Narrative:

During approach to landing at msn; I was notified of a possible altitude deviation. After we landed; the tower controller requested that I call a phone number. We/I spoke to [the] manager on duty and he informed us that we descended below minimum vectoring altitude (MVA) of 4000 feet prior to receiving a visual approach clearance. He said that safety was not compromised; and there were not any traffic conflicts.the first officer was the flying pilot; autopilot engaged and I was the pm (pilot monitoring). We briefed for an ILS approach to runway 36 at msn because the wind was variable at 6kts. When we checked in with madison approach and requested runway 36 for landing we were advised to stand by to coordinate with the tower and also given a descent to 11000 feet. A few minutes later the approach controller advised us unable runway 36 due to landing traffic runway 18 and we were told to plan on radar vectors for runway 18 and cleared to descend to 4000 feet. I read the clearance to ATC as 4000 feet. Based on the assigned heading and the expectation of a visual approach clearance; I began programming the FMS for ILS/visual approach for runway 18 with presidio fix three mile right base at 3000 feet for lateral and vertical guidance. My head was down during FMS programing and I did not take note that flight control guidance was set to 3000 feet. When ATC advised us of a low altitude alert; I looked up and saw we were descending to the altitude set in pre-selector. At that moment with a high work load I did not recall the previous altitude assignment and informed ATC that we had been cleared to descend to 3000 feet. At the time I was surprised by a low altitude alert issued by ATC while we were in visual flight conditions and we immediately stopped the descent around 3200 feet. We were then instructed to climb to 3500 feet. After climbing back up we were cleared for a visual approach to runway 18. [Suggest] rigorous altitude awareness during high work load environment especially during originally briefed approach to the runway or reassigned runway.

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Original NASA ASRS Text

Title: Air Carrier flight crew reported Tower assigned 'Low Altitude' alert on final approach.

Narrative: During approach to landing at MSN; I was notified of a possible altitude deviation. After we landed; the tower controller requested that I call a phone number. We/I spoke to [the] manager on duty and he informed us that we descended below Minimum Vectoring Altitude (MVA) of 4000 feet prior to receiving a visual approach clearance. He said that safety was not compromised; and there were not any traffic conflicts.The First Officer was the flying pilot; autopilot engaged and I was the PM (pilot monitoring). We briefed for an ILS approach to runway 36 at MSN because the wind was variable at 6kts. When we checked in with Madison Approach and requested runway 36 for landing we were advised to stand by to coordinate with the Tower and also given a descent to 11000 feet. A few minutes later the approach controller advised us unable runway 36 due to landing traffic runway 18 and we were told to plan on radar vectors for runway 18 and cleared to descend to 4000 feet. I read the clearance to ATC as 4000 feet. Based on the assigned heading and the expectation of a visual approach clearance; I began programming the FMS for ILS/Visual Approach for RWY 18 with presidio fix three mile right base at 3000 feet for lateral and vertical guidance. My head was down during FMS programing and I did not take note that flight control guidance was set to 3000 feet. When ATC advised us of a low altitude alert; I looked up and saw we were descending to the altitude set in pre-selector. At that moment with a high work load I did not recall the previous altitude assignment and informed ATC that we had been cleared to descend to 3000 feet. At the time I was surprised by a low altitude alert issued by ATC while we were in visual flight conditions and we immediately stopped the descent around 3200 feet. We were then instructed to climb to 3500 feet. After climbing back up we were cleared for a visual approach to runway 18. [Suggest] rigorous altitude awareness during high work load environment especially during originally briefed approach to the runway or reassigned runway.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.