheit plus or minus ten degrees (T >735°F±10° / 390.5°C±5.6)
  • Precooler outlet temperature exceeds five hundred fifty degrees Fahrenheit plus or minus ten degrees (T >550°F±10° / 288°C±5.6)

Crew Alerting System (CAS) Messages:

  • Area Monitored: Precooler Inlet / Outlet Temperature
  • CAS Message: Bleed Air Hot, L-R

The issue is the temperature of the air into and out of the precooler.

[G450 Maintenance Manual §36-14-00, ¶3.A.] The fan air valve is a pylon mounted, spring-loaded open, pneumatically actuated, modulating and shut-off type valve. It is used to control the flow of engine fan air through the precooler to limit the temperature of the air in the bleed air manifold to no more than 520°F (271.11°C) over the entire aircraft operating envelope. Included are minimum miscellaneous bleed flows to the maximum of one pack plus two wings and miscellaneous bleed flows. Temperature at the precooler outlet is controlled to 400 ±10°F (204.44 ±5.55°C) in normal operating condition with wing anti-ice off or with wing anti-ice and both engine bleed air on within the engine capacity. Precooler outlet temperature is controlled to 500 ±10°F (260 ±5.55°C) during single bleed operation with one wing anti-ice on or with one wing anti-ice on and the other wing anti-ice off within engine capacity.

The air coming out of the engine bleeds is often hotter than 500°F and gets cooled to a target of 400°F under most conditions. The precooler uses engine inlet fan air to accomplish this feat so the bleed air hot condition can be caused by a failure of this engine inlet air, 7th stage air, 12 stage air, any of the valves associated with any of these air sources, or the problem could be a faulty indication. You don't want this air entering the fuselage so your normal course of action is to shut if off.

Procedure

[G450 Airplane Flight Manual §03-21-30]

  1. Affected Engine BLEED AIR . . . OFF
  2. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

    You should see indications of the valve closing on the synoptic: a pressure and temperature drop as well as movement of the valve. If you don't see these indications, your problem isn't going to get better. Pulling the bleed air circuit breaker should cause the valve to fail closed. If this doesn't work, pulling the throttle to idle should do the trick. The air leaving the engines at idle is seldom more than 300°F. Earlier Gulfstreams would have you shut down the engine at this point.

  3. Associated ECS PACK . . . OFF
  4. ECS / Pressurization Synoptic Page . . . SELECT
  5. WHEN MESSAGE EXTINGUISHES AND IF AT LEAST 25 PSI IS AVAILABLE FROM OPERATING BLEED AIR SYSTEM, TWO PACK OPERATION MAY BE ESTABLISHED IF DESIRED:
  6. Isolation Valve . .. OPEN
  7. Two (2) PACK Operation . . . ESTABLISH / MONITOR
  8. If available bleed air pressure is less than 25 psi, or single pack operation is desired:
  9. Affected ECS PACK . . . OFF
  10. Isolation Valve . . . CLOSED

Bleed Pressure Low

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Figure: ECS synoptics 2/3 bleed pressure low, from FlightSafety G450 Maintenance Training Manual, figure 36-37.

The checklist asks you to make two very big determinations but doesn't give you much help on how to make those decisions: do you have a bleed air leak and should you shut down the engine? I would add a third question: do you have a bad pressure sensor?

The AFM procedure doesn't tell you any of this, it just leaves the decisions in your hands. Here is what I would do:

  1. Note the bleed pressure on both sides of the isolation valve while slowly retarding the affected side's engine power lever.
    • If the affected side pressure indication does not change, you may have a faulty sensor.
    • If the affected side pressure does change, the sensor is probably working.
  2. Close the affected side bleed valve.
    • If the bleed pressure was above zero it should drop to zero. If it doesn't, vary that side's power lever. If the pressure follows power lever movement, your bleed valve has failed to close. Pulling the circuit breaker should allow the valve to fail closed. If you can't get the valve to close you will have to shut down the engine.
    • If the bleed pressure did not drop to zero and does not follow power lever movement, you probably have a bad sensor.
  3. If the bleed valve closed successfully, open the isolation valve for a few seconds.
    • If the unaffected side's pressure drops, immediately close the isolation valve; the leak is inboard of the bleed valve. You shouldn't have to shut down the engine as long as the bleed valve remains closed.
    • If the unaffected side's pressure remains steady and the affected side's pressure rises to confirm this, the sensor is good and you either have a leak outboard of the bleed valve or a problem with the bleed air controller. Since you can't troubleshoot the BAC you should suspect a leak and should shut down the engine.
    • If the unaffected side's pressure remains steady and the affected side's pressure does not change, you have a bad sensor. You shouldn't have to shut down the engine.

Symptoms

Bleed Pressure Low, L-R

The ECS synoptics page should reflect the decreased pressure.

Analysis

images

Figure: Bleed pressure low synoptic, from FlightSafety G450 Maintenance Training Manual, figure 36-37.

[G450 Quick Reference Handbook, page MB-21] The bleed pressure is below 5 psi.

[G450 Aircraft Operating Manual 2A-36-20, ¶2.A.]

