Date: 201712
Local time of day: 0601-1200
Location: CLT.Airport, NC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B CLT
ATC / advisory: TRACON CLT
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Distraction; Confusion; Workload
Second reporter function: First Officer
Anomaly: ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Cleared to descend via the CHSLY3 arrival into Charlotte. Initially both the First Officer and I were confused about the structure of the arrivals and whether the airplane could comply with it or not. The 737-800 did not want to do it in VNAV path; it kept falling out to speed [mode]. The Controllers changed our speed twice which made it more difficult. Speed brakes out the whole time setting each next step down. It was very complicated and distracting for both of us. I felt we were super task [saturated]. [We] switched over to Approach Control [and] they changed the runway which we had already briefed and set up for. We still were distracted with the speed brakes out; and set up for the new approach but forgot to put it in the departure arrivals section of the FMC. When being vectored for the approach things just did not look right. I asked the Approach Controller to take us out of the sequence and we would come back around for the correct approach. Charlotte Approach acted like this happens all the time. So basically outside of the final approach fix they took us out of the lineup; vectored us around; we came in and did an uneventful ILS 36 left [approach] and landing.It is my fault for not putting the new runway in the airport departures arrivals of the FMC. However I just feel this arrival is poorly constructed. I do understand they're bringing airplanes in joining the arrival underneath us but this arrival is poorly constructed. I asked Atlanta Center if other pilots complain about this arrival and they said yes. They said that Charlotte likes it and it is in the final stages of being fully approved. I just feel it is very difficult for the 737-800 to fly this approach in VNAV. It was very distracting especially when they edited our speed. The airplane just could not do the arrival; then it sets you up for other mistakes like getting a runway change when you're very busy.I just feel it is very difficult for the 737-800 to fly this approach in VNAV. In the future I will just edit the [Arrival]. [Instead] of crossing between altitudes I will just make every altitude hard which goes against the whole point of an arrival to be flown in VNAV.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported high workload and confusion on a complex RNAV arrival into CLT that led to clearance deviations.