Electrical Abnormals
- James Albright (a former G450 driver)
Updated: 2014-04-12
After years of getting it so wrong, Gulfstream got this system exactly right starting with the GV. It seems they have retained the basic system on every airplane that has followed and that is a good thing. The QRH is laid out very nicely and in the very rare event you have a problem, it should serve you well.
Everything here is from the references shown below, with a few comments in an alternate color.
AC Bus Power Fault
You can handle this if you think it through. By all means accomplish the QRH steps which will leave you with an unpowered main AC bus, standby AC bus, a discharging E-Batt, a stack of CAS messages, and a decision to make if you are in icing conditions. The checklist has improved over the years, but there are still other things to consider.
The E-Batts will be on because the essential DC was momentarily unpowered. Re-arm the E-Batts.
Unlatch the frozen DU (left or right) by pressing the display controller (left or right) 2/3 key for a few seconds.
If the engine is in ALT control mode, restore it by hard selecting ALT control and then back to EPR mode in the SENSOR page of the display controller.
Pay particular notice to the STAB FAIL message on the CAS and vow to not touch the flap handle until you address the stabilizer. The QRH, page ED-21, has you arm the EMER STAB switch to match flap position. There is more to this checklist too:
Arm the EMER STAB switch, which changes your yoke trim switch to a stabilizer switch.
Turn electric trim off.
Use the yoke switch to move the stabilizer to the 10° flap position, then move the flaps to 10° while manually trimming the pitch control forces. Repeat this process for 20° of flaps.
Turn the electric trim on, turn the EMER STAB off. You can now trim the airplane normally.
Plan on a 20° flap approach and landing.
If you are in icing conditions and you are sure the source of the fault was not on the standby AC bus, you can restore the missing standby AC bus by activating the HMG:
In the simulator with an AC bus power fault the main battery will start to discharge with the HMG running without both L and R ESS switches also pressed. I can't see a reason this happens but if you are in this situation you should check the batteries just to be sure.
Symptoms
DU2 is gone and you have the following CAS:
AC Power Fault, L-R
Analysis
Losing a main AC bus brings with it a lot of collateral damage. A left main AC bus fault, for example:
The fault takes out the left essential TRU which is automatically replaced by the auxiliary TRU.
The fault also takes out the left main TRU which leaves the left main DC bus unpowered until you use the TRU control switch. When the DU comes back, it will more than likely be latched.
Because you've lost the main AC bus for good, you've lost stabilizer trim and the left battery charger for good. If you neglect to deal with the STAB TRIM FAIL message you will end up with a FLAPS FAIL instead.
You've also lost the left standby AC bus, which you can get back if you are confident the fault was on the main AC bus. If you don't elect to restore it, you will lost heat to the pilot's TAT probe, left pitot, pilot's windshield, and copilot's side window.
The associated engine might be in ALT control mode.
Procedure
[G450 Airplane Flight Manual, page 03-04-40]
AC Power Synoptic Page . . . SELECT AND CHECK
DC Power Synoptic Page . . . SELECT AND CHECK
IF AN AMBER ″L-R AC POWER FAULT″ MESSAGE IS DISPLAYED ON CAS, AND THE ASSOCIATED MN TRU AND MN DC BUS ARE VERIFIED AS NOT POWERED, PROCEED AS FOLLOWS:
Associated TRU Control Switch . . . SELECT
The amber L-R AC Power Fault message indicates a fault has been detected on the Left Main (L MN) or Right Main (R MN) AC bus. Selecting the associated TRU control switch allows power from the opposite MN AC bus to supply power to the affected MN DC bus.
Emergency Batteries . . . ARM
Note: If the Main AC BUS is not powered it will be necessary to select EMER STAB to operate the flaps and enable the pilot or copilot trim switches to reposition the STAB to match the FLAP position.
It will be necessary to unlatch the display format configuration conversion by holding the display controller "2/3" selection switch capsule in the depressed position for three (3) seconds.
AC Power Fail, L-R
I've never seen a generator on this airplane exceed 30% in normal conditions which tells me one generator should be able to power everything. That being said you will be vulnerable to losing the remaining generator.
If you have an airplane that allows inflight use of the APU in this situation, descending and firing it up should be a no brainer. If you need the gas and can't descend, you are going to have to do without the hot coffee.
But what about oceanic operations? If you lose the remaining generator you will end up on the HMG which means you are going to need that APU eventually and all that is going to complicate matters, isn't it? If it were me, I would be planning on the descent to 37,000' before I find myself without the 40 kVAs. If you look at your fuel charts, the penalty for descending from the forties to 37,000' isn't that bad.