  • The BACs open the seventh (7th) stage bleed valves of the engines to supply up to forty plus or minus three point five (40±3.5) psi of pressurized air that is temperature modulated to four hundred plus of minus ten degrees Fahrenheit (400°±10 F / 204.4°C).
  • Pressure modulation is accomplished by the BACs using readings from the pressure sensors in the supply manifold to control the regulator / shutoff valve located upstream of the precooler in the supply manifold. In normal flight conditions, only (7th) stage air is required for systems operation. However, if (7th) stage pressure falls below fifteen (15) psi, the (12th) stage bleed valve will open to provide at least fifteen (15) psi.
  • If the engines are operating at low power settings as during descents or when the aircraft is at low speeds when in a holding pattern, the pressure and temperature of the seventh (7th) stage bleed air may not be sufficient to satisfy demand. The bleed air controller senses the descent mode by monitoring engine N1, altitude and Static Air Temperature (SAT). Under these conditions the BACs will supplement seventh (7th) stage bleed air if the manifold pressure drops below twenty-six (26) psi with air extracted from the twelfth (12th) stage of the engine compressor that is hotter and at a higher pressure.
  • Although both engines and are normally used to provide bleed air to both air conditioning packs for cabin pressurization and temperature control, a single engine can provide sufficient airflow to operate both air conditioning packs provided the engine power setting is high enough that a bleed air pressure of at least thirty (30) psi is maintained.
  • However, if a malfunction results in only one air conditioning pack available for pressurization and temperature control, the BAC for the engine associated with the operating pack changes the setting the regulating / shutoff valve to provide bleed air of at least thirty-five (35) psi by opening both bleed valves if needed.

So how low is too low? You should never see less than:

  • 15 psi during low power conditions
  • 26 psi in a descent mode
  • 30 psi when single-engine
  • 35 psi when only a single pack is available
images

Figure: Bleed manifold pressure sensor, from G450 Maintenance Manual, §36-21-01, figure 401.

The AFM procedure provides a procedure "if a bleed air leak is suspected" but doesn't offer any trouble shooting hints to determine if there is a leak. The AFM also recommends you shut down the engine "if necessary."

We can better analyze the cause of the low pressure and the need to shut down the engine if we understand where the pressure is measured. The bleed air manifold is divided in three places: two bleed pressure regulating and shutoff valves and one isolation valve. Each bleed pressure regulating valve is located on its engine.

The pressure sensors are located inside the aft equipment compartment, well inboard of the engine itself. The pressure on the synoptic page is inboard of the engine bleed valve but outboard of the isolation valve.

Procedure

[G450 Airplane Flight Manual, §3-21-50]

    If a bleed air leak is suspected:
  1. Affected Engine / ECS Readings . . . OBSERVE
  2. Affected Engine BLEED AIR . . . OFF
  3. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

  4. Associated ECS PACK . . . OFF
  5. Isolation Valve . . CLOSED
  6. Affected Engine Instruments . . . MONITOR
  7. If necessary:
  8. Affected Engine . . SHUT DOWN
  9. If a bleed air leak is NOT suspected:
  10. Affected Power Lever . . ADVANCE
  11. ECS / Pressurization Synoptic Page . . . SELECT

Bleed Pressure High

images

Figure: ECS synoptics 2/3 bleed pressure high, from FlightSafety G450 Maintenance Training Manual, figure 36-36.

As is true with all of these pneumatic abnormals: If it is hot or failed, turn it off. (This procedure is identical to the Bleed Air Hot scenario.) The AFM procedure is fine except that it assumes the bleed air switch will shut off the high pressure air flow. What if it doesn't?

The pressure should be around 40 psi. You don't want pressure higher than this entering the aircraft fuselage.

The bleed air switch is on the engine itself, outboard of the pylon. If turning it off solves your problem, there shouldn't be a problem operating both packs with the isolation valve open. If the bleed switch fails to close, pulling the circuit breaker should allow it to fail close.

If you cannot get the valve to close, remember that at idle the engine does not normally meet the 40 psi target and the bleed pressure high message should extinguish. If it doesn't, you have either a faulty pressure sensor or a series of failures from either the 7th or 12th stage valves, check valves, bleed pressure and regulating valve, precooler and precooler valves.

Symptoms

Bleed Pressure High, L-R

The ECS synoptics page should reflect the elevated pressure.

Analysis

images

Figure: Bleed manifold pressure sensor, from G450 Maintenance Manual, §36-21-01, figure 401.

[G450 Quick Reference Handbook, page MB-21] The bleed pressure exceeds 75 psi.

[G450 Aircraft Operating Manual 2A-36-20, ¶2.A.]

