Gulfstream II


S t u d y    G u i d e

Systems  &  Limitations  Overview

    The following is an overview of the basic systems on the Gulfstream II. It does not address the winglets that may be installed.  They give the airplane about 20 minutes more endurance and cost about half a million dollars.  Other than including some limitations, I did not discuss the tip tank airplanes because they are just too ugly and were made obsolete by the G II-B; a G II with a G III wing.
    It is not intended to provide enough information for you to build the airplane. It is intended to provide general information for familiarization and review.  This guide addresses only the G II.  The G II-B has it's own study guide on this web site.   For the latest and most accurate information, refer to the  current AFM.  Many flight manuals on older airplanes, if subjected to inspection, will be found to be out of date.  Guess who gets the shaft if there is a problem, and you were operating with out of date information.  Look in the nearest mirror and see!


Gulfstream II

Wing Span
68' 10"
Tailplane Span
Gear Track / Center Axle
13' 8"
Overall Length
79' 11"
33' 4"
24' 6"
Turn Radius / Wheel to opposite Tip
Gear axle to opposite Elevator
Gear axle to Nose
Nosewheel Steering Angle
78.5 deg L & R


ASC 81
ASC 256
Tip Tank
Max Ramp 
58,000 lbs
60,000 lbs
62,500 lbs
65,300 lbs
66,000 lbs
Max Takeoff
57,500 lbs
59,500 lbs
62,000 lbs
64,800 lbs
65,500 lbs 
Max Landing
51,430 lbs
55,000 lbs
58,500 lbs
58,500 lbs
58,500 lbs 
Max Zero Fuel
38,000 lbs
39,000 lbs
42,000 lbs
42,000 lbs
42,000 lbs 

    The above weights are maximum certificated limits.  The actual maximum weights for a particular flight may vary due to the performance limitations.  If the aircraft can not meet the required "Takeoff Field Length" and "Climb" limitations, (engine out climb performance), the maximum takeoff and/or landing weights are reduced such that the requirements are met.  See the performance charts in the AFM for details.


Vmo / Mmo
      With ASC 200
Vsb / Msb
     With ASC 200
367 kts / 0.85 Mach 
300 kts SL / 338 kts @ 28,100 ft
338 kts / 0.85 Mach
300 kts / 0.85 Mach
     With ASC 200
     With ASC 200
213 kts
160 kts
275 kts / 0.75 Mach
257 kts / 0.75 Mach
Vfe      10 Deg 
            20 Deg 
            39 Deg
250 kts / 0.60 Mach
220 kts 
170 kts
Emergency Ext.
225 kts / 0.70 Mach
250 kts / 0.70 Mach
175 kts
 89 kts
102 kts
Mach Trim Inop
20,000 MSL / 0.75 Mach

Holding Speeds

Non Icing Conditions
200 kts
Icing Conditions
180 kts / 10 deg Flap

    Note:  More exact holding speeds may be derived from the aircraft's performance documentation, however, there will not be a whole lot of difference unless your weight is greater than 46,000 lbs.  The 200 knot figure is a legal holding speed at any altitude.  Above 46,000 lbs. add about 2 knots per thousand pounds additional weight.  If you need to hold at a speed higher than 200 kts, and don't have the AIM handy, just request your desired holding speed with ATC.  Any speed ATC approves is legal, just ask.  Holding fuel flow at 46,000 lbs varies from about 3,800 lbs / hour at sea level to 2,900 lbs / hour at 15,000 ft.  At heavier weight, add about 50 lbs / hour per 1,000 lbs above 46,000 lbs.

Recommended Minimum Maneuvering Speeds

Recommended / Minimum
Flaps Up
200 kts / 170 kts
Flaps 10 deg
180 kts / 160 kts
Flaps 20 deg
160 kts / 150 kts
Flaps 39 deg
Vref + 10 kts

These speeds should keep you out of trouble if you keep the bank angle under 30 degrees.  Cross check the Angle of Attack Indicator.  Keep it in the green!

Altitudes & Misc.

Max Alt T.O. & LDG
     With Supplement G-II-79-19
  10,000 ft 
 13,360 ft
Max Enroute Altitude / ASC 299
Max Altitude  Flap & Gear
45,000 ft
43,000 ft
20,000 ft
Min Temp T.O. & LDG 
Max Slush 
Max Water
-40 Deg C
0.75 inch
0.50 inch
Max Temperature 
Abv 10,000 ft
ISA + 35 C 
ISA +30 C
Min Temp SL - 3,500
-40 C
 3,500 - 5000 Linear
-40 C to -35 C
5,000 - 10,000
-35 C
10,000 - 35,000 Linear
-35 C to -70 C
Above 35,000
-70 C
Max Demonstrated X-Wind
20 kts
Max Runway Slope
Max Tailwind Component T.O. & LDG
10 kts
Load Factor Limit 
    Flaps Up 
    Flaps Extended 
2.50 G
2.00 G

Turn Clearance Limits

Gulfstream II
41.0 Feet
47.5 Feet
45.0 Feet
Taxiway for 180 deg Turn
52.0 Feet

Spey Mk 511-8  Engine Limitations

 570 C
106.6 %
100,1 %
585 C
5 Minutes
Max Continuous
106.6 %
98.1 %
No Limit
Rec Max Climb
94.5 %
490 C
No Limit
Rec Max Cruise
94.0 %
470 C
No Limit
Min / Full Bleeds
64.0 %
Max Reverse
92.2 / 91.7 % *
490 C
30 Sec
Max Overspeed
103.1 %
20 Sec
Max Overtemp
610/615 C **
20 Sec
Max Acceleration
595 C
2 Min
Ground Idle
52.0 - 55.5 %
540 C
*  SN # 1 thru 82  and 775 with ASC 41 & 83 and higher except 775
**  With SB 77-43
Note:  Above 30,000 ft, it is possible to exceed the engine RPM limits and still be below the max TGT.  The N2 is the one to watch!

