B737-800 Captain reported severe flight control malfunction during initial climb that required substantial manual control to maintain wings level. Flight crew returned to departure airport and landed safely.

Narrative

ZZZ to ZZZ1. CA PF (Captain Pilot Flying); less than 300 hours in type. FO PM (First Officer Pilot Monitoring); less than 100 hours at this carrier. XXX souls on board. ZZZ RWY XXR. Flaps 5 takeoff. 26K thrust. Assumed temp 39C. 150;900 lbs. ZZZZZ SID. Night. Thin cloud layer at 5000 feet. Unrestricted visibility. This was a severe flight control malfunction. What follows is my best recollection of the event. ZZZ Tower cleared us for takeoff on RWY XXR. During initial climb; at 500 feet AGL; I began a hand flown right hand turn in accordance with the ZZZZZ Departure. As I deflected the yoke to the right; it snapped forcefully right; and I experienced an extreme; uncommanded roll rate. I was struggling with both hands to stop the yoke from banking us beyond 30 degrees. The yoke was still commanding a greater roll rate. Startle factor was tremendous. I could not verbalize any words to the FO (PM). There were no master cautions; no master warnings; and no annunciator lights. Then suddenly the yoke became very light. As I moved the yoke back toward center; the extreme uncommanded roll rate kicked in to the left. I was experiencing severe longitudinal instability; and I was completely task saturated. With the instability; it was a struggle just to hold the wings level. I started making rapid commands to the FO: Bug Up Bug!" "Bug 200!" "Bug our speed!" ZZZ Departure then told us something about turning right to a fix; and contacting center. I told the FO: "No; advise ATC; flight control malfunction; present heading; 5000 feet."While climbing on the 025 heading; I continued to give left and right yoke inputs to help with troubleshooting. Somewhere between 3000 ft and 5000 ft MSL I determined I could deflect the yoke left to make a left turn and the aircraft felt normal. However; when I moved the yoke back toward center; or if I had any yoke inputs right of center; it felt like my right aileron was going straight to the full up position. Wings level felt like I was trying to balance the roll axis on a needle point. Continual yoke inputs were required to keep the wings level. What was wrong? Aileron Jam? No; there isn't any binding. Hydraulics? No; I would have an annunciator light. Bad PCU? No; the good PCU would overpower the faulty one. Feel and centering mechanism? No; left turns feel normal. I wanted the aircraft on the ground ASAP because I didn't know how much longer we could maintain positive aircraft control; any further deterioration would likely be catastrophic. While on the 025 heading and 5000 feet; ZZZ assigned a right hand turn to some heading and I told the FO "No; we can only make wide left turns." He informed ZZZ accordingly. ZZZ assigned us a left turn to heading of 270. I spun the bank angle selector to 10 degrees and began a shallow banked left hand turn. As I rollout; on heading 270; the yoke tries to overpower me again; but I anticipate it; and manage to level the wings. Nothing is improving; but it also isn't getting worse. I'm adapting; anticipating; learning how to manage this longitudinal instability and the uncommanded roll rates. On crosswind; the FO asked me if I would like him to brief the flight attendants. This question helped bring me solidly back into focus. "Yes; tell the FAs we are returning to ZZZ; Precautionary Landing; 10 mins." Why precautionary? I still had normal control of my vertical axis and lateral axis. Winds 350. Little aileron needed; if any; so I can keep firm pressure on the yoke; maintain positive control; and complete a safe landing. Then the FO asked me if I wanted him to talk to the passengers. "Yes; tell them shortly after takeoff we had a small indication up front so we are returning to ZZZ to let our maintenance team look at the aircraft. We'll provide more information on the ground." ZZZ then gave us a turn to heading 180. I share with the FO what I'm experiencing; and that I may need his help to give me more left aileron input. I asked him to notify dispatchand to include "aileron malfunction" in the text. Next; I ask the FO to look through the QRH for anything flight control and aileron related. We couldn't find anything that fit our situation. Then I have the FO complete the After Takeoff Checklist; but keep the Flaps at 5; followed by the Descent Checklist. The FO asks if I wanted him to set up and brief the approach. "Yes." Then I told him we will do Flaps 30; Autobrake 3; and to run the Before Landing Checklist. ZZZ is trying to give us a base turn. I want more distance so I have room to make a 10 degree banked turn; and to gently correct an overshoot. The FO relays to ZZZ that we want a 20 mile final. I overshoot base to final a little so we are on approximately a 340 heading to join. ZZZ asks if we can turn right at all? "No." Controller says that is okay; that he will just give us a big left hand turn so we can rejoin. I tell the FO; "No; tell him we are joining from here. We will make it work." Why? It is going to take me 6-9 minutes to make a huge left turn and I don't know how much time we have before our problem gets worse. The priority is still to get on the ground ASAP. I hit the DATA button; see 4000 ft by the