  • The BACs open the seventh (7th) stage bleed valves of the engines to supply up to forty plus or minus three point five (40±3.5) psi of pressurized air that is temperature modulated to four hundred plus of minus ten degrees Fahrenheit (400°±10 F / 204.4°C).
  • Pressure modulation is accomplished by the BACs using readings from the pressure sensors in the supply manifold to control the regulator / shutoff valve located upstream of the precooler in the supply manifold. In normal flight conditions, only (7th) stage air is required for systems operation. However, if (7th) stage pressure falls below fifteen (15) psi, the (12th) stage bleed valve will open to provide at least fifteen (15) psi.
  • If the engines are operating at low power settings as during descents or when the aircraft is at low speeds when in a holding pattern, the pressure and temperature of the seventh (7th) stage bleed air may not be sufficient to satisfy demand. The bleed air controller senses the descent mode by monitoring engine N1, altitude and Static Air Temperature (SAT). Under these conditions the BACs will supplement seventh (7th) stage bleed air if the manifold pressure drops below twenty-six (26) psi with air extracted from the twelfth (12th) stage of the engine compressor that is hotter and at a higher pressure.
  • Although both engines and are normally used to provide bleed air to both air conditioning packs for cabin pressurization and temperature control, a single engine can provide sufficient airflow to operate both air conditioning packs provided the engine power setting is high enough that a bleed air pressure of at least thirty (30) psi is maintained.
  • However, if a malfunction results in only one air conditioning pack available for pressurization and temperature control, the BAC for the engine associated with the operating pack changes the setting the regulating / shutoff valve to provide bleed air of at least thirty-five (35) psi by opening both bleed valves if needed.

So how high is too high? You should never see more than 40 psi. There are two pressure switches right next to each other separated by the isolation valve. If the pressure indicates high and the bleed switch does not work, you might try this:

  1. Bring the associated side's power lever to idle, the engine rarely achieves 40 psi at idle. If the pressure still reads above 40 psi you either have a bad pressure sensor or a series of failed valves.
  2. If the pressure did not change after you brought the power lever to idle, you should suspect the sensor. To verify the sensor is bad you can momentarily open the isolation valve to see if the opposite pressure sensor agrees. If the opposite sensor does not indicate high pressure, try bringing the retarded power lever back to its original setting and evaluate the pressure performance.
  3. If the pressure did change with power lever movement, you might indeed have high bleed pressure and you should consider shutting the engine down.

Procedure

[G450 Airplane Flight Manual, §03-21-40]

  1. Affected Engine BLEED AIR . . . OFF
  2. CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

    Verify the valve closed and the pressure has dropped. If it doesn't, see the notes above.

  3. Associated ECS PACK . . . OFF
  4. ECS / Pressurization Synoptic Page . . . SELECT
  5. If message extinguishes and at least 25 psi is available from operating bleed air system, two pack operation may be established (if desired) as follows:
  6. Isolation Valve . .. OPEN
  7. Two (2) PACK Operation . . . ESTABLISH / MONITOR
  8. If available bleed air pressure is less than 25 psi, or single pack operation is desired:
  9. Affected ECS PACK . . . OFF
  10. Isolation Valve . . . CLOSED

Cabin Pressure High

The risk here is having the CPRV all of a sudden let go and ending up with an Emergency Descent. If the pressure is high and still climbing, going to SEMI may instantly make things better. If that doesn't work, then raise the cabin altitude on the Cabin Pressure Selector Panel. If that doesn't work, consider MANUAL mode and opening the TROV a bit, but that is likely to give you another set of problems. Unless you are oceanic, your next move might be an immediate, but controlled descent. If you are oceanic you can try MANUAL, but remember to be gentle with the TROV.

Symptoms

CABIN DIFFERENTIAL 9.94

CABIN DIFFERENTIAL 9.74

You should be able to verify the pressure on the cabin pressure indicator panel:

images

Figure: Cabin pressure indicator panel, from G450 Aircraft Operating Manual, §2A-21-00, figure 10.

Analysis

[G450 Aircraft Operating Manual §2A-21-30, ¶2.H.] The CPRV is located under the lower shelf of the REER, adjacent to the TROV. It prevents excessive positive or negative pressures from damaging the airplane fuselage, doors and window and associated seals. The CPRV provides:

  • Positive differential pressure relief at 9.74 to 10.15 psi
  • Negative differential pressure relief at -0.25 psi
  • Additional outflow capability during ground operations (in AUTO mode only)

[G450 Airplane Flight Manual §1-21-10] Maximum cabin pressure differential permitted is 9.94 psi.

You may have a problem with a cabin pressure controller, the TROV, the CPRV, or a combination of any of those. You need to reset or take the problem out of the equation and end up with as much of a normal system as possible.

Procedure

CABIN DIFFERENTIAL 9.94

[G450 Quick Reference Handbook, page MA-4]

  1. Select SEMI-AUTO mode
  2. Raise cabin altitude
  3. Increase cabin rate of climb if required

CABIN DIFFERENTIAL 9.74

[G450 Quick Reference Handbook, page MB-21]

  1. In AUTO pressurization control mode, maintain level flight or decrease climb rate.
  2. Or:

  3. Switch to Semi-Automatic (SEMI) or MANUAL pressurization control mode, if required, raise cabin altitude or increase cabin rate of climb.

Cabin Pressure Low

We practice the Emergency Descent every six months but that is in a contrived atmosphere looking for a set outcome. I've had this happen to me once, at 35,000', and it was nothing like any sim scenario. Some thoughts:

  • Get on oxygen but don't make a big production out of it — just getting the mask to your face puts you ahead of the game so you can start to deal with the rest of the problem.
  • Let the Emergency Descent Mode of the autopilot handle flying the airplane, you can bring the throttles to idle once the nose is pointed down to help things along.
  • Get the pax on oxygen.
  • Let everyone below you know that's where you are headed.
  • RAM Air? That's going to shut off the air conditioning packs and could make things worse. If you've got low cabin pressure chances are air flow will be the least of your problems.