   Engine Oil System Limitations

Min /  @ Max Continuous
40 psi
Min / Idle
15 psi
Min To Complete Flight @ Max Cont. 
35 psi
Min To Complete Flight @ 92% N2
30 psi
Min To Complete Flight @ 84% N2
25 psi
Min To Complete Flight @ 52% N2
13 psi
Max Oil Temp
+100 C
Max Transient Oil Temp / 15 Min
120 C
Min Oil Temp for Start 
Min Oil Temp Above Idle
-40 C
-30 C

Flight Controls

     The flight controls on the G2 are cable driven with hydraulic boost.  They are powered by both the "Combined" and "Flight" hydraulic systems.  Each of the systems provides 1500 psi to the flight control servo actuators.  When the landing gear or flaps are extended, the combined system pressure increases to 3,000 psi.  If one system fails, the remaining system pressure increases to 3000 psi.  Failure of one hydraulic system therefore, does not result in a loss of control effectiveness.


    The hydraulically boosted ailerons provide roll control.  Either or both hydraulic systems will power the ailerons.  They are assisted by the flight spoilers.  A bungee connects the spoiler mixer and aileron on each side so that the ailerons and spoilers can be moved regardless of the status of the the other.   Roll trim is provided by a trim tab located on the left aileron.  The aileron trim tab is set with a manual trim wheel in the cockpit.  No electric stuff here!


    The Gulfstream II is equipped with a moveable stabilizer, elevator, and elevator trim tab system.  The elevator is hydraulically boosted by both hydraulic systems..  Elevator trim adjustments are made with the manual trim wheel in the cockpit, or electrically from the control yoke.  The stabilizer is automatically adjusted when the flap setting is changed in order to compensate for changes in trim caused by flap extension and retraction.    The stabilizer is moved via a gearbox in the tail.  The flap gearbox is connected to the gearbox in the tail.  The stabilizer position is indicated by a gauge within the flap position indicator.  If the stabilizer does not position itself properly with each change in flap setting, return to the previous setting and go  to the checklist.  The aircraft may be landed safely with the stabilizer out of trim, however, much higher than normal control forces may be required, as the trim will not be as effective.


     The rudder, like the rest of the flight controls on the Gulfstream, is hydraulic.  Rudder trim is provided by redefining the neutral position with the rudder trim wheel in the cockpit.  The maximum rudder travel is 22 deg each side of center.  The rudder may be trimmed 10 units, or 7.5 deg either side of center.  The yaw damper is a full time system, powered by the "Flight" hydraulic system.  It has 3 deg of authority each side of wherever the trim and pilot input would place the rudder.  If the "Flight" hydraulic system fails, the yaw damper is inop.
    The rudder on the G2B is equipped with a single and a dual load limiter system.  These systems limit the forces applied to the rudder in order to avoid structural failure of the tail at high speeds.  This single rudder load limiter system limits hydraulic pressure to a maximum of 2650 pounds to the rudder actuator to avoid excessive loads on the aircraft at high speeds.  The dual load limiter system further limits the pressure to 2250 pounds.  If only one of these two systems is operable, and you have an MEL for the aircraft, you can fly.   The rudder load limiter systems have two indicator lights, an amber one for the single rudder load limiter system, and a green one for the dual rudder load limiter.  Before start, the amber light should be on.  Only after both engines are running, the amber light will  go out, indicating that the single rudder load limiter system is working.   When the combined and flight hydraulic systems are operating, the dual rudder load limiter may be checked.  This is done by slowly depressing one rudder pedal to the floor, and looking for a green light to illuminate at full rudder deflection.  Now press the other rudder pedal to the floor, and the green light should illuminate again, indicating that the rudder has reached it's mechanical stop, and the dual rudder load limiter is in fact limiting the pressure.  If you get the green light in one direction but not the other, check the rudder trim and verify that it is centered.  If not, center it and repeat the test.


    The flap system is hydraulic.  Flaps may be extended to 10 deg, 20 deg, and 39 deg with the normal system.  The alternate flap control system can be used to extend or retract the flaps to any setting between 0 deg and 39 deg.  The flaps may be operated by "Combined", "Utility", or "Aux" hydraulic systems.  When the flaps are moved, the horizontal stabilizer is repositioned via a gearbox depicted below.

Flap / Stab Gearbox
Flap / Stab Gauge

     Because it changes the angle of incidence of the horizontal stab, it minimizes trim changes during flap extension and retraction.  Flap asymmetry protection is provided via electrical signals from the outboard flap jackscrews.  The flaps system will stop if there is 1/4 inch or more difference in the linear travel of the flap actuators.  A torque limiter prevents damage to the system in the event of a jammed mechanism or an attempted extension at excessive airspeed.  A flap assymetrey will not reset until it is fixed.  If flap movement is arrested, it is either loss of hydraulics, flap assymetry, or torsque limiting.  If it was torque limiting, slow the airplane down to within the limiting speed for the flap setting you tried to get.  Retract the flaps to the previous setting, then re-extend at the proper airspeed.  If this restores flap operation, it was in fact the torque limiting system just doing it's job.  The airplane flies just fine if you stay clean until around 200 knots.  Extending the flaps at less than the limiting speeds will minimize the unwanted pitch activity during flap extension.
    In the event of unwanted flap movement, the flaps may be stopped, and the flap selector disabled by a switch on the copilot's lower arm ledge.  With this switch activated, the flaps are moved by the emergency flap control.  Any setting between zero and full may be selected.  You still have flap asymmetry protection in the emergency mode.