Symptoms
You have the following CAS:
AC Power Fail, L-R
The synoptics should show the affected generator in amber but the other IDG should pick up the load. In flight the only other evidence should be loss of power to the galley and perhaps the cabin, depending on outfitter options.
Analysis
[G450 Aircraft Operating Manual § 2A-24-20 ¶2.C.]
The GCUs provide control, monitoring, test and indication functions for the generators.
The GCUs protect the AC buses by monitoring the quality of power produced by the associated generator. If generator performance does not meet specified parameters, the GCU will not permit power to be supplied to the AC buses.
Some generator protective features incorporate a time delay after the generator is removed from the aircraft AC buses. When a GCU determines that the power output from the generator is again within acceptable parameters, the generator is made available to power the aircraft buses. Normal generator to bus configuration may be restored by cycling the AC RESET push button on the overhead ELECTRICAL POWER CONTROL PANEL.
[G450 Maintenance Manual, §24-25-01 ¶2.A.] The GCU can be reset from a fail-safe condition when power is removed from the GCU or when the left/right generator control switch is operated from off to on. This reset causes the software to re-initialize. If the conditions that caused the microprocessor fail-safe are still present, the microprocessor will fail-safe again.
Procedure
[G450 Airplane Flight Manual, page 03-04-10]
With one (1) generator inoperative, monitor and limit loads to less than 100% AC. Accomplish this by switching off equipment as necessary.
AC Power Synoptic Page . . . SELECT AND CHECK
Affected GEN . . . OFF THEN ON
This resets the GCU
AC/DC RESET Switch (Lighted or Unlighted) . . . PUSH
This permits restoring the generator to the bus.
If proper power is produced, automatic bus transfer back to the normal configuration will occur.
If voltage is not produced or voltage / load indication is abnormal:
Affected GEN . . . Select OFF / OFF not displayed
If above 37,000 ft, consider descending to APU starting altitude to supplement operating generator.
If both generators fail, see Dual Generator Failure.
Battery or Battery Charger Failure
You spend most of your G450 time with the battery doing nothing so no big deal, right? Well, not so fast. Each battery provides you with insurance: two APU starts and 30 minutes of operating time. If something is wrong with the charger and the battery is discharging, I would do everything I could to save the battery. Pull the CB or turn the battery switch off!
Symptoms
You might have a discharging battery amp meter or the following CAS:
Battery Charger Fail, L-R
Analysis
[G450 Aircraft Operating Manual, §2A-24-30 ¶2.D.]
The batteries are rated as 24V DC, 45 amp/hour. During normal operations, the main batteries are used to power the essential DC buses prior to starting the APU to provide APU fire detection and fire extinguishing. (The APU start contactor is powered only by the left battery during the starting process unless the left battery is manually selected off or not connected or installed, in which case the right battery will power the APU start contactor).
The battery chargers operate as TRUs, converting 115V, 400 Hz, 3Ø AC into 28V DC to maintain main battery charge. The left charger is powered by the left main AC bus, the right charger by the right main AC bus. The chargers will begin to operate if battery voltage drops to 23V and will replenish an almost discharged battery in approximately 90 minutes. The main battery chargers will also aid in starting the APU or powering the AUX hydraulic pump by providing an extra 40 amps in addition to battery power, provided the main AC buses are powered. This feature could also be employed in the unusual circumstance of loss of TRU input to the essential DC buses, requiring the batteries to power essential DC with main AC TRUs powering the main DC buses. Protective features in the battery chargers will prevent damage to the aircraft batteries.
The batteries should not drain during normal flight operations with the auxiliary hydraulic pump and APU starter off. They stand in reserve to power the DC essential buses if needed.
Procedure
[G450 Airplane Flight Manual, page 03-04-60]
DC Power Synoptic Page . . . SELECT AND CHECK
Verify the affected side (L or R) MN AC BUS is powered.
Associated BATTERIES VOLTS / AMPS . . . CHECK
If reading is abnormal:
Associated Battery Charger CB . . . PULL
After 3 - 5 minutes:
Associated Battery Charger CB . . . CLOSE
If battery does not charge:
Associated Battery Charger CB . . . PULL
If battery is discharging:
Associated MAIN BATTERY . . . OFF
NOTE: If battery power is required, return associated MAIN BATTERY to ON.
Essential DC Bus Failure
By all means go through the QRH procedure, it could work. But if you end up without the bus, you should suspect a short in a system powered by that bus. Going through the Master Table of Electrical Component Availability, EA-17, it looks like you are in pretty good shape as long as you have the other essential DC bus.