Symptoms

images

Figure: Cabin pressure indicator panel, from G450 Aircraft Operating Manual, §2A-21-00, figure 10.

CABIN PRESSURE LOW

You may have the classic Rapid Depressurization scenario with a loud pop, a rush of cold air, and the air fogging instantly. Or you might just have the CAS message which you should be able to verify the pressure on the cabin pressure indicator panel.

Analysis

images

Photo: ECS synoptic, from Eddie's aircraft.

Remember that pressurization occurs because the engines pump air into the vessel and the TROV lets it out in a metered, controlled way. If you lost pressurization there is either not enough air coming in or too much is getting out.

You may have lost a structural component of the fuselage, a window, or a seal. Or it might just be a problem with a cabin pressure controller, the TROV, the CPRV, or a combination of any of those.

Procedures

[G450 Quick Reference Handbook, page EH-3]

If cabin pressurization is lost, proceed as follows:

  1. Crew Oxygen Masks . . . DON
  2. Emergency Descent Procedure / Checklist . . . COMMENCE
  3. See Emergency Descent Procedure, page EH-3

  4. Passenger Oxygen Masks . . . MANUALLY DEPLOY
  5. Passenger Oxygen Masks . . . VERIFY DEPLOYMENT
  6. Pressurization . . . RESTORE
  7. If unable to restore cabin pressurization:

  8. RAM Air . . . SELECT ON TO PROVIDE CABIN AIRFLOW
  9. NOTE: See Loss of Automatic Pressurization Control, page EH-5.

Cool Turbine Hot

images

Figure: G450 Air Conditioning Flow Schematic, from FlightSafety International G450 Pilot Training Manual, figure 21-2.

There is a little bit of thermodynamics involved here but it isn't too tough if you follow the flow of air in the diagram above from the pack inlet valve to the compressor outlet temp sensor:

  1. The hot air (400 to 500°F) from the engine bleeds enters the air conditioning pack through the pack inlet valve.
  2. The air is cooled by the primary heat exchanger, a brownish color on the diagram.
  3. That air is compressed to increase its pressure which has the side effect of reheating it prior to going into the secondary heat exhanger.

Why reheat the air right after you've cooled it? It has to do with the ability to extract even more heat from it after it is run through the secondary heat exchanger and eventually when it is expanded in the air cycle machine. What is important to note here is that if the air is allowed to get much hotter than where it started, the heat exchanger itself loses effectiveness. So we have a temperature sensor after the compressor and before the primary heat exchanger.

The fix is to simply shut the pack off and if you have two packs with the same problem, descend and shut both down.

Symptoms

Cool Turbine Hot, L-R

You might see indications of a problem on the ECS/Pressurization Synoptic or with temperature control.

Analysis

images

Figure: Compressor outlet temperature sensor, from FlightSafety G450 Maintenance Training Manual, figure 21-15.

[G450 Aircraft Operating Manual, §2A-21-20, ¶1.]

  • Scrubbed bleed air enters the ACP, first passing over the primary stage of an air to air heat exchanger. The heat exchanger uses ambient air drawn into a ram air scoop in the dorsal fin as a cool air source to initially reduce bleed air temperature. On the ground, ambient air is drawn into the air scoop by a fan powered by the rotation of the ACP turbine (described in the following section). In flight, with high ram air pressure available from increased airspeed, most of the ram air in the inlet bypasses the fan. The ambient cooling air is exhausted through louvers in the lower tail section of the airplane.
  • After initial cooling the bleed air is routed to the compressor side of the ACP. Compressor rotation is powered by the turbine side of the ACP. Both the compressor and the inlet duct fan share a common shaft with the turbine section. The spinning motion of the compressor approximately doubles the pressure of the incoming air (in order to drive the turbine side of the ACP) and also warms the air.
  • Some of this warm air (compressor outlet air is limited to 450°F) is ducted to the turbine side of the ACP to prevent icing in the water extraction operation of the condenser and also is used to maintain a minimum air temperature at the inlet to the ACP turbine. Most of the warmer, pressurized air is ducted through a secondary heat exchanger in the ram air duct for recooling.
  • The air then is directed to impinge on the blades of the turbine section of the ACP, spinning the turbine blades and powering both the compressor side and the inlet duct fan. The energy dissipated in rotating the ACP turbine results in further cooling of the pressurized air.

If cooling turbine discharge air above 450°F is allowed into the secondary heat exchanger, which is upstream of the primary heat exchanger, the primary heat exchanger will lose efficiency. The problem can "feed on itself," getting hotter and hotter. No doubt about it, the pack is going to have to be shut down. It takes electricity to do that, since the pack inlet valve fails open.

Procedures

[G450 Airplane Flight Manual, §03-01-30]

    CAUTION: IF BOTH L Cool Turbine Hot AND R Cool Turbine Hot MESSAGES ILLUMINATE, DON CREW O2 MASKS AND DEPLOY PASSENGER O2 MASKS. START AN EMERGENCY DESCENT IMMEDIATELY TO 15,000 FEET OR MEA, WHICHEVER IS HIGHER, BEFORE SELECTING BOTH PACKS OFF.