Max Flap Extension Speeds

10 deg
250 kts
20 deg
220 kts
39 deg
170 kts

Flight Spoilers

    All G2's and G3's have six spoiler panels, three on each wing.  All G II's,  the first eleven G II-B's and G III's  # 386, 389, and # 384 and earlier have what is referred to as the "Four Panel System".   This addresses the fact that on the "4 panel" airplanes, the inner two panels only extend when ground spoilers are deployed.  The outer 4 panels extend when speedbrakes are selected, and all extend in the ground spoiler mode .  The speedbrake system uses the outer two panels on each wing.  They may be extended to 43 deg with the speedbrake handle.  In a turn, the spoilers on the lower wing will extend to 55 degrees in conjunction with full aileron deflection.   All of the "4 panel" airplanes have a "Ground Spoiler Deact Handle" on the center pedistal in the cockpit.  The Flight Spoilers / Speedbrakes are powered by both the "Combined" and "Flight" hydraulic systems.  Speedbrakes  may be extended with up to 20 deg of flaps. Spoiler / Speedbrakes may not be deployed in flight with the flaps more than 20 deg, or with the Landing Gear extended.  The Flight Spoilers also assist in roll control, as they operate selectively with the ailerons.  A bunge allows aileron movement in the event the spoiler is stuck.

Ground  Spoilers

    The "Ground Spoiler" system extends the inboard spoilers to 55 degrees.  At the same time, it extends the speedbrakes to 55 degrees as well.  This is done only when both nutcracker switches are in the ground mode, both thrust levers are at ground idle (hard stops), and the ground spoiler switch is armed.    The ground spoilers may not be armed without a successful nutcracker test after gear extension.

Four Panel  Speedbrake Systems

4 Panel System
Max Aileron, 0 Speedbrake
2 Low Wing Spoilers 43 deg
0 Aileron, Max Speedbrake
4 Flight Spoilers 43 deg
Max Aileron, Max Speedbrake
2 Low Wing Spoilers 55 deg 
Up wing 43 deg
Auto Ground Spoilers
All Panels 55 deg

Nosewheel Steering

        Ground steering is provided by a hydraulically actuated steerable nosewheel.  The nosewheel may be steered 82 degrees each side of center. The nose steering is powered by the "Combined" or the "Utility" hydraulic systems.  In the event those systems are inop, differential braking may be used for directional control on the ground.   In order to use differential braking to steer, you must turn the nosewheel steering system off.  This is done with a red guarded switch located just forward of the tiller.  The nose steering system is disabled unless the nut crackers are in the ground position.  Loss of Main DC Bus power has the same result as turning the nosewheel steering system off.

    If on landing, the "No Ground Spoiler" light is illuminated after touchdown, the pilot not flying shall announce it, deploy the flight spoilers, and remind the pilot flying that the nosewheel steering system will be inop.  This is because one or both of the nutcrackers remained in the flight mode after touchdown.  One nut cracker switch is sufficient to tell the airplane that it is in the air, but both are required to enable the ground spoiler and associated ground systems.


     The normal braking system provides braking to all of the main gear wheels.  The main wheel rotation is arrested during gear retraction.  The combined hydraulic system provides 250 pounds of hydraulic pressure to the brakes during the gear retraction cycle.  An anti-skid system provides skid protection during braking with the normal system.  This includes protection if the brakes are applied prior to touchdown.  The anti-skid system requires Main DC Bus power.  The parking / emergency brake is powered by an accumulator.  Use of the emergency brake system usually blows the tires, as it is almost impossible to modulate, and locks the main wheels.


     Gulfstream II SN # 1 thru 238 (except 220) were delivered with the Sperry SP-50G autopilot.   The SPZ-800 autopilot was installed on # 239 and later.  In this guide, we will address the SP-50G.  The SPZ 800 will be discussed in the G III study guide. The SP 50-G is the older of the two systems, and was a commonly installed in the Boeing 727-100, and earlier 727-200 airplanes.  It is a great system  even today,  It can even be certified for MNPS and RVSM if the appropriate mods are done the the aircraft..  It provided all of the basic autopilot functions such as wing leveling, heading hold, NAV and will intercept and fly an ILS approach if properly set up by the crew.  Altitude preselect is an option, but should be found on most G II-B's.  Do not engage "Manual Glideslope" unless you are within a quarter of a dot of on glidepath.  Although it is not a limitation,  if you are more than half a dot away from dead center on the glide path  it will capture, but you and your passengers may not like that portion of the ride.  Avoid the same mistake on your next job!  Manual Glideslope is normally used to capture the glideslope from above.  If you are intercepting from below, AutoGS is a much better idea.
    Unlike many of the crude autopilots of it's day, the SP-50 works well in the IAS and Mach speed modes.  It does, however, lack a half bank mode.  It is a bit on the aggressive side when capturing a new course at a waypoint change.  For passenger comfort, switching to heading mode until established on the new course is better.  The SP-50G is not integrated with the flight director system.

SP-50G Autopilot

SP-50G Autopilot Limitations

Do not operate the SP-50G Autopilot:
Above Vmo/Mmo
Below 1.2 Vs
Below 38,000 lbs and aft of 43% MAC CG
With Yaw Damper Inop
Above 35,000 ft with an engine inop.
With Autotrim inop
During coupled approaches with an engine inop
During takeoff or landing
Do not SELECT  Manual Glideslope below 1,000 ft AGL

    Although it is not a limitation, it is highly recommended that you not select Manual Glideslope if you are more than half a dot away from dead center on the glide path.  It will capture, but you and your passengers may not like that portion of the ride.  Manual Glideslope is normally used to capture the glideslope from above.  If you are intercepting from below, Auto is a much better idea.


