Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 107.8; Flight Crew Total 6307.75; Flight Crew Type 6307.75
Aircraft Equipment Problem Less Severe
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Shortly after takeoff As the PF I experienced intermittent failure of both roll and pitch modes (with no flags; just the disappearance and reappearance in erratic random failures of pitch and roll indications separately) of my flight director during climb through approximately 6;000 ft. Obviously the auto pilot A disconnected and I was unable to reacquire it due to the erratic nature of the problem. Communicating to my FO (First Officer) of the issue; we recognized that his flight director appeared to be operating normally. This allowed us to use autopilot B to reassess our condition. With the auto throttle on with autopilot B the Number 2 throttle advanced rapidly approximately 5 knobs forward of the Number 1 throttle and I returned it to a symmetric condition (the auto throttle disengaged itself as well; Autopilot B still was working). While bringing the throttles to an asymmetric condition to stabilize the thrust setting the Stab Trim Light illuminated; the left fuel pump light of the center tank illuminated (approximately 22;000 lbs of gas in the center tank). We requested to level off at 16;000 ft. and 250 knots and indicated to ATC that we needed a few minutes to access a condition; that we would maintain our flight plan. We executed a transfer of controls to the FO making him the PF as he also communicated with ATC. After consulting the Quick Reference Checklist; it was clear the we had multiple failures not covered by the Quick Reference Checklist. In addition; the MA lights for both Flight Directors were alternating flashing in sequence. I Acquired the appropriate enroute Airinc VHF radio frequency from the chart and phone patched both dispatch and Maintenance Control. With no solution; both Maintenance Control and Dispatch agreed with my decision to divert back to ZZZ as opposed to continuing to ZZZ1 5 hours away in mountainous terrain with automation issues at night and a potential 12 hour+ duty day. FAs (Flight Attendants) were advised; ATC was advised (Requested priority handling and equipment requested to check brakes and tires); company was advised; and an announcement was made to the pax. We used the Landing Distance Normal Configuration chart for our aircraft to obtain landing distance as Saber wouldn't calculate for us the landing performance in our overweight condition at landing (approximately 161;000 lbs). It was my judgement to forego flying for however long it would take to burn 15;000 lbs of fuel to reach landing weight; so I opted to land overweight in light of the distance required from the chart. Once ATC cleared us on a vector heading for approach to land X in ZZZ; I assumed the PF role. Landing was inconsequential and smooth exiting X; X; holding short of X on X while ZZZ Fire assessed our brakes and tires. All normal; proceeded to Gate X.
On departure out of ZZZ; the Captain experienced intermittent failure of his flight director. Both his roll and pitch command bars would randomly disappear and reappear without any warning annunciations. Autopilot A disconnected and was unable to reengage as we continued the climb. As the Captain and I began to analyze the situation; we recognized that my flight director appeared to be working normally and the Captain was able to engage Autopilot B. A short period after engaging the autopilot; the autothrottles disengaged as a result of the Number 2 throttle advancing several knob widths forward of the Number 1 throttle. The Captain returned the throttles to a symmetric condition and the autothrottles were reengaged. We had been given a climb to 16;000 ft. and decided to maintain that altitude and our current airspeed of 250 kts. as we continued our flight plan route. The Captain transferred the aircraft control to me; and I kept the radios while he further analyzed the situation and referenced the QRG. I told ATC we were working an issue but required no assistance at this time. The autothrottles once again disconnected as a result of asymmetry and we elected to keep them off for the remainder of the flight. During this time we also notice the MA light for the flight director switches was cycling back and forth from the Captain's side to the FO side. Additionally; the left center tank fuel pump LOW PRESSURE light illuminated with over 20;000 lbs. of fuel in the center tank. Lastly; the STAB OUT OF TRIM light flickered despite any changes in pitch or airspeed. It was clear that we had multiple issues not covered by the QRG; and the Captain quickly tuned the appropriate ARINC VHF radio frequency and established a phone patch with dispatch and Maintenance Control. Since there was no clear solution for our situation; dispatch and Maintenance Control agreed with the Captain's decision to divert to ZZZ as opposed to continuing. This decision was made after the Captain and I discussed the threats involved: automation issues; night landing in mountainous terrain; long duty day. The Captain advised the FAs (Flight Attendants) and made an announcement to the passengers. He then took the primary radio back from me and requested priority handling with ATC in addition to coordinating for aircraft rescue and firefighting to meet the aircraft to check our brakes and tires since we would be landing overweight. The Captain briefed the approach and calculated the landing distance using the Landing Distance Normal Configuration chart for our aircraft since Saber would not calculate at our current weight which was approximately 161;000 lbs. I agreed with the Captain's decision to land overweight; given we had the landing distance; as opposed to holding for almost 2.5 hours to burn fuel. The descent checklist was accomplished; and the Captain took over as the PF once ATC cleared us on a vector for the ILS X. A 30-flap landing was conducted and a normal landing was made. We exited on X; X; and while holding short of X; aircraft rescue and firefighting checked our brakes and tires. With an all normal; we proceeded to taxi to gate X.
B737 flight crew reported multiple systems indicating failures; resulting in the decision to execute a return to departure airport and a precautionary landing.