Dual generator failure, from Eddie's notes.
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.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
You will end up with the outboard DU's powered, the inboard DU's 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.
We used to practice this a lot in the G-V, 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:
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. What follows then are the steps from the QRH with a few editorial comments in blue.
[G450 Airplane Flight Manual, page 04-04-10]
CAUTION: IN THE EVENT OF A DUAL GENERATOR FAILURE, REMOVE ALL NON-ESSENTIAL ELECTRICAL LOADS.
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.
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’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.
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:
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.
CAUTION: CONFIGURE ELECTRICAL SYSTEM TO STAY AT OR UNDER 100% LOADING OF AC AND DC POWER.
NOTE: Initiate start attempt at or below 37,000 ft.
If both main batteries fail, See section 04-04-30, Operation on Emergency Power Only.
CAUTION: WHEN ANY ELECTRICAL CONDITION REQUIRES OPERATION ON MAIN BATTERIES ONLY, LAND AT NEAREST SUITABLE AIRPORT.
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.
FSI G450 PTM, FlightSafety International Gulfstream G450 Pilot Training Manual, Volume 2, Aircraft Systems, October 2008
FSI G450 MTM, FlightSafety International Gulfstream G450 Maintenance Training Manual, August 2008
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Airplane Flight Manual, Revision 36, December 5, 2013
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013