Date: 201906
Local time of day: 1801-2400
Location: DEN.Airport, CO
Light: Daylight
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B DEN
ATC / advisory: TRACON D01
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness; Communication Breakdown
Anomaly: ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was the Captain and Pilot Flying [a flight] to DEN. Entering Denver Center; we were assigned several different arrival STARS due to thunderstorms in the DEN area. Ultimately we were vectored southwest of DEN and assigned to descend via the CREDE 3 RNAV STAR. The CREDE 3 STAR was thoroughly briefed and 11;000 feet was inserted and confirmed in the MCP altitude window with VNAV PATH confirmed. As we approached the MOGLS fix (altitude on chart is at or above 13;000 feet); DEN Approach vectored us off the STAR: they instructed us to turn 5 degrees right and descend to 11;000 feet for a left downwind to Runway 16L. My First Officer read back that exact clearance and I confirmed both the new heading and the same 11;000 feet altitude that was previously set. The Controller did not challenge the altitude readback. In hindsight; I recognize there is a possibility that both my FO and I heard and read back the wrong altitude; but neither of us think that is the case with this incident. Approximately one to two minutes later; the Approach Controller asked us to confirm that we were level at 13;000 feet MSL; and we responded that we were cleared to descend to 11;000 feet. Our approximate altitude at that time was 12;500 feet. He stated that our altitude clearance limit was 13;000 feet and instructed us to level off at 12;000 feet. From our perspective there was no additional impact on other aircraft such as TA or RA events. Once we got the altitude situation resolved; the remainder of the flight was normal and the aircraft landed uneventfully in DEN. Regarding the threat and error analysis; I did not feel like the radios were more congested or challenging than normal. Obviously; there was some sort of communication error between our Flight Crew and DEN Approach. We understood and read back an 11;000 feet altitude assignment and the Controller clearly thought he had assigned us a 13;000 feet MSL limit. I really don't know which party is at fault; but clearly communications were the root of the problem in this incident. Neither my FO nor I had any question regarding our amended clearance. If I had any doubts about the correct assigned altitude; I would have requested a clarification. I do know that if we heard the clearance wrong; we also read back the same incorrect 11;000 feet limit. Please note the Approach Controller never corrected the altitude read back unless that call was potentially blocked by another aircraft. I have had to fill out very few reports; but I pledge to be a more aggressive listener on the radios in an effort to prevent these kind of issues.




Synopsis: B737NG Captain reported overshooting the assigned altitude on the CREDE 3 RNAV STAR into DEN after misinterpreting an ATC clearance.