Air carrier flight crew flying 737 aircraft reported electrical system malfunction inflight. Flight crew diverted and landed safely.
Synopsis
Air carrier flight crew flying 737 aircraft reported electrical system malfunction inflight. Flight crew diverted and landed safely.
Narrative
En route from ZZZ to ZZZ1; we were presented with an intermittent Master Caution and intermittent #1 Transfer Bus Off light. We ran the QRH Checklist Transfer Bus Off. As we were progressing through the checklist; the #1 Transfer Bus Off light was becoming more frequent and more persistent. In accordance with QRH; we confirmed we were in operational limits to start and use the APU for electrical. The limit is 41;000ft. and we were at 39;000ft. We started the APU and put the #1 bus on the running APU. This worked for a number of minutes; and we completed the checklist; notified Dispatch and in accordance with QRH; planned to continue to ZZZ1. The APU accomplished an auto-shutdown; and the provided power fell offline. In accordance with 737AOM; APU limitations; we attempted to start the APU again. It stayed on for about two minutes; then auto-shutdown again. We returned to the QRH and followed the APU is not available branch. This directed us to plan to land at the nearest suitable airport. At this point in the flight; the nearest suitable airport in terms of distance; time; Maintenance; and Passenger care was assessed to be ZZZ2. A divert to ZZZ2 was conducted. Looking back; I probably should have gone ahead and [requested priority handling]. No special handling was required; but had the situation turned for the worse; it would have been good to have that. If I'm solving problems with the QRH; serious consideration should be given to [requesting priority handling]. Also; to prevent landing overweight at our nearest suitable airfield; we accomplished a turn back to final to be burn a few hundred pounds of gas to be within aircraft weight limits. Consideration should have been given to accepting the slight overweight landing and follow-on inspection; in order to expedite landing. At the time; I was thinking not to further complicate an already complex situation.
Second reporter narrative
In cruise at FL390; I was the PF (Pilot Flying); Captain PM. The Master Caution started flickering on and off but too fast to actually see what it was. Over time we saw what the light was; so at XA:30 we ran the QRH for transfer bus off. We were in limits of running the APU so we turned it on and it extinguished so we thought it was the end of the procedure. We notified Dispatch that the QRH procedure had been performed and we needed fuel numbers for the running APU. Gave them current fuel on board. At XB:40 source Off light came on; same side; number one. We noticed the APU had fallen off line. We tried to start it again and for a few minutes it ran but at XC:43 fell off line again. We looked at the same procedure again for if the APU was not available and also being single electric source; we diverted to ZZZ2. Upon arrival into ZZZ2 we saw we were roughly 500 pounds heavy. On a right base; we did a right 360 turn to burn it off and we landed under weight in ZZZ2. We could have descended to a lower altitude and tried the APU a third time. Maybe next time I'll do that. We figured there could have been a bigger electric issue that was unknown. We didn't [request priority handling] and probably would next time to be safe in case we did end up losing the last good generator. Next time we could have landed overweight just to get on the ground but we didn't want to add another issue on top of the current problem.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.