Date: 201507
Local time of day: 1801-2400
Location: ZTL.ARTCC, GA
Flight conditions: VMC
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZTL
ATC / advisory: Center ZTL
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Fatigue
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Originally set at Houston gate X. We were set to push off of gate X approximately 34 minutes late at XA:33Z due to aft lavatory being cleaned and placarded inoperative. Once we pushed; I closed the APU valve for engine start; turned off the packs; and then tried to reopen the APU valve; to start engines. The APU valve would not open and was failed closed. After numerous attempts to recycle; consulting the QRH; and talking on the radio with maintenance; it was evident that maintenance was going to have to look at the valve and we would need to return to the gate. At this point it was getting extremely hot in the aircraft due to an inability to cool the aircraft because the APU valve had failed in the closed position. The temperature throughout the cockpit and cabin was over 90 degrees at this time. We called ramp and told them that we would be returning to gate X. Ramp then told us to confirm with Operations. Operations then denied us a return to gate X; even though it was abeam the aircraft. Operations cited an international arrival as the priority for gate X. The Captain tried to intervene and express his concern for passenger comfort with the temperature in the aircraft becoming more than uncomfortable and approaching unbearable. The Captain had concerns that the heat stress was unbearable for the passengers because at this point the aircraft was indicating a temperature of over 95 Degrees. Operations continued to insist that the priority for gate X was the international arrival. Operations then directed us to be towed to Gate Y. The Captain then relayed to the tug driver that we needed to be towed to Gate Y. The tug driver then refused to take the aircraft to Gate Y; citing that it was too far of a tow. The Captain then notified Operation of the situation to which Operations then coordinated for the supertug to meet us at the aircraft and get towed to gate Y. At this point the temperature was over 98 degrees. The Captain tried one last time to voice his concerns of passenger discomfort and fear of heat stress to Operations; to which; operations still directed us to go to gate Y. Once we were towed to gate Y; there was no jet-way driver there; thus causing further delay and more heat stress. Finally; we blocked in at XB:05Z. The Captain then elected to deplane the passengers in an effort to cool down the cabin and the passengers while maintenance worked the issue.After; a lengthy delay cooling down the aircraft; maintenance placarded the APU and properly annotated it in the logbook. The aircraft was reboarded and we pushed at XD:01Z. At this point the Captain was approaching his max duty day and approaching a Crew Critical Offtime (CCO) time of XD:32. The Captain accepted a CCO extension of 2 hours. We then departed at XD:25Z.After leveling off at FL370; approximately at XE:50Z; the left generator appeared to be offline; the switch was not depressed and the flow valve indication appeared to have no flow line; leading one to think that the left generator was offline. Due to this fact; the Captain inadvertently tripped the left generator due to its faulty indication. The generator then came offline as well as both utility buses were shed momentarily. The left generator and both utility buses were then immediately restored. No undesired aircraft state or overall safety of the flight was compromised as a result of this inadvertent trip of the left generator. Max duty day fatigue along with the extreme heat stress contributed to the Captain's inadvertent trip of the left generator. The QRH was then referenced to ensure that all items that resulted from this action were appropriately taken care of.




Synopsis: B757 FO reported the Captain inadvertently disconnected the left generator in flight following an extended ground delay in extreme heat.