Date: 201812
Local time of day: 0001-0600
Location: ORD.Airport, IL
Light: Dusk
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: Center ZAU
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Workload; Communication Breakdown; Time Pressure
Second reporter function: Pilot Flying; 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 Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: While planning our arrival we had our routing and our STAR changed four times. On the second to last change we were cleared to a fix that did not have a crossing restriction for the initial fix; and none until several fixes later; then we were assigned to another arrival with the same initial fix; but with several restrictions. The FO (First Officer) stated that he was preparing for the most restrictive fix; set it and confirmed it and started down; we were soon notified that we descended below the initial restriction and did not need to climb again. There was no traffic conflict.High workload and changing routing and complacency regarding very similar routing with matching fixes but different altitudes. Also not setting the altitude for the nearest fix instead of the most restrictive.If ATC could remind new restrictions when a last minute routing change is made; that would help; but also; just setting the nearest restriction would do it.


Second narrative: I was the PF (Pilot Flying) as we flew to ORD. As we approached ORD; our assigned STAR changed either three or four times. We also had change of landing direction. We were overloaded while trying to set up the arrivals and brief them and a PRM approach to the east. The second to last arrival assigned was to descend via the Bradford7 arrival where there are no crossing restrictions at BDF. We were then told to descend via the Benky4 arrival and ORD was now landing west.The Benky4 arrival has a restriction to cross BDF at or above FL220. In the rush to set up the arrival and approach and get the landing data and brief; we did not notice as I descended below FL220 a few miles prior to BDF on my way to cross BYLAW between FL230 and FL190. As we arrived at BDF; ATC asked us which arrival we were assigned. We then realized that we were at approximately FL204 at BDF instead of at or above FL220. We continued to descend via and landed with no further incident. Not prioritizing the flying of the aircraft as the number one thing. I should have had the PM (Pilot Monitoring) set up the FMS and brief for me as I focused solely on flying.I will no longer set the next lower altitude on a descend via clearance until I reach the fix that I am currently approaching even when I think I have that restriction made.


Synopsis: CRJ-700 flight crew reported crossing below minimum crossing altitude on STAR due to numerous assigned STAR changes.