Date: 202006
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: Generator Drive
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Time Pressure; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: Taxi
Result: General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Company Policy; Human Factors; Environment - Non Weather Related
Primary problem: Aircraft

Narrative: We were scheduled for a ferry flight from ZZZ - ZZZ1 at XA00 local. Due to our current situation; I have not flown a lot lately; and as a new Captain; have not done a ferry flight. I showed up early; as there are extra things to do on a ferry; and my FO was DH and not scheduled to land until 40 minutes prior to our scheduled departure. I had contacted him the day before to say we would meet at the aircraft.I called Dispatch to check whether this was a repositioning ferry or a maintenance ferry; because the release just said ferry and there was a log entry saying it required a maintenance action. Dispatcher told me that it was just a repositioning flight. I went to the aircraft and cleaned; performed the initial preflight and checked all the switches (finding several things out of place) and circuit breakers. I initialized the ACARS and started my preflight flow. When I checked the last maintenance release form it was dated [date]. While I was loading the FMC the printer started sending a quite lengthy maintenance ferry document; and at some point after that a mechanic came in. He talked about the lengthy maintenance ferry document and I asked to verify it was a maintenance ferry and he said yes because the aircraft had 2 checks that were overdue. He discussed with me that there were no maintenance items that would affect the operation of the aircraft. He also let me know the aircraft had been in storage since the last flight. I called Dispatch back to let her know we were a maintenance ferry; and asked if it needed to be on the release as such. Dispatcher thanked me for keeping her in the loop and said no it didn't; and we were good with the release as is.As I started through the maintenance ferry document my FO showed up. I told him to get settled and I would catch him up on where we were. I said I had just started to go through the maintenance ferry document and it was going to take some time; it was 1X pages; out of sequence; and interspersed with things I had printed. I thought the ACARS copy had to be in the book also. There were a lot of major systems that had been disabled and circuit breakers pulled and reset; and I didn't want to rush through; needed to make sure everything had been signed off.He expressed concern that we were not going to get out on time and that his DH ZZZ1-ZZZ2 was the last flight that day. He was a little upset that they had called him to fly all the way from ZZZ2 to fly a 1 hour flight on his last day of reserve. I said we would try our best; but the aircraft had just come out of storage and we needed to be thorough; this and the flight being a ferry flight were operational threats. He went back to check the cabin for ferry items. The agent closed us up and the FO armed the doors; and I went to check them as well. We got all our tasks completed and did push late. Pushback and start were normal; we did the after start and I asked for taxi clearance. Then the R Gen Off EICAS message came on. I asked him to tell Ground Control that we had a maintenance item and needed to run a checklist; and to run the Gen Off checklist. He talked to Ground as he got the checklist; and just then we lost all electrics. I tried to start the APU but it would not start.Both engines were running; both generator switches were on; but we had only battery power. We decided to return to the gate; and the FO told Ground. He asked Ground if we were ok there for a few minutes; they said yes. Then he called operations to tell them we were returning to the gate. We also noticed the aircraft shaking; but only had backup engine instruments and could not check the vibration indications as all screens had gone blank. I had thought it was wind but looking outside; there really wasn't much. Standby instruments looked good. There was a delay while operations said they were deciding where to put us; and I heard him say we wanted to go back. After that he told Operations something along the lines of; 'well then; weare a priority handling aircraft.' I did not ask to get priority; nor was I asked if that was what we should do. I didn't feel we were ever in danger; and the FO subsequently told me that he said that he did it; so we could get our gate back because our screens had failed. I believe part of the issue was time pressure to get home.Not being sure what was going on with the aircraft; we chose to shut down the engines to be on the safe side. It may not have been necessary at the time; but we were right by the gate and there was no traffic that we were blocking. I thought about running the checklist and getting a gen back; but with the aircraft shaking also; decided against it. I told ground what we were doing; and called operations for a tow in. Ground asked if we needed anything and we declined. No equipment was requested; no assistance received. Maintenance subsequently replaced the right GCU but could not find a reason why the left gen dropped off also. They said the APU had a fault; which they cleared. They said the shaking was simply due to the aircraft being so light; no cargo; passengers; galleys; and not a lot of fuel; with the engines running. It was unlike anything I had felt before; but we were only 153;000 lbs; and I have never been that light; but they said that is what happens when they run engines with empty aircraft. They started both engines to see everything was normal and test the electrics and power transferring. APU started normally; engines were fine; and electrics fine except that the right gen needed to be cycled to get it to come online. As I was asking one mechanic about that; as it was not normal; they were shutting down. They restarted the right engine to check it again; and this time the gen came online normally. They said sitting for a while may have been the cause of the some of these issues; but all was operating normally now.We got the aircraft ready to go; waited a while for a new release form; and flew to ZZZ1 uneventfully.I'm concerned about the priority handling; and to Operations; not ATC. It was busy but I feel I should have rescinded that.




Synopsis: Air carrier Captain reported experiencing mechanical problems after pushback resulting in a return to gate.