  1. Associated (L or R) PACK . . . OFF
  2. Operational Pack Bleed Source Pressure . . . VERIFY COMPENSATION TO 35 ±3 PSI
  3. The bleed pressure targets 40 psi maximum at high engine power settings but normally sits at something above 15 psi when in low power situations, 26 psi in a descent, or 30 psi if single-engine. Switching a pack off tells the bleed air controllers to ramp this up to 35 psi.

    When message extinguishes:
  4. Associated (L or R) PACK . . . ON
  5. Both (L and R) PACKS . . . SELECT WARMER TEMPERATURE
  6. If message recurs:
  7. Associated (L or R) PACK . . . OFF
  8. Operational Pack Bleed Source Pressure...VERIFY COMPENSATION TO 35 ±3 PSI

CPCS Low Air Flow

images

Figure: Air flow control system schematic, from G450 Wiring Diagram Manual, §21-20-00, figure 1, sheet 1.

This is an odd procedure and there isn't much documentation about what actually triggers the CPCS Low Airflow CAS message. The best I could do was the wiring diagram which refers to a flow switch on the pack inlet valve (highlighted in red above) which wants at least 25 ppm. The QRH gives you three possible reasons but the procedures don't make any sense given those reasons.

By all means pull out the QRH but this is a problem you need to think through, following the QRH blindly can make things worse.

Symptoms

CPCS Low Airflow

You probably won't notice this until you get the CAS, then on the synoptic you may notice problems with one or both air conditioning packs. The cabin altitude may be climbing.

Analysis

[G450 Quick Reference Handbook, page MB-24] Causes:

  1. The Cabin Pressure Control System (CPCS) less airflow than required, or
  2. The outflow valve is fully closed, or
  3. One or both pack inlet valves have failed.

Procedure

[G450 Quick Reference Handbook, page MB-24]

  1. Increase thrust, if able.
  2. Select L-R Wing Anti-ice to ON.
  3. Select ECS/Pressure synoptic page.
  4. Monitor pack outlets and temperatures (34 - 36°F).
  5. If unable to maintain or control cabin altitude, execute an Emergency Descent procedure.

Technique

images

Figure: Cabin altitude vs. aircraft altitude vs. differential pressure, from G450 Airplane Flight Manual, page 5.1-16.

It appears the low air flow is reported at the pack inlet valve. But even if this isn't true and you take the three suggest causes listed in the QRH (and the G450 Airplane Flight Manual, page 3A-17), a better course of action may be as follows:

  1. Select ECS/Pressure synoptic page.
  2. If the outflow valve is fully closed or if cabin altitude is lower than scheduled on the chart shown, switch the pressurization system to SEMI and select the scheduled cabin altitude as a way of increasing air flow.
  3. If there is no output from a single air conditioning pack and it appears its pack inlet valve is closed even though the switch is on, try turning that pack switch off. The logic of the system should compensate the operating pack inlet bleed pressure to 35 psi.
  4. If there is no output from both air conditioning packs and it appears the pack inlet valves are closed even though the switches are on, try pulling one or both pack inlet valve circuit breakers (marked as "L PACK CONT" D-10 on the LEER and "R PACK CONT" D-9 on the REER), these valves fail open without electrical power.

If all that fails you can always go back to the QRH procedure.

EER Hot

images

Figure: Overheat detection system diagram, from G450 Aircraft Operating Manual, §2A-26-00, figure 6.

These overheat switches are typically set at 150°F. Gulfstream is starting to purge the books of these numbers but it still exists for EER Hot and PDB Overheat. Why do I harp on this? Because 150°F isn't that much.

Dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESS LOW message is usually set a 8,000' and exceeding it could cause an automatic Emergency Descent.

Symptoms

BAGGAGE EER HOT

EER HOT

PDB OVERHEAT, L-R

Analysis

images

Figure: Equipment overheat switch, from G450 Maintenance Manual, §26-14-01, figure 405.

[G450 Maintenance Manual, §26-14-00, ¶3.A.]

  • The LEER switches are installed on several of the shelves in the LEER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135°F ±5°F. When any of the switches close, the circuit is completed to MAU No. 1. The MAU will then generate the L EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the left essential dc bus through the WARN LTS PWR #2 circuit breaker.
  • The REER switches are installed on several of the shelves in the REER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135°F ±5°F. When any of the switches close, the circuit is completed to MAU No. 2. The MAU will then generate the R EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the right essential dc bus through the WARN LTS PWR #1 circuit breaker.
  • The baggage compartment EER switches are installed in the baggage compartment EER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135° ±5°F. When any of the switches close, the circuit is completed to MAU No. 1. The MAU will then generate the Baggage EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the right essential dc bus through the WARN LTS PWR #1 circuit breaker.
  • There is no reference to PDB overheat switches other than in the GV and G550 manuals that speak of the PDB overheat occuring over 175°F.

The electronic equipment racks are normally cooled with conditioned air and dedicated fans, they shouldn't be too much hotter than the cabin temperature. Increasing the flow of cool air by lowering cabin temperature and increasing air flow and the prescribed solutions. Even if it does cure your overheat, you still need to consider the cause of the overheat. You might have more problems ahead of you.

