A CPR G3 FLC HAS A MAJOR ELECTRICAL FAILURE THAT EVENTUALLY RESULTS IN THE LOSS OF ALL INSTS; NAV EQUIP AND COM EQUIP. THE FLC SUCCESSFULLY COMPLETED A VISUAL APCH TO MGM WITH NO INJURIES OR DAMAGE.

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WHILE CRUISING AT FL350; L HAND EFIS TUBES BEGAN FLICKERING VIOLENTLY AND DISPLAY BEGAN TO DISAPPEAR. PNF LOOKED UP ON ELECTRICAL PWR MGMNT PANEL AND NOTED THAT 'DC RESET' ANNUNCIATOR WAS ILLUMINATED AND BOTH BATTERIES WERE DISCHARGING RAPIDLY (APPROX 48 AMPS PER SIDE). BOTH BATTERY #1 AND BATTERY #2 SWITCHES WERE ILLUMINATED; INDICATING THAT BATTERY TIE BUS WAS POWERED. OFF FLAGS APPEARED ON L HAND AIRSPD INDICATOR; L HAND ALTIMETER; L HAND VSI; L HAND RMI. LOST CHANNEL #1 OF AUTOPLT (INCLUDING PITCH TRIM). LOST #1 NAV; #1 COM AND #1 ADF. TRIED 'DC RESET' TO NO AVAIL. SHORTLY AFTER (WITHIN A FEW SECONDS); COM #3 (WHICH WE WERE COMMUNICATING ON) AND XPONDER #1 FAILED. TRIED TO RE-ESTABLISH COM WITH ATC USING COM #2. WAS UNABLE TO RE-ESTABLISH COM BY USING HAND MIKE OR HEADSETS. DECISION WAS MADE TO SQUAWK 7700 AND BEGIN DSCNT TO ALT WHERE APU COULD BE STARTED. PNF SQUAWKED 7700 AND DIRECTED PF TO MAINTAIN ALT FOR APPROX 2-3 MINS WITH THE HOPES THAT ATC WOULD CLR THE AIRSPACE BELOW AND IN FRONT OF US. PNF REDUCED ELECTRICAL LOAD AS MUCH AS POSSIBLE. PNF CHKED CIRCUIT BREAKERS ON PWR DISTRIBUTION BOARD. NO CIRCUIT BREAKERS WERE POPPED ON PWR DISTRIBUTION BOARD. WE BEGAN DSCNT TO 15000 FT AT A RATE OF APPROX 2000 FPM. SHORTLY AFTER; ENTIRE ELECTRICAL PWR MGMNT PANEL WENT BLACK; AS WELL AS ALL INDICATIONS ON THE PRESSURIZATION (CABIN PRESSURE CTLR). MASTER WARNING PANEL WAS ILLUMINATED 'CAB PRESS MAN' BUT WE HAD NO MANUAL CTL OF THE OUTFLOW VALVE. OUTFLOW VALVE WAS STUCK IN CTR POS. WE ALSO LOST ALL ENG INSTS. KNOWING THAT WE HAD CROSSED TLH A FEW MINS BEFORE (10-15 MINS BEFORE); PIC DECIDED TO USE DOTHAN OR MONTGOMERY AS A LNDG ALTERNATE. SIC CONTINUED TO FLY ACFT AND PIC PULLED PLATES FOR DOTHAN AND MONTGOMERY. PIC CALLED HANGAR PERSONNEL USING THE FLT PHONE AND NOTIFIED THEM THAT WE HAD A MAJOR PROB AND NEEDED EMER ASSISTANCE WITH COMS. PIC BRIEFED HANGAR PERSONNEL ON PROB AND REQUESTED THAT THEY GET SOMEONE TO NOTIFY ATC OF OUR PROB AND OUR INTENTIONS. PIC GAVE SIC A HEADING TO FLY FOR MONTGOMERY (AT THE TIME; WE WERE DSNDING THROUGH THE 20'S AND WERE PASSING ABEAM DOTHAN). HANGAR PERSONNEL OBTAINED CURRENT WX CONDITIONS AT MGM INCLUDING CEILING; ALTIMETER AND WIND SPD AND DIRECTION. THIS INFO WAS OBTAINED VIA TELEPHONE FROM MGM APCH CTL. DURING DSCNT THROUGH THE 20'S; WE LOST CDU #3. SHORTLY THEREAFTER WE LOST CDU #1. DSNDING THROUGH 21000 FT PIC DIRECTED PAX WHO WAS SITTING ON THE JUMP SEAT TO GO TO THE BACK AND TELL LEAD PAX THAT WE HAD AN ELECTRICAL PROB AND TO ASK HIM TO MAKE SURE EVERYONE WAS BUCKLED UP AND STAYED IN THEIR SEATS; AND THAT WE WOULD BE LNDG IN APPROX 15 