B737-700
Flight Crew Last 90 Days 208; Flight Crew Type 2800
Workload; Troubleshooting; Training / Qualification; Communication Breakdown; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Environment - Non Weather Related; Human Factors; Procedure
While climbing through approximately FL320 for FL350; the Captain noticed that the APU was still on and quickly reached up to turn it off. The APU was still providing electrical power to the aircraft. The main generators automatically engaged as advertised in the event of this situation. During the power disruption; the B autopilot disengaged. We had no loss to any other system on the aircraft; or displays; other than the autopilot kicking off. The Captain immediately reached over to re-engage the A autopilot and then the B autopilot and neither would engage. We then requested from ATC to level off at FL330 in order to maintain aircraft control and analyze our situation. Since the A and B autopilots worked normally on APU electrical power; the Captain made the decision to start the APU above FL250 in order to attempt to regain the autopilot system. The APU started with no problem and the Captain immediately placed the aircraft power on the APU and successfully re-engaged the B autopilot system. We then began to discuss what had just happened. We again determined that we had not lost any electrical system on the aircraft and were questioning why the A and B autopilots would not engage on normal Gen 1 and Gen 2 power. The Captain elected to leave the APU running in order to maintain maximum system reliability; for the autopilot; while operating in RVSM airspace. With the B autopilot successfully engaged; we elected to stay at FL330 and began analyzing and researching our situation by looking at the QRH Electrical System section and determined that we had no electrical system failure. We checked the circuit breaker panels and discovered no popped circuit breakers. We then began discussing RVSM operations and requirements in the event of the autopilot system falling offline. We referred to the Flight Operations Manual and the MEL section of the Electronic Flight Bag for additional information; guidance; restrictions and ATC requirements. During this review process; one of the flight attendants called and asked the Captain for a WI-FI reset (which I was not aware of). Shortly after; we received an ACARS message for a WI-FI reset followed by the 'B' Flight Attendant asking why the aft galley coffee pot was not working anymore. We immediately realized that load shedding was occurring. The Captain checked the electrical panel for aircraft power distribution and realized that we were on sole source power (the APU). Realizing our error; the Captain immediately and successfully placed the Number One GEN BUS followed by the Number Two GEN BUS online. The B autopilot momentarily disengaged during the power transfer and was immediately re-engaged. Realizing that everything was back to normal; the APU was shut down. The remainder of the flight was uneventful.So what was the sequence of events that put us into this unintentional situation? How did we both miss key items on normal flows and checklist? Our day began as day one of a three-day PM pairing. This was the first time either one of us had met or flown together. The preflight briefing and crew expectations were normal and uneventful. Our day was scheduled for two legs. Our first flight required us to return to the gate just prior to taxiing due to a passenger's dog that was barking and yelping. After the passenger; dog; and bags were removed from the aircraft we conducted a normal two-engine start; taxi; and takeoff. We landed approximately 30 minutes behind scheduled arrival time. While on the ground; we had a scheduled flight attendant crew change and requested engine oil servicing; which began to delay our turn by an additional 10 to 15 minutes. Looking back and not really realizing where we were operating with respect to the Risk and Resource Management icon; we were moving into the yellow due to the crew change waiting for Maintenance and operating in the congested alleyway between the X and X concourses.With more than 55 years of total flying experience between thetwo of us (military and civilian); we missed several checklist opportunities to correctly identify and correct improper settings for the APU and electrical panel configuration. We failed to recognize those times when the Risk and Resource Management (RRM) icon had us squarely in the yellow and at times on the border of yellow and red. Why did it happen? It certainly was not from complacency; part of the breakdown was caused by external and internal distractions along with environmental lighting conditions effect on the cockpit during the transition from sunset to night time operations during normal flow and checklist procedures. Other factors were temporary breakdowns in CRM communication by reacting too quickly before verbalizing and verifying prior to turning off the APU immediately at FL320 and by not waiting for a moment before attempting to re-engaging the A and B autopilot system after the main generators were automatically placed on line (thank you manufacturer's engineers). We also unintentionally experienced tunnel vision and partial loss of situational awareness as a crew while at FL330 during our analysis of RVSM airspace rules and options in the event that we would lose the A and B autopilot again and while analyzing why the A and B autopilot would not engage during the first attempt on the main generators. We started going down different paths and narrowed our scope while all along failing to recognize all we needed to do was place both main generators on line and attempt to re-engage the autopilots again. The rest of the pairing was back to basics and a clear understanding of applying good CRM and RRM awareness during every phase of preflight; ground; and flight operations. Realize that there are many distractions with ATC radio calls during the takeoff and climb out phases of flight. Don't pay lip service to what you expect to see; pause to really look or actually point at the switch positions. We also re-emphasized Challenge-Response-Response procedures for the checklists with special emphasis on electrical panel settings; fuel panel settings and changes; start switches; engine and wing anti-ice switches; APU operation; FMC changes; MCP; etc. Also; one of the basic lessons re-learned while maintaining aircraft control; analyzing the problem; keeping situational awareness; and coming up with a game plan; was to not be in a hurry; take the time to slow down wind the clock and take a look at the big picture in front of you. This will help you maintain situational awareness and prevent you from going down rabbit holes and getting tunnel vision.As professional pilots we are all aware of the fact that many of our procedures were derived from unintentional actions resulting in undesired consequences. I know that many people at company headquarters have put in numerous hours in developing checklist and procedures to keep the pilots of this company up to the safety and professional standards the FAA and company requires and our Customers expect.Suggested Changes: Before Taxi Checklist: Change from 'Generators Gen On/Off' Logic: Ensures verification of power source distribution for both single-engine taxi and dual engine taxi.Before Takeoff Checklist: Change from 'Number 1 Gen On/Off Number 2 Gen On/Off' Logic: Ensures verification of generator power configuration on both engines prior to take off or on one engine generator and the APU on the other side in the event of an MEL requiring that configuration.
To prevent this event from occurring again; for me as a Captain; since the first officers have been starting the engines and putting the generators online and turning the APU off; I can see that I need to create a new habit pattern. This event made it obvious to me that I consciously need to create new cues for myself with this new checklist procedure. Beginning with my next trip; I will see if I can incorporate rechecking the generators online/APU off along with the throttle advance/takeoff warning horn check.Regarding the Volant model; even though we had had several distractions and interruptions; I did not recognize that I was in the Yellow and now I can see that very clearly and will be hugely more cognizant of that in the future. I realize that checklists are 'protected airspace' and many brilliant minds have probably already been through this. My question is: Would it be better to 'anchor' attention (as we do with the flap handle when we call for the flap setting) by saying more specifically; 'Generator 1--ON; Generator 2--ON; APU--Off' versus our current 'Generators--On' cover-all response? This would also make it normal and natural whenever we were flying with an MEL of one generator inoperative and using the APU to power that bus (although that is very rare at our company with our great Maintenance). For myself; when this situation occurred; I could have been more patient in reference to getting the autopilot ON after I had self-induced the power interruption when I had turned the APU off. Thanks to our PC/PT study guides; I had remembered that this aircraft would automatically connect the generators in this circumstance; still; it was a complete shock; especially when your mind is convinced that you had already performed certain tasks earlier in the flight.
A B737-700 APU was discovered powering the aircraft at cruise; so it was turned OFF which put both engine generators online tripping the autopilot. The APU was restarted for autopilot power; but when the aircraft began load shedding both engine generators were restored for normal electrical operation.