Date: 202008
Local time of day: 0601-1200
Location: IAH.Airport, TX
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent; Initial Approach
Airspace: Class B IAH
ATC / advisory: TRACON I90
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Human-Machine Interface; Workload
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation - Altitude Overshoot; 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 Became Reoriented
Contributing factors: Human Factors; Procedure; Chart Or Publication
Primary problem: Procedure

Narrative: We anticipated Runway 26R arriving from the north as is common at IAH. We were cleared to descend via DRLLR 5 and direct MPORT and set the bottom altitude to 6000' as indicated on STAR. Inside DRLLR; approach told us to change to 26L. Pilot Flying (PF) update the FMC to 26L. The only difference between the arrivals are the name of the last point and its altitude (26L is 1;000; higher). PF or Pilot Monitoring (PM) both missed the need to adjust the open descent altitude from 6;000' (26R) to 7;000 (26L). Descending through 7;000' PM called '7;000 for 6;000'.  PF rechecked the STAR chart and noticed the discrepancy and adjusted the flight path to level at 7;000'. Aircraft in fact descended below 7;000' and crew immediately notified ATC.The late notification of the runway change and essentially the only difference in the arrivals being the last point may have led to thinking it was an uncomplicated change. Additionally PM was on first flight in nearly 15 weeks.Suggestions reconfirming the correct altitude set in altitude window.


Second narrative: Descending into IAH on the DRLLR5 arrival. Captain Pilot Flying (PF). On initial contact with approach we were assigned runway 26R. Performed an arrival briefing; including STAR altitudes per SOP.  Cleared to descend via. Set 6000 ft. in the altitude window as the bottom of the arrival. Deviated around some weather while on the arrival. Subsequent controller switches us to Runway 26L. Switch runways in the FMC; brief and verify the approach.Approaching ZOEEE intersection at 7000' and 210 KIAS; when we realize that the subsequent waypoint SKLER is no longer on the flight plan. Looking at the chart we realize that the arrival ends at ZOEEE for runway 26L. By then; aircraft had initiated a descent. Stopped the descent at approximately 6500 feet and returned to 7000 feet. Informed ATC; who told us not to worry about it and cleared us down to 5000 feet. Continued the arrival and approach to a normal landingI should have checked more thoroughly for changes to the Arrival after the runway change. There are small notes in parenthesis after each arrival fix indicating which runway they apply to. During the higher than normal workload; I missed those. It would have been useful if those notes would have been identified a little bit more prominently on the chart.


Synopsis: Flight crew reported descending below the charted altitude while on the STAR; which they attributed to a late runway change and similar procedures.