fix were pointing toward; and start making commands. "Bug 180…Flaps 10…Set 4000 feet…vertical speed down 1000 fpm…arm Approach Mode." When he selected Flaps 10; the yoke started pulling left and right while the flaps were in transit; but I'm able to overpower the yoke and keep our wings level. What is going on? Flaps and ailerons are independent systems. This should not be happening. "Set 3000 feet; vertical speed down 1000 fpm…Gear down; Flaps 15" and with the Flaps 15 selection here goes the yoke oscillating left and right again. "Flaps 25…Flaps 30…Below the Line." The yoke was pulling with each flap selection. I visually verify Gear Down and Green; Flaps 30; Speed Brake Armed. We are on the Glide Slope. There will not be a go around. Something inside told me I wanted a less aggressive brake application; so around 1000 feet I tell the FO to select Autobrakes 2. With continual lateral inputs I'm able to keep the aircraft balanced on the roll axis. At approximately 20 feet Tail Strike; Tail Strike; Tail Strike is flashing on my HUD. I relax a little back pressure. Smooth touch down. Fly the nose wheel down. CA "Manual Braking." FO "Autobrakes Off." We are tracking centerline and there is a sudden jerk/pull to the right. Very odd. Like a sudden rudder kick; a grabby brake; or a right hand gust but winds are 350. I'm able to correct with brake and rudder. We slow to a near stop and clear at [taxiway] 1. Airport rescue and fire fighting asks if we require any assistance. "Tell him negative and thank you." ZZZ asks if we [are able to continue to gate]. "Yes." Ramp clears us straight in to the gate. ZZZ Ramp authorizes us to park with DGS (Docking Guidance System) only. I set the brake and we complete our shutdown flow. I tell the FO to keep the door closed. I need a minute to get myself composed. The severity of what we experienced is kicking in. I make a quick PA; "Ladies and Gentlemen; I spoke to our maintenance team and they want to take this aircraft to the hanger for troubleshooting; so please gather all of your belongings; exit the aircraft; go to the top of the jetway; and we will have further instructions. Thank you again for your patience." I had not really spoken to maintenance; but I knew the aircraft was done; and the FO and I were done. While the passengers were deplaning; I was able to finish my duties. I asked the FO to see if we had a tail strike. We did not. I called my dispatcher and he asked me if I landed overweight. This is when I was first aware that yes we landed overweight. I spoke to the Duty pilot; two local maintenance teams; and received a call from my Chief Pilot. The logbook entries took some time for me to complete; because I was trying to describe the malfunction with accurate wording; and because the aircraft maintenancelog discrepancy blocks are character limited. With 8 discrepancy entries complete; we turned the aircraft over to maintenance and went home.Reflection 1) Both pilots were needed to meet the demands of the situation. This is exactly why we must keep two pilots at the controls. I was incredibly saturated with maintaining aircraft control; and intensely thinking through the malfunction and appropriate tasks. When I gave commands to the FO; I had to trust that he was completing them exactly as I asked. I was only able to divert my attention for very brief moments to verify the big items: ILS Identifier; Gear Down and Green; Flaps 30; Speed Brakes Armed. Everything else was a bonus. The FO did a magnificent job of executing PM duties. Further; he led me with appropriate questions that helped pull me from being overwhelmed to managing the situation; and he perfectly executed PAs that are normally performed by the CA.Reflection 2) It may have been the right hand flight spoilers that were deflecting to full stop; and not an aileron problem. This would help explain why left turns were fine; but right turns were not. I don't know for certain because this fleet does not have synoptic pages.Reflection 3) After we were safely on the gate; I located two; less severe RH Aileron write ups approximately two weeks prior to this flight. If I had seen this information prior to the flight; I would have briefed it as a threat and experienced less startle factor when we experienced the severe uncommanded roll issue. Further; those write ups may also have been a flight spoiler issues but again; we pilots don't know for certain without supporting evidence from a flight control synoptic page.Cause: TBD. Unknown mechanical malfunction resulted in aircraft longitudinal instability and extreme uncommanded roll rates. Suggestions: This fleet must be equipped with system synoptic pages. Synoptic pages provide critical information to pilots during an emergency. If we had a flight control synoptic page; we would have observed exactly what was happening with our spoilers and ailerons; and responded appropriately. As it was; we were in the blind and having to guess as to what was happening with the primary and secondary flight controls. Further; the flight synoptic page would have allowed us to create more precise write ups; thus focusing the efforts of our maintenance team; and returning the aircraft to service sooner. Additionally; my three day lookback in the aircraft maintenance log didn't reveal previous RH Aileron issues. From now on; I will do a two week review of the log."