    All of the Gulfstream II and III aircraft are powered by two Spey Mk 511-8 engines.  These engines are rated at 11,400 pounds of thrust each.  The Spey Mk 511-8 is a twin spool axial flow Jet Engine.  The LP compressor, (N1 or Fan)  is a 5 stage compressor.  Some of the air from this LP compressor is routed around the engine core, and provides thrust.  The rest of the LP air is ingested into the HP or N2 compressor.  The N2 section has 12 compressor stages.  Behind the compressor sections is the combustion chamber, then the HP turbine, and finally the LP turbine.  The HP and LP turbines drive their respective compressor sections.

Percent vs RPM

N1 / LP  100%
8,393 rpm
N2 / HP 100%
12,484 rpm

    Accessories mounted on the engine include oil pumps, high pressure fuel pump, a hydraulic pump as well as alternator and generator for each engine.  These are driven by the HP or N2 section.  The engine oil is cooled by fuel via a fuel / oil heat exchanger.  It heats the fuel and cools the oil.  Oil pressure indications are provided by an AC powered gauge and a DC powered low pressure light (Idiot Light) for each engine.  There is an engine oil replenishing system installed on Gulfstream Jets.
Engine oil may be serviced only on the ground.
    Variable inlet guide vanes, and farther back, a surge bleed valve on the 7th compressor stage are installed to stabilize the engine idle, prevent compressor stalls, and optimize the engine acceleration characteristics.  A malfunction of the surge bleed system will result in unstable idle, poor acceleration, and compressor stall in many instances.

Engine Gauges

Engine Start Panel


    Vibration is monitored in the engine with the TVI or Turbine Vibration Indicator system.  This system allows the crew to monitor the engine vibration.  This can alert the crew of impending malfunction or failure of the rotating engine components.  Some vibration is normal, however a change in vibration level may indicate impending doom for the engine.  See the chart below.

TVI  Indication
Pilot  Action
Increase of 1.0 or more during steady state operation Slowly close thrust lever & observe vibration during deceleration.  Make an note of the maximum value.  If less than 3.0 (3.5 between 67% and 74% N2), restore power and monitor engine instruments.
A sudden increase of 3.0 (3.5 between 67% and 74% N2) Perform engine shutdown if situation permits.  Monitor engine warning systems.
During start, Increase of 3.0 or more. Abort the start.
During shutdown, Increase of 3.0 or more. Record incident and have engine inspected.

Fuel Heat

    An automatic Fuel Heating system is installed on these engines.  This is to prevent any ice formation in the engine fuel system.  The fuel is heated by P3 bleed air, and monitored by fuel temperature gauges in the cockpit.  These gauges are powered by the essential DC bus.  Some fuel heating does result from the fact that the hydraulic systems have heat exchangers in the hopper tanks, however the intent of these is to cool the hydraulic fluid.  The fact that the fuel is heated a small amount is not important.

Top Temp Control

    A temperature control and limiting system is installed on the Spey 511 Mk-8 engine.  This system, if on, will prevent a TGT overtemp.  The temp control amplifier is powered by the 115 Volt AC instrument Inverter Bus.  The Top Temperature Control System is to be ON except in the event the system fails.

APU / GTCP 36-6
G II & G II-B 

Note:  All APU's installed in G II's, G II-B's and G III's with the DC Electrical System are limited to ground operation only.  All G III's have the GTCP 36-100 APU, but only the AC models,  G III # 357,  # 402 & Sub except  # 875 are certified to operate in flight.  Do not think that just because you may have the GTCP 36-100 APU that you can operate it in flight.  You can't , except for the late G III's listed above.

 The great thing about the APU on the Gulfstream is that it will allow you to start the engines and go someplace, instead of just sitting on the ramp.  The APU on the G2 is for ground operation only.  It can provide air for engine start, or air conditioning, as well as AC electrical power.  Some of this AC may be converted to DC with the Emergency TR.  The DC can then power the inverters, providing constant frequency AC.  So, in a round about way, the APU can power the entire airplane on the ground.  Even with the 200 Amp TR, you have plenty of DC for the task, unless you get stupid with an excessive number of boost pumps and landing lights.  If your TR load is excessive, disconect one of the batteries for a minute or so.  Let the other battery charge, then place the remaining battery back on line.  For normal operations, you do not need the optional 300 Amp TR.  It is mostly a G III thing.

GTCP 36-6   APU Control Panel

 To start the APU, turn on the APU Master Switch.  Wait for the Low Oil Pressure light to illuminate, indicating that the APU door is open.  Press and release the start button, and wait.  When the APU RPM is stable at 100%, turn on the Alternator.  Check that both AC busses are powered, then select the Emergency TR Main & ESS.  The ESS only position is primarily for use in flight for split buss operation. Caution: Do not open the APU air valve unless the Main DC Buss is powered.  Doing so will result in a very quick overheat of the bootstrap unit, as the control for the ground cooling fan is on the Main DC Bus.  If the Main DC Bus is not powered, the ground cooling fan will not come on.
    Check that the DC Volt Meter reads 26 Volts.  The DC Emergency Feeder light should be illuminated, indicating that the emergency TR is powering the Main and Essential DC Busses.
    The APU Air must be turned on if you wish to do anything really festive, like start the engines or use the heating / air conditioning system.  Do not run the engines much above idle with the APU Air Valve Open, as this is not good for the APU.
    To shut down the APU, turn off the Air and Alternator, let the temperature stabilize, then press and release the "Overspeed" test switch.

Note:  Performing a "Nut Cracker" test with the APU running will shut it down, as the APU will think that the airplane has just become airborne.  I learned this from experience.  The bright side is that I was the only occupant of the aircraft at the time and therefore did not have to explain my mistake.  The APU is a ground only item on the G-II aircraft.  This remains true even if the dash 100 APU is installed.  The dash 100 is certificated for operation in flight on the later G III's, but not on any of the G II's.