Now for a bit of controversial thought:
If there is something on that bus you absolutely need back you could pull all the breakers on the affected essential bus and if the bus came back, reset those that you really need.
This was procedure in the GIII.
This is not offered as an option in the G450.
While the QRH does not offer this, the AFM procedure ends with "If the L ESS DC bus failed: the following is a list of Circuit Breakers (CB) on the L ESS Bus" with a table, and another section for the right essential. It sounds like they know you might need to do this, but they aren't recommending it explicitly. Again, if all you are doing is following the QRH, you would never see this.
Symptoms
DU1 or DU4 are gone, the PFD has moved inboard, and that side's display controller and CCD are inoperative.
Analysis
If an essential DC bus loses power from its essential TRU, the AUX TRU should take the load automatically. If that doesn't happen, the battery should take the load. The QRH has you check the battery switches on, they should be. Then it has you try the HMG to force the AUX TRU into action, but it should already have been switched automatically.
You either have a combination of faults (automatic TRU switching, automatic battery switching) or you have a short in a system connected to the affected DC essential bus. That being the case, you want to prepare yourself for landing by give the duties to the side of the cockpit still working.
Procedure
[G450 Airplane Flight Manual, page 03-04-20]
MAIN BATTERIES . . . ON
Standby Electrical Power System (HMG) MASTER . . . ON
HMG L and R ESS Switch(es) . . . AS APPROPRIATE
NOTE: To avoid shock-loading the HMG, make each ESS switch selection one at a time. Allow at least ten (10) seconds between each selection to allow HMG loads to stabilize.
NOTE: Only DU 1 and DU 4 are available when using the HMG. To view synoptic / system pages on DU 4, select the PFD-CMD to L (Left), engage the autopilot (if desired) and select MAP on the copilot display controller. This will result in I-NAV being displayed on DU 4. The copilot Cursor Control Device (CCD) can now be used to control display of 2/3 synoptic pages and 1/6 system pages. The copilot display controller can be used to control display of 1/6 system pages.
NOTE: If the sequence of events leading up to the condition of having the two DUs available involved an electrical break-power transfer, it will be necessary to first unlatch the display format configuration conversion by holding the display controller "2/3" selection switch capsule in the depressed position for three (3) seconds before selecting the MAP switch capsule.
BATTERIES VOLTS / AMPS . . . MONITOR
For approach and landing:
NOTE: If the L or R ESS DC bus is not recovered, the display and navigation capabilities of the respective side of the cockpit will be degraded. If the L ESS DC bus is not recovered, DU #1 will be lost and the PFD will transfer to DU #2; additionally, the Left Display Controller (DC) and CCD will be lost. The lost DC will result in the PFD on DU #2 displaying only default settings that will not be able to be adjusted, other than the altimeter setting that may be changed with the DC BARO knob. If the R ESS DC bus is not recovered, DU #4 will be lost and the PFD will transfer to DU #3 with the same default display limitations. It is recommended that the crewmember on the side with the operating DC and CCD fly the airplane for approach and landing.
Landing Gear . . . DOWN
Flaps . . . SET FOR LANDING
Ground Spoilers . . . ARMED
Speed Brakes . . . MANUALLY DEPLOY
At main gear contact with runway, ground spoilers should deploy automatically. Manual speed brake deployment is a recommended backup procedure.
NOTE: Thrust reversers will be available only if the corresponding Essential DC bus is powered and hydraulic pressure from the corresponding hydraulic system is available, i.e., left thrust reverser operation requires Left Essential DC bus and Left Hydraulic System; right thrust reverser operation requires Right Essential DC bus and Right Hydraulic System.
Dual Generator Failure
The QRH procedure makes great sense but may not even be necessary if you remember the first four steps. Cut the fuel pump draw in half right off the bat in case you are going to end up needing those batteries, then turn the generator control switches off then on, and finally press the AC/DC reset button. If that doesn't work and you haven't already had a hydraulic problem, get the HMG system on, count to ten, get the left essential DC bus back, count to ten, and then the right essential DC. This gets everything back soonest if that is possible and puts you in good shape if it is not.
Symptoms
You will end up with the outboard DUs powered, the inboard DUs dark, and the rest of the cockpit may look like its cockpit preflight state. The most telling symptom will be the two "OFF" capsules in the generator control switches. You can get synoptics by pressing the copilot's display controller MAP button for a few seconds and using the CCD.
