This guide addresses only the G III AC model.   The G III with the AC electrical system is much more like a G IV from an electrical  standpoint.  Other than electrical, the G III's are pretty much the same.  Of all the corporate aircraft I have flown, ( 23 Type Ratings )  the G II-B and G III are are my favorites.  The G III is about two and a half feet longer than the G II-B.  This amounts to about two million dollars per foot.  The G III is quieter in the cockpit due to the improvements to the windshield design over the G II's  The Falcon 2000 is hard to beat, but the Gulfstream is like a 67 Corvette  427 with dual quads and a big cam.  It goes like lightning, and creates it's own thunder.
 

Gulfstream III

    All of the AC G III's have EFIS.  The big CRT's are nice to display FMS information, but they don't make or break the flight.  The Gulfstream III is really the same as a G II-B that is a little bit longer and has  a cockpit with a modernized look  It does have  a different windshield than the G-II and G-II-B that results in a reduction in cockpit noise at high indicated airspeed.  G-III's 402 and later as well as # 357 have a different electrical system than the earlier G-II and G-III aircaft.  This is the same electrical system that wound up in the G IV.  Some like it better, some don't.  The primary differences between the "AC" or late model G-III and the "DC" or early models is the electrical system, autopilot / flight guidance system and the cockpit displays.

    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.

     The flight controls on the G III 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 airplane can be flown manually in the event both hydraulic systems fail.

Ailerons

  The hydraulically boosted ailerons provide roll control.  Either or both hydraulic systems will power the ailerons.  Roll control is enhanced  by the flight spoilers.  When one of the ailerons is deflected up, the two outboard speedbrake panels on the same wing will extend, reducing lift and increasing drag on that side.  The speedbrake panels on the side of the down aileron remain stowed.   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!

Elevator

    The Gulfstream III is equipped with a moveable stabilizer, elevator, and elevator trim tab system.  The elevator is hydraulically boosted.  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.

Rudder

  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 G III 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 psi 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 psi.  If only one of these two systems is operable, and you have an MEL for the aircraft, you can fly.   Each  rudder load limiter system has it's own indicator light, 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 the rudder trim and repeat the test.  It will most likely work the same on both sides now.

Flaps

    The flap system is controlled electrically, and operated with hydraulic power from the "Combined", "Utility", or "Aux" hydraulic systems..  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.  If the flaps do not respond to movement of the flap selector, they may be positioned by manually moving the flap control valve with the red emergency flap control handle on the panel to the right of the co-pilot's seat.  The flaps, again,  may be operated by "Combined", "Utility", or "Aux" hydraulic systems.
    There are two circuit breakers associated with the flap system.  They are the "Flap Control" and "Manual Flap Control" circuit breakers.  If the "Flap Control" breaker has popped, flaps   This is provided you do not have a flap asymmetry problem.  If the "Manual Flap Control" circuit breaker is popped, the flaps can not be moved unless the circuit breaker can be reset and no flap asymmetry exists.  The flap shutoff  valve is between the aircraft's hydraulic system and the flap motor.  If this valve is closed, the hydraulic flap motor will not move the flaps.  For this valve to be open, DC power must be applied to the valve through the "Manual Flap Control" circuit breaker, and no flap asymmetry can exist, as the flap asymmetry system removes power from the hydraulic valve regardless of the status of any circuit breaker.
Asymmetry
    Flap asymmetry protection is provided via electrical signals from the asymmetry switches attached to 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.  The asymmetry switches are attached to the left and the right outboard flap actuators.  If a flap asymmetry exists, the flap control relay will open, removing power from the "Flap Shutoff Valve" regardless of the status of any other part of the system.
Torque Limiting
    A torque limiter prevents damage to the system in the event of a jammed mechanism or an attempted extension at excessive airspeed.  You can, however, damage the flaps by accelerating to an excessive airspeed after the flaps are already extended.  Because they are mechanically extended by hydraulically driven jackscrews, they do not retract prior to structural failure.  A flap asymmetry will not reset until it is fixed.  If flap movement is arrested, it is either loss of hydraulics, flap asymmetry, or torque 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.

When the flaps are moved, the stabilizer is repositioned via a gearbox depicted below.
 

