Date: 201403
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ; TRACON ZZZ
Aircraft component: APU
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Human factors: Communication Breakdown; Confusion; Distraction; Human-Machine Interface; Troubleshooting
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Exited Penetrated Airspace; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were at level at FL 360 in an older -300 that had three MELs. One of the MELs was a deferred APU. The other two MELs were trivial items that had no effect on the flight. I was the PM and the Captain was the PF. Without warning the autopilot disengaged; all of the Captain instruments flagged; the aft #1 fuel pump Low Pressure light illuminated; on the pitot heat panel the CAPT P/S 1 AUX STATIC; TEMP PROBE; and CAPT STATIC 1 AUX P/S lights illuminated; the yaw damper disengaged; the pressurization went to alternate mode; the cockpit mix valve became fixed in the hot position; the transponder failed and both FMCs went blank. On the First Officer's panel the only flag was on the slow/fast indicator on my ADI. After some crosschecking with the standby instruments; it was determined that my instruments were reliable and the Captain transferred the controls to me. The 'A' autopilot would not engage at all and the 'B' autopilot would engage but would just drift off while engaged; so I hand flew the airplane. We requested and descended to FL 280 for RVSM compliance and communicated our navigation issues with ATC. We both moved our seats forward and inspected the breaker panels and did not notice any breakers tripped. The Captain asked what checklist to perform in the QRH since the problem was not obvious. I told the Captain I felt we had an issue with the Bus 1. Neither the TRANSFER BUS OFF light nor the gen 1 SOURCE OFF lights were illuminated which kept throwing us off. I again asked to check the breakers and again we both looked but did not see any tripped breakers. The Captain was thumbing through the electrical section of the QRH and was not having any success finding an appropriate checklist. We talked to the flight attendants and told them what was going on and asked them to make sure that everything seemed ordinary in the back and specifically asked to see if they noticed any smoke or electrical odors. They did not notice anything unusual. To further complicate matters ZZZ Center was having some radar outages so they didn't have our transponder or primary either. So I had to provide position reports to Center as well. The Captain decided to try to talk to Maintenance Control to see if they had any recommendations. The area that we were in at the time was not good for reaching any Company stations. We tried ARINC and initially got through but it was right on a frequency boundary and we lost the patch. It took some time but the Captain was finally able to get through to Dispatch via ARINC and asked for a patch to Maintenance. We never were able to talk to Maintenance however; and by this point; we were only approximately 150 miles out of our destination and decided to scrap it and continue on; land; and worry about talking to Maintenance on the ground. Weather was clear in ZZZ but had approximately 20 knot winds. We sat the flight attendants early and advised them that without the yaw damper the tail would be swinging around more than normal. Approach Control cleared us for the visual approach and we landed Runway 26 without any issues. Upon landing; the VHF 1 radio failed and we cleared the runway and communicated with Ground Control through VHF 2. Contract Maintenance came out and embarrassed both of us when after only a few minutes he discovered the NO. 1 ALT TRANSFER BUS breaker tripped. The location of the breaker makes it incredibly hard to see while seated. The ATS call microphone and cord hide those breakers down there. Also; most people place the trash bag on the First Officer's armrest and that also hides those breakers. Although we did move the trash bag; we still never noticed the breaker. Apparently when this breaker trips the TRANSFER BUS OFF and BUS OFF lights are inhibited.


Second narrative: While I was trying to figure this out; I kept hearing ATC say to my First Officer 'primary target only' so I switched to transponder 2 and ATC then got all our information back. I write this because there seems to be some confusion on whether we were NORDO or not. I can assure you; we were not.As I dug into the QRH; I could not decipher were to start. With no direct light off to begin with; I started QRHing every light and panel. I believed that we had lost AC bus 1; but why?I then decided to involve Maintenance. I contacted ARINC and got a patch to Dispatch. On the first attempt we dropped the call; perhaps out of range. On the second attempt; we had a strong signal but somehow were again disconnected. I didn't attempt a third.... The Dispatcher later told me that Maintenance had told them; to tell us; to 'QRH the situation; do what it says; and call us on the ground.' Not exactly the response I would have expected. We continued to ZZZ and landed without incident.If I had found it [the circuit breaker]; under our new policy; I'm not sure that we would have reset it anyway. It was day VFR and the aircraft was flying fine. It wasn't really an option since I never found it. After several tests were done by Contract Maintenance; we took the same aircraft on a revenue flight.


Synopsis: When a B737-300 flight crew suffered multiple failed systems including the Captain's flight instruments they descended out of RVSM airspace and attempted to troubleshoot the problem; the multiplicity of items inoperative hindering their attempts to access an appropriate checklist.  As they were close to their destination; the airplane and their destination in the clear and communications with Dispatch and Maintenance were problematic at best they opted to concentrate on flying the airplane to a safe landing and arrival at the gate.  Once parked at the gate Contract Maintenance discovered a popped transfer bus circuit breaker which was impossible to see from either pilot position.