Fire / Overheat  Protection

Engines / APU

    The engines and have continuous wire fire detection loops in the engine compartments.  When heated to their alarm value, they will cause the engine fire warning system to activate.  The respective left or right ENGINE FIRE lights will illuminate.  On # 173 & Sub and aircraft with ASC 152,  fire bell will sound.  Press the "Fire Bell Mute" button to cancel the bell.  The fire may be extinguished by pulling the respective fire handle, and discharging one or both of the engine fire bottles.  Their are two engine fire bottles, each containing 4.5 pounds of  Bromotrifluromethane and about 600 psi of nitrogen to disburse it.  Either or both bottles may be discharged into the selected engine.

G II Engine Fire Warning

    The APU fire warning is provided by a thermal switch.  The APU fire bottle is like the engine fire bottles, only smaller.  It contains 2.5 pounds of the extinguishing agent, and the 600 psi nitrogen to distribute it.  The APU fire bottle may be fired by lifting the guard and moving the switch.  Any fire bottle that is discharged must be removed from the airplane, serviced, and reinstalled.  The engine and APU fire detection systems are not part of the Master Warning System.

Note:  If you get a fire warning, and perform the appropriate procedure, test the fire detection system after you believe that the fire has been extinguished.  If the system won't test, the fire detection loop may have been damaged.  In this case, you don't really know if the fire was actually extinguished.


    Overheat warning is provided for the generators, alternators, TR's, radio rack, and inverters.  Some of the warning lights serve two items, such as a TR and an Inverter.  These require some diagnosis.  Refer to the checklist.  The E and B inverters and the B inverter's TR have an auto shutoff feature, as they are located in the radio rack inside the airplane.  When the B Inverter shuts down due to an overtemp, it also pops the breaker for the bus it was powering.  If one bus caused both it's own inverter and the B Inverter to overheat, the problem is most likely on the bus.


    Overheat warning is provided for the Flight and Combined, systems, and the Aux hydraulic pump.  These systems do not incorporate any automatic features to deal with the problem.  Consult the checklist for the appropriate procedure.


    The wings, tail compartment, bleed air manifolds, aft compartment, and bootstrap unit are equipped with overheat warnings.   On the ground, the bootstrap unit will shutdown automatically in the event it overheats.  In flight, the bootstrap unit will only give you a warning, and must be shut down by the crew.  Selecting either Emergency Pressurization or Ram Air will shut down the bootstrap unit.  Emergency pressurization air is available from the LP compressor on the right engine.  The remainder of the warnings must be handled by the crew.

Fuel System

    The G II  Fuel System is simple.  Fuel is stored in the wings.  Each wing tank has a "hopper" tank that is kept full with ejector pumps and gravity.  Four DC electric fuel pumps provide fuel pressure to the engine driven fuel pumps.  Warning lights will illuminate when the hopper tank has 675 pounds of fuel or less.  This amounts to between 20 and 25 minutes at 200 knots IAS at 5000 MSL, or about 50 miles to dry tanks..
    Two of the fuel pumps are designated as "Main", and two as "Alternate".  They are in fact identical.  They are located in the main wheel wells.  Normally, all four pumps are on.  If one pump on a given side is turned off, the other pump can supply ample pressure.  In the event that the operating pump fails, and the failed pump's switch is in the on position, the other pump on that side will come on.  The main fuel pumps are powered by the ESS DC bus.  The alternate fuel pumps get there power from the MAIN DC bus.
    You may supply fuel to either or both engines from either tank by opening the crossfeed valve and switching the fuel pumps off on the side from which you do not wish to feed.  An intertank valve is also installed, allowing fuel to gravity flow between the tanks.

Left Tank
Right Tank
11,650 Lbs
11,650 Lbs
23,300 Lbs
1,726 Gal
 1,726 Gal
3,452 Gal

Fuel System Switches

    The airplane burns about 5,000 lbs the first hour, 3,500 lbs the second hour, 3,200 lbs the third hour, then 3,000 lbs per hour thereafter.  Low altitude holding requires 4,000 lbs / hour fuel flow.  This gives you about 6 hours  range with 45 minutes worth of holding fuel.  This will take you  more than 2,400 nautical miles at normal cruise.  Use of  long range cruise will result in additional range.  These are the "No Brainer" figures.  With a little time in the airplane and a few minutes in the book, you should be able to do better.

Hydraulic System

    The Gulfstream II hydraulic system uses skydol.   It has two engine driven pumps, an electric aux pump, and a utility pump that is driven by the "Flight System".   This "Utility Pump" is a hydraulic motor, (driven by the flight system) connected to a hydraulic pump that can pressurize the "Combined System" except the flight controls in the event that the combined system pump, or the left engine were to fail.  There is no fluid transfer between the flight and combined systems.  If the failure of the combined system includes loss of the fluid, the utility pump will not have any effect, as there is nothing for it to pump!  The combined and flight hydraulic systems have heat exchangers located in their respective fuel hopper tanks in order to cool the hydraulic fluid.  These have nothing to do with the "Fuel Heat" system which is located in each engine's nacelle.

Combined System
    The "Combined System" is powered by a hydraulic pump on the left engine, or in the case of  Combined System pump, or engine failure, the Utility Pump. The utility pump is driven by the Flight System.  The electric "Aux Pump" can power 5 items only.  See the chart below.

Flight System
    The "Flight" System" is powered by an engine driven hydraulic pump located on the right engine.  It's normal operating  pressure is 1500 PSI.  It will operate at 3000 PSI if the combined system pressure drops below 800 psi.  This is to increase the pressure to the flight controls, and to enable the flight system to power the Utility Pump.