Procedure

[G450 Airplane Flight Manual, §3-20-20]

  1. EER Fan(s) Circuit Breakers . . . CHECK
  2. NOTE: For Baggage EER Hot message, inspect compartment loading to ensure that airflow to the electronic equipment is not blocked by luggage or other items.

  3. COCKPIT, FWD CABIN and AFT CABIN Temperature Controls . . . SELECT MANUAL, FULL COLD
  4. If message persists:
  5. Pressurization Control . . . SEMI
  6. Cabin Altitude . . . INCREASE TO 7,900 FT
  7. Raising cabin altitude increases airflow through the TROV

    For EER Overheat message:
  8. Altitude . . . DESCEND TO 33,000 FEET OR BELOW
  9. Descending to 33,000 feet or below causes the EER fans to shift to high speed, thereby increasing cooling airflow.

    This also kicks the fans cooling the TRU's into low speed mode. If the issue is high draw from a component, you might consider closely monitoring TRU loads to anticipate a TRU overheat.

  10. EER Cover Panels . . . REMOVE AND CHECK FOR HOT COMPONENTS
  11. For Hot Component(s) . . . PULL COMPONENT POWER CIRCUIT BREAKER(S)
  12. For PDB Overheat message:
  13. PDB Cover Panel . . . CHECK FOR POPPED CIRCUIT BREAKERS
  14. CAUTION: DO NOT RESET ANY POPPED CIRCUIT BREAKERS.

    If PDB Overheat message persists:

  15. Nearest Suitable Airport . . . LAND

Loss of Automatic Pressurization Control

images

Photo: Cabin pressure selector panel, from Eddie's aircraft.

This procedure assumes either your cabin pressure control panel is broken or both cabin pressure controller channels have failed and you are in danger of over pressurizing the fuselage. If you can't get control using MANUAL, the book wants you to turn both packs off and execute an emergency descent.

This might be your best course of action, no doubt about it. But what if you are half way across the pond on top of a bunch of tracks and still have a long way to go? You might be taking a controllable situation and creating an uncontrollable mess. There is another way, but it is just my technique. You might consider adding it to your bag of tricks.

Symptoms

CPCS Control Panel Fail

CPCS Fail-Select Manual

If you are in level flight the only symptom may be on the CAS. If climbing or descending, the pressurization system might behave erratically.

Analysis

images

Figure: Pressurization system block diagram, from G450 Maintenance Manual, §21-31-00, figure 1.

[G450 Aircraft Operating Manual, §2A-21-30, ¶2.C.] The CABIN PRESSURE CONTROL panel on the cockpit overhead provides push-button switches and a rotary (spring-loaded neutral) knob for pressurization mode selection and manual control (see Figure 8). An indicator of TROV shutter position is also furnished. The push-button switches are illuminated to indicate the active pressurization mode. The FAULT portion of the FAULT / MANUAL push-button also serves as an indication of AUTO and SEMI mode failure. Selections on the panel enable the flight crew to perform and control the following functions:

  • Select the AUTO, SEMI or MANUAL mode of operation.
  • Select the FLIGHT or LANDING mode of operation.
  • Manually position TROV shutters to open or close, or to any intermediate position.
  • Monitor the rate of TROV shutter movement.

If the CAS says the CPCS control panel has failed you still use the panel to select manual. If the CAS says CPCS Fail-Select Manual, it is saying both channels have failed and again you select manual. Either case leads you to a checklist that tries to get control back using SEMI.

Procedure

CPCS Control Panel Fail

[G450 Quick Reference Handbook, page MB-23]

  • Cause: CABIN PRESSURE CONTROL panel has failed.
  • Corrective Action: Select FAULT/MANUAL switch to MANUAL, Control cabin pressurization with manual (MAN HOLD) knob, go to page EH-5

CPCS Fail-Select Manual

[G450 Quick Reference Handbook, page MB-23]

  • Cause: Both CPCS channels are failed.
  • Corrective Action: Select FAULT/MANUAL switch to MANUAL, Control cabin pressurization with manual (MAN HOLD) knob, go to page EH-5

[G450 Quick Reference Handbook, page EH-5]

  1. FAULT / MANUAL . . . MANUAL
  2. MAN HOLD . . . CONTROL TO ±500 FPM RATE OF CHANGE
  3. FAULT / MANUAL Switch . . . DESELECT MANUAL
  4. AUTO / SEMI . . . SEMI
  5. Cabin Pressure Selector Panel . . . SET VALUES AS REQUIRED
  6. Remember you are resetting a computer and it could very well be the simple act of deselecting/re-selecting could get the system back.

    If semi-automatic pressurization control is not regained:
  7. FAULT / MANUAL . . . MANUAL
  8. CAUTION: WHEN OPERATING IN MANUAL MODE, MONITOR CABIN ALTITUDE CLOSELY, ESPECIALLY IN DESCENT, TO ENSURE THAT CABIN ALTITUDE DOES NOT DECREASE TO LESS THAN LANDING FIELD ELEVATION. CARE MUST BE TAKEN TO LAND UNPRESSURIZED WITH THE OUTFLOW VALVE IN FULL OPEN POSITION.

