Regional Jet 700 ER/LR (CRJ700)
Situational Awareness; Time Pressure; Workload
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance
Human Factors; Procedure
Flight to ATL. We were briefed and set up for an ILS PRM to 26L. Just after crossing ERLIN at 14000 feet on the STAR we were given new runway assignment of ILS PRM 28. We were also switched to 127.9; where we were told to descend to 12000 feet. Trying to load the transition to RWY 28 it wouldn't come up. We asked for a heading; while on an assigned heading of 160; we received a clearance to descend from 12000 feet to 7000 feet. Crossing approximately 10600 feet; ATC asked us what our assigned altitude was; Captain respond cleared to 7000; ATC came back and said climb immediately to 11000 feet. Autopilot off and GO power was set and a climb from 10400 to 11000 was accomplished. At 11000 feet autopilot was turned back on. Captain was pilot not flying; First Officer was pilot flying.Cause: Runway change last minute; having to reprogram the FMS and re-brief a new approach last minute; problems with not getting the correct transition loaded; all in an already high workload environment of the STAR.
CRJ-700 Captain reported descending below assigned altitude when they took a clearance for another aircraft. Captain mentioned workload and late runway change as contributory.