      Because the system changes the angle of incidence of the horizontal stab, it minimizes trim changes during flap extension and retraction.

Flight Spoilers

    All G II's and G III's have six spoiler panels on the wing.  They are referred to as 4 and 6 panel systems.  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 "6 panel" airplanes use all of the spoiler panels in flight, but only extend them to 26 deg as opposed to the 43 deg deployment on the 4 panel system.  In a turn, the spoilers on the lower wing will extend to 55 degrees in conjunction with full aileron deflection.  Gulfstream III,s # 300 thru 384, and # 386 & 389 have the four panel system.  These airplanes are equipped with the Ground spoiler deact handle.  Numbers # 385 and higher, except 386 and 389 have the 6 panel system, and thus do not have the ground spoiler deact handle.   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 uses the same spoiler panels as the flight spoilers.  It merely extends them to 55 degrees, instead of the 26 degrees the speedbrake handle will give you.  aileron and speedbrake together may result in 55 degrees deflection of the outer two panels on the wing on the down side of the roll command.
    The ground spoilers should not be armed without a successful nutcracker test after landing gear extension.  There is an easy way to figure out if you have a four or six panel airplane. All "AC" G-III's are six panel airplanes.   They do not have a ground spoiler deact handle.  By serial number, the six panel airplanes are:   G III # 385, 387, 388, and 390 and subsequent as well as any G III incorporating ASC 50.  I don't know about # 357.  If you deal with this airplane, just look to see if there is a ground spoiler deact handle.  If there is, it is a 4, not a 6 panel airplane.  With the 6 panel airplanes, the inboard 2 panels extend with speedbrake application, but not in conjunction with aileron deflection.  The six panel system uses the inboard panels for speedbrake and ground spoiler deployment only.

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.

Brakes

      The normal braking system provides braking with 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 in order to stop main wheel rotation.  An anti-skid system provides skid protection during braking with the normal system.  This includes protection if the brakes are applied prior to touchdown.  Anti-skid does, however, require 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.

Autopilot

   The SPZ-800 autopilot was installed on all of the G III's, as well as G II # 220 and  # 239 and later.  The SPZ 800 is an integrated Auto-Pilot / Flight Director, or Flight Guidance System.  The Sperry auto pilots are pretty good units if you look at the SP 50's and the SPZ 500 or 550 series and later.  I have, however, always wondered why Sperry insists on placing the glideslope indicator on the wrong side of it's ADI and HSI units.  A word of warning:  Do not blindly follow a flight guidance system without applying common sense.  Situational awareness is your responsibility.  Remember, these machines usually do what you tell them, not necessarily what you want them to do.   I sat and watched one fellow descend to 400 feet AGL 20 miles outside the Outer Marker on an ILS approach.  His excuse was that the flight director made him do it.  It was he, however, who programmed it.  Things like that don't only happen to stupid people.  A good pilot having a bad day or not paying attention can suffer the same fate.  This guy was lucky that his actions resulted in nothing more than a failed checkride.
    "Why did it do that?" is something most pilots have said from time to time.  Most auto pilot errors are due to flawed programing by the crew, but not all of them.  Use the bells and whistles, but keep one eye on the raw data just to make sure.  Paranoia is only sound thinking when the world is truly conspiring against you.
 

    All of the Gulfstream II and III aircraft are powered by two Spey Mk 511-8 engines.  These engines produce 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.

    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.
 

TVI

    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.
 

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.
 

    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 G III / AC model can provide electrical power in flight, and both bleed air and electrical power on the ground.  It can provide air for engine start, or air conditioning, as well as AC electrical power.  Some of this AC is converted to DC with the Emergency TR to power the DC system on the ground, or in flight.  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.  If you have the 300 Amp TR, you have plenty of  DC for the task, unless you get stupid with an excessive number of boost pumps and landing lights.  The 200 Amp TR is more than enough if you monitor the amp gauge, and temporarily disconnect one battery during the initial charging after APU start.  You may not need to do this very often, but be aware.
 

    To start the APU, make sure the battery switches are on.  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 theAUX Power Switch   If things are working normally, the batteries should be showing +38 Amps each, and all the AC and DC Busses should be powered.
    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.
 
 

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.
 

    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.

Electrical

    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.

Hydraulic

    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.