Utility Pump
    The Utility pump is a hydraulic pump that pressurizes the Combined System when it's own pump is not putting out sufficient pressure for whatever reason.  Operation of the utility pump requires at least 2,200 psi flight system pressure.   The Utility pump can drive all of the combined system items except the ailerons, elevator, rudder and flight spoilers.  In the event it is necessary to use the utility pump, those items are operated by the flight system.  If the flight system does not work, the utility pump won't work either, as the utility pump is driven by the flight system in the first place!

Aux System
    As you can see from the table below, the aux system, in normal operations, is used on the ground.  It allows you to extend and retract the landing gear doors during the preflight, closes the cabin door, and provides pressure so you can set the parking brake.  It also operates the Flaps and Brakes on the ground or in flight.

Hydraulic System Control & Indication

Combined System

Flight System
Ailerons   Ailerons
 Rudder   Rudder / Yaw Damper
 Flight Spoiler / Speedbrake   Flight Spoiler / Speedbrake
---Check Valve---
  Right Thrust Reverser
<Utilit Pump-<
Utility System Motor
Ground Spoilers <<<--- *Right Thrust Reverser
Nose Steering  <<<--- Flight Sys Reservoir Press.
Thrust Reverser(s) <<<---
Stall Barrier <<<---
Windshield Wipers <<<---
Combined Sys Reservoir Press. <<<---

<-Aux Pump
Landing Gear <<Note: Gear on ground only!
Pedal Brakes <<<---
Flaps <<<---
Parking Brake <<<---
Cabin Door (Close only) <<<---

* Aircraft 123 thru 163, 166 thru 190, 193 thru 198, and those with ASC 138.  All others have thrust reversers powered by the combined or utility hydraulic systems.

Note:  Use of the Aux Pump to operate the Landing Gear on the ground applies to the landing gear doors only.  The gear doors are opened on the ground for preflight, and to keep condensation from accumulating in the main gear doors.  If you leave the airplane in an environment where the temperature goes below freezing, any water that may be in the main gear doors can freeze, and may interfere with landing gear operation if it remains during gear retraction, or cause damage on the ground if a chunk of ice falls out and hits something.

Electrical System

   The electrical system on the Gulfstream II  may look complicated at first glance, but it is not.  It consists of 2 batteries, two 300 amp DC generators, and two variable frequency (wild AC) 115 Volt 20 KVA alternators plus an APU alternator of the same capacity.  Not counting the APU alternator, because it can't be used in flight,  the Gulfstream II and II-B have 2 DC generators and 2 Alternators.  Also they have 4 inverters. Three of these inverters make constant frequency AC from variable frequency AC by using the variable frequency ac to power the A, B, and C  Transformer / Rectifiers to make DC from AC.  This DC is now used to power the A, B, and C inverters that provide the constant frequency AC power.  The "E" Inverter produces constant frequency AC for emergency use.  It is powered by the essential DC Bus.  The bottom line is, as long as you have at least one of the four electrical generating devices operational, you will have at least the minimum electrical power needed to fly the airplane.  In the Gulfsteam, one out of four ain't bad!


    In general, the DC system powers most of the electrical components on the airplane.  The alternators provide power to heat the windshields, power some interior lighting,  and to power the TR's that produce the DC that  powers the inverters. It may sound complicated, but a peek at the electrical schematic will make it a bit less confusing.  The inverters supply the 400 hz AC that is needed by the gyros, avionics, and flight guidance system.  The "E" (instrument) inverter is powered by the ESS DC bus.  It is only needed when the Main Inv. Bus is not powered by the A or B inverter, or by the left generator tie bus through the use of the Inv Alt Pwr, or "Skip" switch.   The "A" and "C" inverters are powered by their respective TR's, but can also be powered, if desired,  by the DC system through the use of the INV ALT PWR switches.  These are also refered to as "Skip" switches.
    The Emergency TR is powered by the left alternator bus.  This bus should be powered if any one of the three alternators is operating.  The emergency TR can power the ESS DC bus, and both the MAIN and ESS DC busses as desired.  When the airplane is on the ground without the engines running, the ESS TR powers the DC system.  This is normal.

Constant Frequency AC System

    The constant frequency AC system is controlled by the switches below.  Each AC bus has it's own 3 position switch.  Normal, Off, and Standby or Emerg. are the switch positions.  With all three switches in NORM, the A inverter powers the Main and INST Inverter Busses, the C inverter powers the Secondary INV bus, and the B inverter powers nothing.  As long as the A or B inverter is powering the Main Inv. Bus, the Main and Inst AC busses can almost be considered one bus, as they are connected.  This remains so as long as either the A or B inverter is powering it.  If, however, the E inverter is powering the Emergency Instrument Bus, the relay between the two busses opens and the E inverter powers ONLY the Instrement Inverter Bus.  If the main or secondary inverter bus switch is selected to standby, the B inverter powers that particular AC Bus.  The B inverter can power the Main OR  the Secondary AC bus, never both at the same time.  If both the Main and Sec bus switches are in standby, the Main gets the power.

