B737 flight crew reported they were dispatched with a single generator; and following APU failure 30 minutes after takeoff they returned to departure airport.
Synopsis
B737 flight crew reported they were dispatched with a single generator; and following APU failure 30 minutes after takeoff they returned to departure airport.
Narrative
Prior to this event; we made it to the runway and 'source' light for GEN 2 came on. We did the required check list and called Maintenance Control. They directed us to go back to the gate. After returning back to the gate; GEN 2 was deferred by MX (Maintenance) and the procedure directed us that APU generator will remain ON for the duration of the flight as 2nd source of electrical power. We push back again and took off. At cruising altitude FL350; 30 mins after take off; 'LOW OIL PRESSURE ' light came on and APU automatically shut down. We did the check list and also did the check list for having one generator. The check list directed us 'to land at the suitable airport'. I contact Dispatch and talked to Maintenance Control. They suggested to do an attempt to restart APU and if it works then we continue. Me and the FO made contingency plan; that if the APU starts then we will continue as we have suitable airports on our route in case we degrade again to single generator. And in case if APU attempt is unsuccessful then we will go back to ZZZ as it is the most suitable airport with in 30 mins. 30 mins in case we lose our single source of generator then battery time is 30 mins. The APU started; but the moment I put electrical load on it; it shut down again. We immediately decided to divert to ZZZ. We coordinated with Dispatch and ATC and start flying towards ZZZ. After all this; I talked to the Purser and give her a briefing. Then I made announcement to the passenger and told them about the situation and the decision we made to go back to ZZZ. We also requested priority handling. ATC gives us radar vectors to the visual XXL. On final approach we told Tower that we will be exiting the runway and will continue to the gate and emergency vehicles can follow us there.
Second reporter narrative
Prior to incident leg; we had a gate return due to #2 Gen Source off light that was not resettable. #2 Gen was deferred with the condition the APU Gen be utilized during the subsequent flight. Departure and climb were normal. Shortly after reaching our cruise altitude of FL350; we observed an LOW OIL PRESSURE light on the APU and a SOURCE OFF light on the #2 side. After running the QRH for both lights; the captain contacted Maintenance Control. With Maintenance Control approval he attempted to start the APU one time which resulted in an unsuccessful start. Being reliant on a single generator; we decided to advise ATC and return to ZZZ. The remainder of the flight was uneventful.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.