B777 Undifferentiated or Other Model
Flight Crew Last 90 Days 45; Flight Crew Total 13000; Flight Crew Type 1000
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft
We were leveling at 15;000 feet and in the process of completing the final portion of the standby electrical power checks by turning off the fourth generator. We were expecting the Captain to retain his PFD/ND; L CDU; Left VHF and upper EICAS. Instead we lost power to everything in the aircraft except the clocks and the ISFD (Integrated Standby Flight Display). We immediately restored all four generators. Within approximately 20 seconds the FO's side of the aircraft was restored along with the lower EICAS; R VHF and the R-transponder. The Captain's side remained unpowered. The FO took over flying and talking responsibilities on the Captain's direction. We had initially lost all COM with ZZZZ radar and had turned back toward Airport ZZZZ remaining at our last assigned altitude of FL150. We determined that the RAT had deployed as expected but the flight control system remained in Normal mode vs reverting to Secondary mode which is normally what happens when you turn off all 4 generators. Therefore; we were able to re-engage both the autothrottles and autopilot. The FO also had his Flight Director. We were unable to call up any Electronic checklist or system synoptic pages. We analyzed our situation by using the FM contained in content locker on our iPads. We re-established communications with ZZZZ radar and terminated the remainder of the test profile. While proceeding to the ZZZZ intersection for the approach we sent the [Contract Engineer] that was onboard into the E&E (Electronics and Engineering) compartment to check for any problems. Everything appeared normal to him and he elected to hit the P310 panel with an empty plastic water bottle to see if it would affect any potentially stuck relays. Amazingly that did restore the Captains side of the aircraft. No CBs were cycled. Once we had regained the Captain's systems he took over flying the jet and we made a normal hand flown full stop landing.
B777 FO reported they lost all power to the aircraft; indicating a problem with backup systems; during a test flight when they turned off all four generators.