Narrative:

At FL350 northbound to yip, the left generator failed, right generator picked up the load 250 amps. I reduced dc load (galley power and 2 boost pumps xfeed open) and went for checklist. While finding appropriate checklist, right generator failed. Selected thrust reverser on and battery emergency. 0 amps were indicated on thrust reverser ammeter. Center frequency was busy so squawked 7700 and broadcasted on 121.5 that we had double generator failure and cabin climbing and we were making rapid descent. I regained control of pressurization with manual control and thrust reverser amps started to indicate after tapping gauge. Communications were reestablished at about FL250 with ZOB and ZID ARTCC's. Flight terminated at yip without mishap. Suggest tapping gauges right away when abnormal reading experienced. Suggest checking what radios and speakers are affected when battery switch in emergency. Callback conversation with reporter revealed the following information: reporter stated that it was learned upon maintenance review that only 1 generator had really malfunctioned and the other had indicated failure only due to the voltage regulator causing it to go off circuit. The cabin pressure was lost due to the automatic mode being electrically driven. Therefore, when the manual mode was selected the outflow valve was closed and pressure could be regulated. At first, there was no amps indicated from the xformer rectifier pwred by the battery. However, after the ammeter was tapped, it came up and showed amps available which was sufficient for all necessary electrical power to reach their destination.

Related reports:

Google
 

Original NASA ASRS Text

Title: FLC OF A GULFSTREAM II MADE AN EMER DSCNT WHEN FIRST THE L GENERATOR FAILED LIGHT CAME ON DURING HIGH ALT CRUISE AND THEN THE R INDICATING THAT BOTH GENERATORS HAD FAILED RESULTING IN A LOSS OF COMS AND ACFT PRESSURIZATION. BATTERY ELECTRICAL PWR WAS SUBSEQUENTLY ESTABLISHED TO REGAIN COM AND ACFT PRESSURIZATION.

Narrative: AT FL350 NBOUND TO YIP, THE L GENERATOR FAILED, R GENERATOR PICKED UP THE LOAD 250 AMPS. I REDUCED DC LOAD (GALLEY PWR AND 2 BOOST PUMPS XFEED OPEN) AND WENT FOR CHKLIST. WHILE FINDING APPROPRIATE CHKLIST, R GENERATOR FAILED. SELECTED THRUST REVERSER ON AND BATTERY EMER. 0 AMPS WERE INDICATED ON THRUST REVERSER AMMETER. CTR FREQ WAS BUSY SO SQUAWKED 7700 AND BROADCASTED ON 121.5 THAT WE HAD DOUBLE GENERATOR FAILURE AND CABIN CLBING AND WE WERE MAKING RAPID DSCNT. I REGAINED CTL OF PRESSURIZATION WITH MANUAL CTL AND THRUST REVERSER AMPS STARTED TO INDICATE AFTER TAPPING GAUGE. COMS WERE REESTABLISHED AT ABOUT FL250 WITH ZOB AND ZID ARTCC'S. FLT TERMINATED AT YIP WITHOUT MISHAP. SUGGEST TAPPING GAUGES RIGHT AWAY WHEN ABNORMAL READING EXPERIENCED. SUGGEST CHKING WHAT RADIOS AND SPEAKERS ARE AFFECTED WHEN BATTERY SWITCH IN EMER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT IT WAS LEARNED UPON MAINT REVIEW THAT ONLY 1 GENERATOR HAD REALLY MALFUNCTIONED AND THE OTHER HAD INDICATED FAILURE ONLY DUE TO THE VOLTAGE REGULATOR CAUSING IT TO GO OFF CIRCUIT. THE CABIN PRESSURE WAS LOST DUE TO THE AUTOMATIC MODE BEING ELECTRICALLY DRIVEN. THEREFORE, WHEN THE MANUAL MODE WAS SELECTED THE OUTFLOW VALVE WAS CLOSED AND PRESSURE COULD BE REGULATED. AT FIRST, THERE WAS NO AMPS INDICATED FROM THE XFORMER RECTIFIER PWRED BY THE BATTERY. HOWEVER, AFTER THE AMMETER WAS TAPPED, IT CAME UP AND SHOWED AMPS AVAILABLE WHICH WAS SUFFICIENT FOR ALL NECESSARY ELECTRICAL PWR TO REACH THEIR DEST.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.