Pneumatic

    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.
 
 

    The G III 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.
 

    The airplane burns about 5,500 lbs the first hour, 3,800 lbs the second hour, 3,500 lbs the third hour, then 3,000 lbs per hour thereafter.  Low altitude holding requires 4,000 lbs / hour fuel flow.  This gives you 7 hours range with an hours worth of holding fuel, or and hour and 15 minutes reserve according to the regulations.  I once made a 6 hour flight at Mach 0.80 and landed with two hours reserve.  This will take you  more than 3,000 nautical miles at normal cruise.  Use of  long range cruise will result over an hours worth of additional flight time, but only about 4% increase in range.   I know of flights of 8 hours duration that landed with legal fuel reserves.  The G III is quite an airplane.  Thank God it has a bathroom.
 

    The Gulfstream III 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.
 

Note:  Use of the Aux Pump to operate the Landing Gear on the ground is limited 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.
 

Overview

    The "AC" G-III is equipped with three "Generators".  These "Generators" are actually alternators.  They produce "AC" power.  The engine driven "AC" generators produce variable frequency AC power.  The APU Generator produces 400 cycle constant frequency AC.  The G-III is equipped with two Nicad batteries for starting the APU and for emergency power if required.

Converters

    Each of the two "Converters" receive variable frequency AC from their respective alternator.  These converters each produce up to 23 KVA of 115 Volt 3 phase 400 cycle AC power, and up to 250 amps of 28 volt DC.  This AC and DC power is routed through the "Power Distrabution Box".

Power Distribution Box

    The power distribution box receives power from the left and / or right converter, or the APU alternator, and powers the single phase 400 cycle "E" inverter, the 28 volt 300 amp TRU, or transformer recitfier unit, as well as the left, right and essential AC and DC busses.

Batteries / Battery Charging

    The two nicad batteries are each 20 cell, 24 volt 40 ampere hour capacity.  They are controlled by their own respective switch capsules located on the Electric Power Management Panel, or EPMP.  Each battery has it's own battery charger.  The batteries are charged quite differently than on the G-II and earlly model G-III aircraft.
    These battery chargers operate between 20 volts and 33 volts in order to provide a charging current of 38 amps for each battery.  When the charge cycle is complete, the battery ampmeter should read zero, and the voltage should be only slightly more than 27.5 volts.   If the battery voltage drops below 23 volts, the charging cycle is repeated.  The charging rate will always be 38 amps.  The time involved in the charging cycle is what will vary based on the state of the batteries at the time the charging cycle is initiated.  The battery must be at or above 4 volts for the charging cycle to initiate.
    The battery chargers may also function as Transformer-Rectifiers to power the aux hydraulic pump.  Any requirement for DC power over and above the 50 amps each battery charger can provide is taken from the batteries.

Emergency Transformer-Rectifier

    An emergency transformer / rectifier is installed.  When provided with AC power from the power distribution box, it can provide up to 300 amps of 28 volt DC power.  This can power the left, right and essential DC busses.  This is normal when using the APU to power the airplane on the ground.  It would be considered an alternate or emergency proceedure in flight.

Electrical Power Management Panel

    The "EPMP" is located on the overhead panel on the captain's side of the cockpit.  (Flight Deck for those of you obcessed with political correctness).  It contains the battery switches, aux power switch, left and right power switches, electrical annunciators gauges and indicators for the electrical system.  It communicates with the power distribution box in order to control the electrical system, and advise the crew of what is powered by various normal and abnormal or emergency means.  It looks much more complicated than it is.  Most of what you do is set it up and let it do what it was designed to do.  Not a whole lot of pilot intervention is required, other than maybe starting the APU and pressing the AUX power switch if necessary.

Remote Power Supply

    The EPMP is equipped with a remote power supply.  The remote power supply can power the EPMP with either of two power supply boards.  The boards can receive power from the Essential DC Bus, or from the # 1 or # 2 battery.  A third card can power the failure detection circuits and the lighting / dimmer control for the EPMP.

Avionics  Inverters

    Two avionics 500 VA inverters are installed. # 1 AV INV is powered by the ESS DC Bus.  # 2 AV INV is powered by the Right Main DC Bus. If the # 1 AV INV fails, the backup source is the A phase of the ESS AC Bus.  For the # 2 AV INV, the backup is the A phase of the right main AC Bus.