G II-B AC Electrical System
Generator / Alternator / Inverter / Battery Switches

GOInverter / Constant Frequency AC Bus Check


   Variable frequency AC is provided by the two ships alternators, and on the ground only, the APU alternator.  Constant frequency AC is provided by converting the variable frequency AC to DC, with a Transformer / Rectifier or "TR".  The then "TR's" DC output powers  inverters that produces the constant frequency AC.  There are four inverters in this system.  The "E" inverter can power only the Instrument AC Bus.  The "C" Inverter powers only the Secondary AC Bus.  The B inverter can power the Main, or Main and Instrument AC Busses, OR  it can power the Secondary AC Bus, but not both.  The A inverter can power the Main AC, or the Main AC and the Instrument AC busses.  The E and B inverters are in the radio rack, and have thermal protection that will shut them down if they overheat.  The A and C inverters have overheat warning lights, but no auto shutdown protection.  If the TR's feeding the A or the C inverters fail, those inverters may be powered by the DC system through the use of the "Skip" switches.  The inverters overheat warning tells you that the respective inverter or the "TR" has overheated.  Switch inverters and let things cool for a minute, then if you wish to diagnose the problem, turn the inverter back on and use the "Skip" switch.  If the fault does not recur, it was most likely the "TR", and if it does, it was the inverter that was the problem.

Emergency Gen's & Inverter Alternate Power

ASC 165 - On # 001 - 155 powers inverter control circuits from ESS DC instead of MAIN DC.
                   # 156 & sub are that way from the factory.

ASC 151 - On # 001 - 155 Installs INV ALT Power or "SKIP" switches. This enables you to power
                   the "A" inverter from the from the R GEN tie bus, or the "C" inverter from the L GEN tie bus.
                   # 156 & sub are that way from the factory.


   DC is supplied by either or both of the DC generators, and / or by the Emergency "TR". The Emergency "TR"  is powered by any one of the ships alternators through the left alternator bus.  The DC power is distributed by two busses, Essential and Main.  Loss of one DC generator is not a problem, as you merely revert to "Split Buss" operation to reduce the load on the remaining generator..  Place the TR switch to ESS, and Bat switch to Emergency.  Now, your remaining DC generator powers the main DC Bus.  The Emergency TR powers the Essential DC Bus, and keeps the batteries charged.  The Emergency TR is powered by the left AC bus.   When you select the Emergency TR, the left AC equipment bus becomes unpowered as indicated in the previous electrical schematic..  Operation of the Emergency TR is illustrated below.  With the failure of both DC generators, and at least one alternator on line, the Ess DC Bus can be powered by the Emergency TR.  You can also power the Main DC Bus, but be cautious not to overload the TR or the alternator.  The 300 amp TR is not installed on all airplanes, and the alternator is limited to 53 amps for continuous operation.

G II-B DC Electrical System

DC System Emergency Operation / TR Powers DC Busses
This is normal operation on the ground!

    The Emergency TR can power the Ess DC Bus, or both the Ess and Main DC Bus, as selected by the crew.  The 200 Amp Emergency TR needs a bit more monitoring when the batteries have been drained a bit.  Disconnecting one battery reduces the load on the TR by as much as 50 to 100 amps.

Gulfstream II  Electrical System

GO Battery Integrity / DC Systems Check

Electrical Abnormals / Examples

One Generator & One or both Alternators Operating

    Split the bus!  Battery switch to Emergency, TR switch to Essential.  ESS DC Bus is powered by the TR, and the Main Bus is powered by the remaining generator.  Load on the operating generator is reduced.  The inverters are powered normally.  All busses are powered except the AC equipment bus which is lost whenever the emergency TR is in use.  If one alternator is inop, the AC monitor buses will be unpowered as well.

One Alternator & Both Generators Operating

    No action required; The alternator busses get power from the opposite alternator bus when their own alternator fails.  The AC monitor busses will not be powered.  Monitor the alternator load.  Windshield heat is a high draw item.  In non-icing conditions, it can be shed if speed altitude and humidity permit.  One of the inverters may be powered by the DC system through the use of the "Skip" switch if AC load reductin is desired.

One Generator Operating & Both Alternators Failed

    Monitor the load on the remaining generator.  Inst. Inv. Bus is powered by the E inverter.  You will have at least the Essential DC Bus and depending on the DC load, the Main DC Bus as well.

One Alternator Operating & Both Generators Failed

    Battery switch to Emergency, TR switch Essential.  ESS DC Bus is powered by the TR.  If the load on the generator permits, the main DC bus may be powered.  The inverter system should operate normally.

Electrical Capacities

20 KVA / 53 Amps
58 Amps / Emergency
DC Generators
28  Volt / 300 Amps
DC Brushless Generators
ASC 285
28 Volt / 300 Amps
Single Gen. Operation
28 Volt / 250 Amp
Emergency TR / Standard
200 Amp
Emergency TR / Optional
300 Amp
APU Alternator
20 KVA / 53 Amp 
Batteries 1 & 2 
24 Volt / 36 Amp Hour

Ice and Rain Protection

    The Gulfstream II  is certified for flight into known or forecast icing conditions.  We will discuss the various Ice and Rain protection devices system by system.  The vertical and horizontal stabilizers do not require ice protection.  This was determined by flight testing during the aircraft's certification process.  All of the Gulfstream's anti-ice systems are powered by the Essential DC system.


    The engine inlet hub fairing, inlet guide vanes, and the nose cowl are heated by engine bleed air in order to prevent ice formation.  The air is controlled by two engine anti-ice valves located on each engine.  They are powered by Ess DC, and fail to the closed position.  These valves are opened and closed with the "ENG. ANTI-ICE" switches.  Each valve has a separate circuit.  To determine if one anti-ice valve has failed to open, compare the engine anti-ice duct pressures. The engine EPR pitot probes are heated electrically heated when engine anti-ice is selected on.  On aircraft with ASC 111, the EPR pitot probes are heated when the Pitot Heat switch is on.
    If the anti-ice duct pressures are the same at equal rpm, they are OK.  If they differ by 15 psi or so, and one is below 45 psi, one valve is probably failed closed.  If the pressure is more than 60 psi, a valve has more than likely failed open.  These valves fail to the closed position when Essential DC power is lost.

