Narrative:

We were being vectored off the arrival turning towards an extended 18 mile final for a visual approach; runway 16L den. Turning base leg; the ATC controller cleared us for a 'visual approach and descend to 6;000'. I repeated the clearance; the pilot flying dialed it into the FCU and selected open descent. It took about 20 seconds to recognize that 6;000 couldn't be correct since the elevation at den is at 5;500. About the time I said 'that can't be right; lets climb back up'; the pilot flying had disengaged the autopilot and had already initiated the climb. Before the sink could be arrested and a positive rate of climb established I estimate that we descended to 6;600 feet.as we climbed back to 7;000 feet; I asked the controller 'what altitude did you clear us to?'a different voice said 'the minimum sector altitude for you is 7;000.' we maintained 7;000; joined the final and landed without incident.no 'low altitude alert' was issued by ATC; nor was there any GPWS warnings emitted. We stopped the error before it became a problem.I think the time it took us both to recognize that 6;000 couldn't be a proper clearance is that both of us are east coast pilots and it is common to hear 'descend to 6;000' and 'descend to 4;000' while being vectored.I'm glad that the pilot flying briefed the field elevation and we talked about the 10;000 signals for the cabin crew during the descent phase so the field elevation was fresh in our minds. It was that in a moment of vectoring; turning; looking; talking to ATC; watching for other inbound flights; it took a moment for the error that had been made to 'sink in' and for us to take corrective action.'if you are unsure; ask' occurs on both sides of the microphone. We heard 6;000 and read back 6;000. If that wasn't correct (and it certainly wasn't) the controller didn't correct our read back.correctly stated a miscommunication problem. We shouldn't have accepted an unacceptable clearance. Approach however should have caught the error and didn't.fortunately our SOP's and training kept the problem in the minor column.

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Original NASA ASRS Text

Title: Air carrier Captain reported being cleared to descend below minimum sector altitude on a visual approach to DEN. Crew realized they were low climbed back up and landed without incident.

Narrative: We were being vectored off the arrival turning towards an extended 18 mile final for a visual approach; Runway 16L DEN. Turning base leg; the ATC controller cleared us for a 'visual approach and descend to 6;000'. I repeated the clearance; the pilot flying dialed it into the FCU and selected open descent. It took about 20 seconds to recognize that 6;000 couldn't be correct since the elevation at DEN is at 5;500. About the time I said 'that can't be right; lets climb back up'; the pilot flying had disengaged the autopilot and had already initiated the climb. Before the sink could be arrested and a positive rate of climb established I estimate that we descended to 6;600 feet.As we climbed back to 7;000 feet; I asked the controller 'what altitude did you clear us to?'A different voice said 'the minimum sector altitude for you is 7;000.' We maintained 7;000; joined the final and landed without incident.No 'low altitude alert' was issued by ATC; nor was there any GPWS warnings emitted. We stopped the error before it became a problem.I think the time it took us both to recognize that 6;000 couldn't be a proper clearance is that both of us are East Coast pilots and it is common to hear 'descend to 6;000' and 'descend to 4;000' while being vectored.I'm glad that the pilot flying briefed the field elevation and we talked about the 10;000 signals for the cabin crew during the descent phase so the field elevation was fresh in our minds. It was that in a moment of vectoring; turning; looking; talking to ATC; watching for other inbound flights; it took a moment for the error that had been made to 'sink in' and for us to take corrective action.'If you are unsure; ask' Occurs on both sides of the microphone. We heard 6;000 and read back 6;000. If that wasn't correct (and it certainly wasn't) the controller didn't correct our read back.Correctly stated a miscommunication problem. We shouldn't have accepted an unacceptable clearance. Approach however should have caught the error and didn't.Fortunately our SOP's and training kept the problem in the minor column.

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.