  9. MAN HOLD . . . CONTROL TO ±500 FPM RATE OF CHANGE
  10. CAUTION: CLOSELY MONITOR CABIN DIFFERENTIAL PRESSURE. DO NOT ALLOW IT TO EXCEED 9.74 PSID.

    NOTE: When operating in the MANUAL mode, the rate of change should be monitored to maintain a maximum of 500 feet per minute UP or 500 feet per minute DOWN. Care should also be taken to land unpressurized with the outflow valve indicator in full OPEN position.

    If manual pressurization control is not successful, and if cabin differential pressure will exceed 9.74 PSID:
  11. RAM AIR Switch . . . RAM
  12. NOTE: Selecting RAM will shut off bleed air for pressurization and the airplane will depressurize.

    Selecting RAM has the effect of turning both packs off. You might consider this instead:

    1. Turn one pack off.
    2. Decrease thrust on the engine driving the operating pack to control pressure within limits.
  13. Crew Oxygen Masks . . . DON
  14. Altitude . . . DESCEND TO SAFE ALTITUDE (25,000 FT OR BELOW)
  15. Passenger Oxygen Masks . . . MANUALLY DEPLOY
  16. Upon reaching a safe altitude, attempt to regain control of the pressurization system as follows:
  17. RAM AIR Switch . . . OFF
  18. AUTO or MANUAL Control . . . ATTEMPT TO RESTORE

TRU Hot

images

Figure: Equipment cooling fans, from G450 Aircraft Operating Manual, §2A-21-00, figure 5.

A Forward Floor or TRU Hot message usually portends future electrical problems that might be fixable by non-electrical means. It doesn't take much to cause a TRU Hot message — 150°F — dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESSURE LOW message is usually set at 8,000' cabin altitude and exceeding it could cause an automatic Emergency Descent.)

Another thing you can do is to climb above 36,000' if you are below it. That will kick the PSU fans to high speed mode.

What else can you do? You know the normal load on your TRU's rarely tops 33% and if you see one that is well above that there are two possibilities. Something on that bus has a high draw or the TRU itself is going bad. If dropping a fuel pump doesn't help, try pulling the circuit breaker for the TRU, you know the load will automatically go to the AUX TRU so what have you got to lose?

Symptoms

You may see some degradation of the TRU's performance on the DC Synoptic, or it may have dropped off line. Of course you should also get a CAS message:

AUX TRU HOT

ESSENTIAL TRU HOT

MAIN TRU HOT

Forward Floor Area Hot

You may have been sent here via the:

35K Altitude Trip Fail

Analysis

images

Figure: G4350 TRU location, from FlightSafety G450 Maintenance Training Manual, figure 24-25.

[G450 Airplane Flight Manual, page 03-123] Aux TRU Hot — AUX TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-131] Essential TRU Hot — Indicated Essential TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-140] Main TRU Hot — Indicated TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-134] Forward Floor Area Hot — Forward underfloor area temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, §03-20-10] Cooling air is drawn from the Left and Right Electronic Equipment Rack (LEER) and (REER), aided by the exhaust of the Passenger Service Unit (PSU) fan and routed beneath the forward floor area primarily to cool the five Transformer-Rectifier Units (TRUs): Auxiliary (AUX), Left Essential (L ESS), Right Essential (R ESS), Left Main (L MN) and Right Main (R MN). The amber Forward Floor Area Hot message is displayed on the Crew Advisory System (CAS) when the temperature under the forward cabin floor between the EERs exceeds 150°F. It is likely that an overheat underneath the forward floor area is associated with an overheating Transformer/Rectifier Unit (TRU) and will be accompanied by one of the TRU Hot CAS messages.

The TRU's are located under the forward floor, just inboard of the main entrance door. Any of these messages means one or more of the TRUs may be overheating. The trip point of these switches are not very high, only 150°F. Getting cool, conditioned air over the TRUs may solve what ails you.

[G450 Airplane Flight Manual, page 03-148] 35K Altitude Trip Fail — Relay fails to enable 35,000 feet switchover. EER cooling fans stay in high speed mode while PSU fan stays in low speed mode.

[G450 Maintenance Manual, §21-25-00, ¶3.]

  • The fans in the Left Electronic Equipment Rack (LEER) and Right Electronic Equipment Rack (REER) are located on the bottom shelf of each rack and pull air down through the racks. The LEER fan exhausts to the Transformer Rectifier Units (TRUs) below the REER, then overboard through the thrust recovery outflow valve. The REER Fan exhausts under the floor and across the aircraft to the outflow valve. The fans come on when power is applied to the L MAIN 28 Vdc bus, if the circuit breakers in the LEER circuit breaker panel labeled L/R EER FAN are closed.
  • The Personal Services Unit (PSU) fan, located under the entrance way, pulls air from the PSU and exhausts it under the floor, aft of the FS 169 bulkhead. This air cools the center TRUs and exhausts overboard through the thrust recovery outflow valve.

[G450 Maintenance Manual, §21-25-00, ¶4.]