Analysis
We used to practice this a lot in the GV, though it has never happened in real life. In any case, it was drummed into our heads: "Four, one, two, three: 4 blank screens, 1 crossflow, 2 boost pumps, 3 HMG switches."
The screens are different but the electrical system is the same so we could do something similar, right? Well Gulfstream has changed its mind on what has priority. You still need to reduce electrical loads (turn the alternate fuel pumps off) right away, but now we want to recycle the GCUs and BPCUs before we try the HMG.
If the two center screens go blank and both generators say OFF, you need to take care of three switches, three times:
Fuel — crossflow valve open, main boost pumps on, alternate boost pumps off
Generators — both generators switches OFF then ON (to reset the GCUs), AC/DC Reset
HMG — Master switch on, wait ten seconds, L ESS, wait ten seconds, R ESS
Get all that done, you should end up in pretty good shape, even you don't get any of those AC electrons back. Even your automatic pressurization works since it is powered by Phase A AC essential. You now have time to pull up the QRH and do things methodically.
Procedure
[G450 Airplane Flight Manual, page 04-04-10]
CAUTION: IN THE EVENT OF A DUAL GENERATOR FAILURE, REMOVE ALL NON-ESSENTIAL ELECTRICAL LOADS.
Crossflow Valve (X FLOW) . . . OPEN
L / R MAIN Boost Pumps . . . VERIFY BOTH ON
L / R ALT Boost Pumps . . . VERIFY BOTH OFF
L / R GEN Switches . . . OFF THEN ON
AC / DC RESET Switch (Lighted or Unlighted) . . . PUSH
If power is NOT restored:
CAUTION: APPROXIMATELY THIRTY (30) MINUTES OF ELECTRICAL POWER IS AVAILABLE IF BOTH BATTERIES ARE FULLY CHARGED AND STANDBY ELECTRICAL POWER SYSTEM (HMG) CANNOT BE USED.
If Left System (L SYS) or PTU hydraulic fluid and the Standby Electrical Power System (HMG) are available, proceed with Step 6.
If L SYS or PTU hydraulic fluid is not available, the Standby Electrical Power System (HMG) will not be available, proceed to Step 14.
Standby Electrical Power System (HMG) MASTER . . . ON
NOTE: To avoid shock loading the HMG, make each ESS switch selection one at a time. Allow at least ten (10) seconds between each selection to allow HMG loads to stabilize.
Standby Electrical Power System (HMG) L / R ESS Switch(es) . . . ON
NOTE: Only DU 1 and DU 4 are available when using the HMG. To view synoptic/system pages on DU 4, select the PFD-CMD to L (Left), engage the autopilot (if desired) and select MAP on the copilot’s display controller. If FMS1 or FMS3 is selected, this will result in I-NAV being displayed on DU 4. The copilot’s Cursor Control Device (CCD) can now be used to control display of 2/3 synoptic pages and 1/6 system pages. The copilot’s display controller can be used to control display of 1/6 system pages.
NOTE: If the sequence of events leading up to the condition of having the two DUs available involved an electrical break-power transfer, it will be necessary to first unlatch the display format configuration conversion by holding the display controller “2/3” selection switch capsule in the depressed position for three (3) seconds before selecting the MAP switch capsule.
Autopilot (If Desired) . . . ENGAGE
Copilot’s Display Controller . . . SELECT MAP
Copilot’s Cursor Control Device (CCD) . . . SELECT AC POWER SYNOPTIC PAGE
Standby Electrical Power System (HMG) / AUX TRU LOAD . . . LESS THAN 100%
Copilot’s CCD . . . SELECT DC POWER SYNOPTIC PAGE
Left / Right Battery Volts / Amps . . . CHECK
With the APU generator inoperative, electrical power will not be available to the L Main AC Bus, R Main AC Bus, L Main DC Bus or R Main DC Bus.
The Standby Electrical Power System (HMG) is supplying power to the L ESS DC Bus, R ESS DC Bus, L STBY AC Bus, R STBY AC Bus and Phase A of the ESS AC Bus. Among the items available: (see the figure below)
NOTE: Radar will be inoperative.
NOTE: If landing with the HMG operating and the APU inoperative, proceed to 03-15-40, Landing With The Standby Electrical Power System (HMG) Powered From The Left Or Both Hydraulic Systems. If HMG is being powered by the PTU (i.e. Left System failure coupled with dual generator failure and APU inoperative), see Section 03-15-50, Operations With The Standby Electrical Power System (HMG) Powered From The Right Hydraulic System Only and Section 03-15-60, Landing With The Standby Electrical Power System (HMG) Operating On Right Hydraulic System.
