L Main AC bus fault synoptic, from FlightSafety G450 Pilot Training Manual, figure 2-54, sheet 1.
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:
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:
- 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.
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.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
DU2 is gone and you have the following CAS:
AC Power Fault, L-R
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.
[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.
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