  • The LEER and REER fans have two speeds which are controlled by applying a ground to the logic pins. Each fan changes from a fast speed to a slower speed at 35,000 feet altitude. The air conditioning units energize two relays to ground the required pins to change the speed of the fans. These relays are energized by the air conditioning control units. Only one air conditioning control unit has to be operating for the fans to change speed.
  • The PSU fan is a two speed fan. It runs at a low speed until either of the environmental control system relays are energized at 35,000 feet and then shifts into high speed. The PSU fan is powered by the left main 28 Vdc bus and comes on when power is applied and when the circuit breaker labeled L PSU FAN, located in the LEER circuit breaker panel, is depressed. This fan also has a Low Speed Warning Detector (LSWD) attached. The LSWD inputs a discrete GND (ground) to the CAS when the fan speed drops below a predetermined speed. The CAS then displays the L-R EER Fan Fail (blue) or L PSU Fan Fail (blue) message.

The LEER and REER fans need to be in high speed mode at low altitude while the PSU fans need the higher speed at high altitudes. If either of these fans fail to go into high speed when called for, you might next see a TRU overheat.

Procedure

[G450 Airplane Flight Manual, § 03-20-10]

If a "Forward Floor Area Hot" or one of the TRU Hot messages is displayed while on the ground:
  1. FAULT / MANUAL Switch ... MANUAL
  2. MAN HOLD Knob ... FULL OPEN
  3. All Zone Temperatures ... MANUAL / FULL COLD
If message(s) does not clear within two minutes and TRU loads are normal, shut down airplane and investigate.
If a "Forward Floor Area Hot" or one of the TRU Hot messages is displayed while in flight:
  1. L PSU FAN Circuit Breaker ... CHECK IN
  2. FWD CABIN and AFT CABIN Temperature Zones ... MANUAL / FULL COLD
  3. Pressurization Control Mode ... SEMI / INCREASE CABIN ALTITUDE TO 7,900 FT
  4. Raising cabin altitude increases airflow through the TROV.

  5. Pressurization Control Mode ... AUTO
  6. DC Power Synoptic Page ... SELECT
  7. TRU Load(s) ... CHECK
  8. If any TRU load is excessive:

    What is excessive? We usually see our TRU's in the high twenties, sometimes low thirties. I've never seen a G450 TRU above 38%.

  9. Load (On Bus That TRU Supplies) ... REDUCE
    • If a main TRU is high, consider turning off corresponding alternate fuel boost pump.
    • If an essential TRU load is high, consider turning off corresponding main fuel boost pump.
    • If the AUX TRU load is high, consider turning off the fuel boost pump associated with the Main or Essential DC Bus that the TRU is powering.

    CAUTION: ENSURE THE CROSSFLOW VALVE IS OPEN BEFORE TURNING OFF BOTH BOOST PUMPS ON ONE SIDE TO PROVIDE A SOURCE OF PRESSURIZED FUEL TO THE ENGINE.

    If message(s) persists:
  10. Circuit Breaker (For Overheating TRU) ... PULL
  11. If electrical system integrity must be preserved or if Forward Floor Area Hot message persists:
  12. Pressurization Control Mode ... SEMI / INCREASE CABIN ALTITUDE TO 7,900 FT

You should not set the cabin pressure above 8,000 feet since that will trip the CABIN PRESSURE LOW warning and could cause an automatic emergency descent.

Uncontrollable Zone Temperature

The Air Conditioning Controller does a marvelous job regulating the temperature of each zone but it is a computer. The Left ACC receives its power through the L PACK and CAB AUTO TEMP circuit breakers. The Right ACC receives its power through the R RACK and CKPT AUTO TEMP circuit breakers. Pulling and resetting these reboots the ACC.

There's always manual. Remember that rotary knob gives you 60°F to 90°F control in AUTO but a lot more in MANUAL. How much more? Well as cold as the pack can get (35°F) and as hot as it gets before you get a duct overheard (215°F). Be careful.

Symptoms

Select Manual Temp, C-F-A

You may have an undesired temperature in the (C)ockpit, (F)orward cabin, or (A)ft cabin.

Analysis

This may just be an Air Conditioning Controller having an electrical tantrum or something between channels that just needs to be reset. It could also be a sensor problem or something within the air conditioning system itself.

Procedures

[G450 Airplane Flight Manual, §03-01-20]

  1. ZONE / DUCT TEMP DISPLAY Indicator . . . MONITOR
  2. NOTE: The ECS / PRESS synoptic page may also be used to monitor temperature(s).

  3. Zone Temp AUTO / MAN Switch (Associated Zone) . . . MAN
  4. Associated Temp Control Knob . . . ADJUST
  5. IF THE FAULT CORRECTS ITSELF AND TIME PERMITS, AUTOMATIC TEMPERATURE CONTROL CAN BE RESTORED AS FOLLOWS, BASED UPON CAS MESSAGE DISPLAYED, ONLY IF REQUIRED FOR CONTINUED SAFE FLIGHT AND LANDING:

  6. Affected PACK CONT / AUTO TEMP CBs . . . SIMULTANEOUSLY PULL AND RESET

References

* FSI G450 PTM, FlightSafety International Gulfstream G450 Pilot Training Manual, Volume 2, Aircraft Systems, October 2008

* FSI G450 MTM, FlightSafety International Gulfstream G450 Maintenance Training Manual, August 2008

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Airplane Flight Manual, Revision 36, December 5, 2013

Gulfstream G450 Illustrated Parts Catalog, Revision 17, October 31, 2012

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013

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Revision: 20120101
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