If L SYS or PTU Hydraulic Fluid is not available, the Standby Electrical Power System (HMG) will not be available, proceed as follows:
E-BATTS . . . OFF / ARM
CAUTION: CONFIGURE ELECTRICAL SYSTEM TO STAY AT OR UNDER 100% LOADING OF AC AND DC POWER.
APU . . . START
NOTE: Initiate start attempt at or below 37,000 ft.
APU Generator . . . ON
If both main batteries fail, See section 04-04-30, Operation on Emergency Power Only.
If APU fails to start or APU generator and Standby Electrical System (HMG) is inoperative, proceed to Step 23.
If APU starts and APU generator is operative:
Standby Electrical Power System (HMG) L ESS / R ESS . . . OFF
Standby Electrical Power System (HMG) MASTER . . . OFF
AC Power 2/3 Synoptic Page . . . SELECT
L / R MAIN and ALT Boost Pumps . . . ON
APU Generator Load . . . LESS THAN 100%
Crossflow Valve (X FLOW) . . . CLOSED
If APU fails to start or APU generator is inoperative and Standby Electrical Power System (HMG) is inoperative, configure airplane electrical power system for operation on main batteries power as follows:
CAUTION: WHEN ANY ELECTRICAL CONDITION REQUIRES OPERATION ON MAIN BATTERIES ONLY, LAND AT NEAREST SUITABLE AIRPORT.
Altitude . . . ESTABLISH 15,000 FEET OR BELOW
L / R MAIN Boost Pumps . . . OFF
Emergency Power ARM . . . VERIFY ARMED
Main Batteries . . . ON
All Non-Essential Items . . . OFF
NOTE: DUs 1 and 4 are powered by the batteries. Consideration should be given turning one or both DUs OFF if the situation permits.
NOTE: The airplane batteries will power the L ESS DC bus and R ESS DC bus for approximately thirty (30) minutes if two (2) APU start attempts have been made, with each attempt lasting not longer than thirty (30) seconds.
NOTE: When operating on batteries only, both FADECs hard-revert to the alternate control mode.
NOTE: Thrust reversers will be available only if the corresponding Essential DC bus is powered and hydraulic pressure from the corresponding hydraulic system is available, i.e., left thrust reverser operation requires Left Essential DC bus and Left Hydraulic System; right thrust reverser operation requires Right Essential DC bus and Right Hydraulic System.
(From Step 13, above)
Generator Overload
Getting rid of a high draw item also has the salutary effect of identifying the root cause of the problem, if you are methodical about it. You should pull up the synoptic and watch the load on the generator as you switch off your high draw suspects.
The easiest ones to get rid and probably one of the higher draws are fuel boost pumps. How much should a fuel pump reduce your load? I watched the right generator and right main TRU while shutting off the right alternate fuel pump. The generator dropped from 24% to 21% load, the TRU from 21% to 12%.
I would kill the on-side alternate pump, look at the load, and if it goes down appreciably — much more than the expected 3% AC — suspect it. If, for example, the load goes from over 100% to under 30%, you have just identified a pump that is drawing way too much and could be a fire hazard; leave that breaker pulled and consider yourself lucky. If it only goes down a few percent, open the crossflow valve and kill the on-side main boost pump. If you still only end up with a negligible reduction, bring one of the pumps back and keep looking.
How do you know what the high draw items are? Look at the number on the circuit breakers. But doing that you see mostly small numbers. There are just a few over 20, such as the windshield heaters, PSU fans, and even the vacuum toilet. One big draw item that should be an easy kill are the HF R/T units, 25 each. The source of really big numbers, however, is the PDBs. Here's the left:
Most of these are feeders to other circuit breaker panels but there are a few worth noting: fuel pumps and the galley.
Symptoms
Generator Overload, L-R
High load indicated on affected IDG.
Analysis
Each AC generator normally runs at less than 30% of capacity so something has gone wrong. The high draw AC items, we are often told, are "heaters, motors, chargers, and pumps." Looking at the Master Table of Electrical Component Availability, EA-17, we see the following items from those categories under L MN AC, R MN AC, and ESS AC:
Pitot Heat
STAB
WNDSHLD HT
Missing from this list are the four TRUs, which each get their power from a main AC bus. And of course that means all on-side electrical loads are suspect.
Procedure
[G450 Airplane Flight Manual, page 03-04-30]
AC Power Synoptic Page . . . SELECT AND CHECK
Affected Bus(es) . . . REDUCE LOAD
References:
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013