Emergency  Inverter

    An emergency inverter is provided.  It provides single phase 800 VA AC power to the ESS AC Bus.  It recieves power from the ESS DC Bus.  It is intended to provide only the AC power for the items concidered essential for flight.

Ground Operation

    On the ground, unless the engines are running, your choices of electrical power are, External AC, External DC or APU alternator.  External AC and the APU alternator work much the same as far as the G-IV is concerned.  The AC power is routed through different branches of the same circuitry.  It powers the main AC busses.  The right main AC bus then powers the # 2 battery charger.  The Left Main AC bus powers the # 1 battery charger and the TR unit.  The TR unit then powers the Left, Right, and Essential DC busses.
    External DC powers the Left and Right Main DC busses, and through the Left Main DC bus, powers the essential DC bus.  The essential DC bus powers the "E" inverter.  The "E" inverter powers the Essential AC Bus.  The main AC busses are not powered when using external DC power.
 
 

AC Generators

    The "Generators" on the G III are really just huge slightly more sopisticated cousins of the alternators on your family car.  They really are alternators, producing AC power.

FLD :BRG - Failed Bearing - These generators have both primary and auxiliary bearings.  This is basically one bearing inside another.   If the primary bearing is failing, and you have an MEL, you can operate for a maximum of 30 hours until repairs must be made.  You are limited to 250 amps during this period.

O.V. - Over Voltage.  Alerts crew that the generator trip was due to over voltage of 31 volts or more.  You may attempt to reset this one time only.  If it fails again, trip the generator and leave it off until repaired.

F.D. - Failed Diode - One of the diodes in the generator has failed, either open or shorted.  By accessing the voltage regulator and placing the emergency switch to OVERRIDE, you may be able to use the generator for 30 hours at a maximum of 250 amps.

DC System
 

    The Gulfstream II-B 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.

Engines

    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.  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.     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.
 

Wings

    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.

Windshields
                                                                                Check this data for the AC Model
    Rain removal is performed with electrically powered windshield wipers.  The left wiper motor is powered by the Ess DC Bus, and the right is powered by Main DC.  The windshields are also heated electrically.  They are heated with power form the right alternator bus.  Windshield heat is for anti-ice and defogging.  The windshield heat is not necessary for bird strike protection on the G III.  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 left front and right side windows share the same temperature controller.  The right front and left side windows do the same.  Each controller receives power from two of the three phases of AC power.  A green advisory light illuminates when a specific window is being heated.  The lights may be tested with the warning lights test button.  If a particular light tests OK but does not come on, it may indicate that the particular window is at the proper temperature and is not being heated at that moment.  If the light remains out for a long period of time at high altitude, the heat for that window has probably failed.

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 pitot heat is on, the EPR pitot tubes are also heated.  The pitot heaters receive the same power in flight or on the ground, as long as they are turned on.  Do not use them on the ground for extended periods.  Pitot heat is to be turned on just prior to taking the active runway, and turned off after clearing the runway after landing.
    The AOA heaters, when on the ground, receive only 25% of the power they receive when the aircraft is in flight.  They can and should be turned on after the engine start check is complete, and left on until shutdown.

Pressurization

  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!
 
 

    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 two selector switchs and two rheostats on the overhead panel.  The switch positions are "OFF", "AUTO", and "MANUAL" for the CKPT and CABIN, as each have their own switch.  There is a small switch between the temperature control rheostats.  This switch selects the temperature sensor that drives the "Cabin Temp" gauge.  With both switches in "AUTO", the system works as intended.  The cockpit thermostat regulates the temperature in the cockpit, and the cabin thermostat does the same for the cabin.  When one of the switches is placed in  "MANUAL" , that system takes it's orders from the other controller. This remains true regardless of the position of the other switch.   When a particular system is selected "OFF", that system drives it's temperature control valve to full cold.  The controller, however, may still be used to regulate the temperature of the other system should that other system be switched to "MANUAL".  Full cold  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 due to hypothermia..  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.  Do not show the cabin attendant where these valves are.  They are for use only by the flight deck crew and only when both automatic systems have failed.
 

    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.