MINS. PIC INSTRUCTED JUMP SEAT PAX TO FIND A SEAT IN THE BACK AND STAY THERE UNTIL WE LANDED. AT 15000 FT PNF ATTEMPTED APU START WHICH WAS UNSUCCESSFUL. (NEVER GOT ANY INDICATION THAT APU DOOR WAS OPEN.) WE CONTINUED DSCNT TO 10000 FT. AT APPROX 33 NM SE OF MGM; PIC HUNG UP PHONE WITH HANGAR AND CALLED ATC DIRECTLY (MGM APCH). PIC BRIEFED CTLR OF SIT AND CTLR CLRED US PLT'S DISCRETION TO 2000 FT. WE WERE SWITCHED TO FINAL CTLR AND WERE GIVEN VECTORS FOR ASR APCH. PIC INFORMED SIC THAT GND SPOILERS WOULD NOT BE AVAILABLE IF WE DID NOT HAVE L MAIN DC PWR. NOTE -- WHEN GEAR WAS LOWERED; WE COULD SEE THREE VERY DIM GREEN LIGHTS INDICATING GEAR WAS DOWN. FINAL CTLR GAVE US 278 DEG HDG AND 'DSND TO MINIMUM ALT' WHICH WAS 660 FT. A FEW SECONDS LATER; FLT PHONE FAILED AND COMS WERE LOST. WE CONTINUED DSCNT AND BROKE OUT WITHIN A FEW SECONDS WITH RWY 28 IN SIGHT. LNDG WAS UNEVENTFUL. AFTER TOUCHDOWN; PIC TOOK CTL OF ACFT. PIC TAXIED CLR AND TAXIED TO THE GA RAMP AND PARKED THE ACFT. EMER VEHICLES FOLLOWED ACFT TO RAMP. PAX WERE CHKED ON AFTER ACFT WAS SHUT DOWN. NO FURTHER INCIDENTS OCCURRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT OF THIS CPR GULFSTREAM 3 SAID THAT THE K-15 RELAY IN THE MAIN ELECTRICAL SYS APPEARS TO HAVE PARTIALLY FAILED. THE RELAY DID NOT COMPLETELY FAIL AND GULFSTREAM IS STILL RUNNING TESTS ON THE ELECTRICAL SYS WHICH THEY HAVE REMOVED FROM THE ACFT. THE NEW SYS IS WORKING VERY WELL AND GULFSTREAM HAS DESIGNED A MODIFICATION THAT MAY PREVENT SUCH OCCURRENCES IN THE FUTURE. THE RPTR SAID THAT GULFSTREAM IS INSTALLING A PARALLEL K-15 RELAY THAT WILL AUTOMATICALLY TAKE OVER IF THE PRIMARY FAILS. THE MANUFACTURER IS ALSO INSTALLING AN 'ESSENTIAL BUS ON BATTERY' ANNUNCIATOR THAT WILL WARN THE FLC IF THE BATTERIES BEGIN TO PWR THAT BUS. THE FLC DID HAVE A HAND- HELD COM RADIO ON BOARD; BUT IT DID NOT WORK SINCE THERE WAS NO EXTERNAL ANTENNA. THEIR CORPORATION IS CONSIDERING AN INSTALLATION NOW. CALLBACK CONVERSATION WITH RPTR OF ACN 391354 REVEALED THE FOLLOWING INFO: THIS FO WAS FLYING THE G3 WHEN THE ELECTRICAL SYS STARTED TO FAIL AND HE SAID THAT THE FLC DECIDED TO HAVE HIM CONTINUE TO FLY THE ACFT BECAUSE THE CAPT HAD ALREADY LOST MOST OF HIS INSTS AND ALSO BECAUSE THE CAPT WAS CONSIDERED TO BE THE BEST COORDINATOR OF THIS TEAM. THE FO SAID THAT HE FLEW THE ACFT UNTIL IT WAS TIME TO TURN OFF OF THE RWY. THE TIME ELAPSED BTWN THE FIRST SIGN OF ELECTRICAL PROBS TO TOUCHDOWN WAS ONLY 26 MINS ACCORDING TO THE FO. HE SAID THAT THE COMPANY THAT HE FLIES FOR HAS ALREADY STARTED SOME OF THE MODIFICATIONS TO THE ACFT THAT COULD HELP PREVENT THIS FAILURE IN THE FUTURE. HE CREDITS THEIR TRAINING AND THE SUPPORT FROM COMPANY PERSONNEL AND ATC FOR THE SUCCESSFUL OUTCOME. HE SAID THAT THE FAA INSPECTORS FROM THE LCL FSDO AND FROM THE MAINT GROUP INSPECTED THE ACFT AND QUESTIONED THE CREW AND OTHER COMPANY PERSONNEL.