Engine & Wing Anti-Ice


    The wing leading edges are heated with engine bleed air in order to prevent ice formation.  Wing heat is controlled with two "Wing Anti Ice" switches.  Each of theses switches controls it's respective wing anti-ice valve.  This does not mean that you may heat one wing and not the other.  The bleed air ducting downstream of the wing anti-ice valves is connected by a crossover manifold such that either Wing Anti Ice switch being turned on heats both wings.
    After activating the wing anti-ice system, the wing leading edge begins to heat.  When the respective wing temperature reaches 100 deg F, the that wing's green light above the Wing Anti Ice switches will illuminate, indicating normal operation.  The temperature is automatically regulated.  If the wing anti-ice controllers fail, and the temperature reaches 180 deg F, a red L or R WING HT light will illuminate.  You must then turn one or both wing heat switches off as necessary to extinguish the warning lights.  The entire wing anti-ice system is useable during emergency DC operation, as the CB's are on the Essential DC Bus.


    Rain removal is performed with hydraulically powered windshield wipers.  The windshields are heated electrically.  When the windshield heat switch is placed in the "ON" position, the windshields receive electrical power from the "Right Alternator Bus".  This bus can be powered by either of the ships alternators, or the APU alternator if it is operating.  The AC power on the Gulfstream is 3 phase.  Without going into lots of detail, three phase alternators behave like three alternators, providing 3 wires, and an electrical ground.  The first "Phase", or "A Phase" powers the captain's windshield.  "B Phase" powers the copilot's windshield, and "Phase C" powers all the side windows as well as the "DV" window.  The front windows have temperature sensors that provide the temperature controllers with the information necessary to regulate the amount of power to the windshields, thus controlling the windshield temperature.  The front and DV windows have green annunciator lights that will advise you when the windshields are powered.  The side and DV window temperature is controlled by thermal switches.  There are no annunciator lights that address the side windows.

Pitot-Static & AOA

    The pitot tubes and the angle of attack probes are electrically heated.  The left form the ESS DC Bus, and the right from the Main DC Bus.  When engine anti-ice is on, the EPR pitot tubes are also heated if ASC 111 is installed.  Depending on the mod status of the airplane, you will have:

    On airplanes without ASC 111, the engine EPR pitot tubes are heated when the respective engine anti-ice system is selected on.



    The cabin is pressurized with HP bleed air from the N2 compressor section of each engine.  If the air-conditioning unit (boot strap) fails, emergency pressurization may be selected.  This provides air from the LP or N1 compressor section of the right engine.  The pressurization is regulated with one of two outflow valves.  The normal outflow valve is electrically operated.  It is AC powered in the "Normal" mode, and DC powered in the " manual mode.  The second outflow valve is a "Safety Valve", requiring no electrical power whatsoever.  This valve provides relief at maximum pressure differential, and vacuum relief, as well as a pressurization rate limiter.

    During normal operation, before takeoff, you set cruise altitude, barometric pressure, destination field elevation and cabin rate.  The system does the rest.  Change the barometric pressure setting if appropriate, and at top of descent, move the switch from "Flight" to "Landing"..  That's it!  If manual mode is required, move the outflow valve as necessary with the manual (DC electric) system.  Go easy, as the valve moves quite fast.  A general announcement to the passengers may keep you from looking  like a dummy!

Pressurization Control

Emergency Pressurization

    Emergency pressurization air comes from the LP bleed port on the right engine.  Selecting RAM CABIN AIR closes the air-conditioning valve, causing  the airplane to depressurize.  Once the cabin has depressurized, the ram air valve opens to ventilate the cabin.

Air Conditioning

    The same air that pressurizes the airplane also provides air conditioning and heating.  What a surprise we have here!  The engine bleed air is quite hot, up to 900 deg  F when it comes out of the HP port, and about 400 deg F once it passes through the precooler..  In order to cool it, there are heat exchangers in the engine pylons, and a "Boot Strap" unit to further cool the air.  The rest of the industry calls it an "Air Cycle Machine", "ACM" or "PAC", but Gulfstream insists on being different.    In simple terms, the hot air is cooled, compressed, cooled again, and allowed to expand, driving the cooling turbine, further reducing the temperature of the air.   This cold air is mixed with warm air to regulate the temperature.  (For more theoretical information, see the "Glossary" included in the study guide section of this web site.  See "Air Cycle Machine")  If for any reason, like maybe smoke evacuation, you wish to depressurize the airplane and ventilate it with ram air, you may do so by placing the "Cabin Air" switch to "RAM".  This closes the valve that allows bleed air to enter the cabin, and after the cabin pressure leaks down, allows ambient air to ventilate, but not pressurize the aircraft.
    Control of the temperature is managed by a selector switch and two rheostats on the overhead panel.  The switch positions are "OFF", "NORM", "CKPT RHEO" and "CABIN RHEO".  In "NORM", the system works as intended.  The cockpit thermostat regulates the temperature in the cockpit, and the cabin thermostat does the same for the cabin.  In  "CKPT RHEO" , the cockpit thermostat and rheostat regulate the temperature of the cockpit and cabin.  In "CABIN RHEO", the cabin thermostat and rheostat regulates the temperature of the cockpit and cabin.  In "OFF", the valves go to full cold.  This may be OK in Phoenix in the summer, but as for Bozeman Montana in the winter, or after about half an hour at cruise, you will freeze your boss, and he will be unable to sign your paycheck.  If you must use the "OFF" position, there are two valves in the baggage compartment that will enable you to control the temperature manually.  They are located on the left, or aft edge of the external baggage compartment door.

Temperature Control

Warning Lights

    GO  Entire Warning Light System

Note:  I will divide these up by system at a later date, but for now, here they are. If you are looking for a specific one, try CTRL  F, and type in what you want to find.

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