Narrative:

Working as the controller in charge for the operation; I was over-viewing the operation on both sides of the cab. While the operation was occurring I was answering questions concerning new implemented opposite direction operation rules that have been now changed twice in two days. The approach controller was vectoring two aircraft on a left and a right downwind to the final approach course. The approach controller was dealing with an aircraft operating 10 miles out on the localizer at an altitude unfavorable for a visual approach. While deciding to re-sequence the first aircraft back around; the approach controller had issued a descent to the second aircraft with a bad read back due to what I believe was controller bias. I also did not hear the incorrect assigned altitude. The approach controller issued a descent to 130 and the pilot read back 100 and was not reissued correct altitude to maintain. The attention of the controller and myself were taken away from the aircraft on a base leg descending through 130 and instead focused on the IFR arrival and VFR target. The approach controller observed the aircraft; aircraft X descending through 124 and issued a low altitude alert and instructions to climb immediately. Aircraft X responded and reported field in sight requesting the visual approach. The approach controller issued the visual clearance to the requested runway. Aircraft X landed safely; no issues. I recommend better scan in the future and more being attentive to receiving positive read backs to control instructions. I should have limited the amount of tower distraction by pausing conversation about the new implemented rules and how they must be applied to keep the operation safe and directed my attention solely to the operation at hand.

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Original NASA ASRS Text

Title: ASE Controller reported missing read back error; resulted in aircraft descending in to a higher MVA.

Narrative: Working as the Controller in Charge for the operation; I was over-viewing the operation on both sides of the cab. While the operation was occurring I was answering questions concerning new implemented Opposite Direction Operation rules that have been now changed twice in two days. The Approach Controller was vectoring two aircraft on a left and a right downwind to the final approach course. The approach controller was dealing with an aircraft operating 10 miles out on the localizer at an altitude unfavorable for a visual approach. While deciding to re-sequence the first aircraft back around; the Approach Controller had issued a descent to the second aircraft with a bad read back due to what I believe was controller bias. I also did not hear the incorrect assigned altitude. The Approach Controller issued a descent to 130 and the pilot read back 100 and was not reissued correct altitude to maintain. The attention of the controller and myself were taken away from the aircraft on a base leg descending through 130 and instead focused on the IFR arrival and VFR target. The Approach Controller observed the aircraft; Aircraft X descending through 124 and issued a low altitude alert and instructions to climb immediately. Aircraft X responded and reported field in sight requesting the visual approach. The Approach Controller issued the visual clearance to the requested runway. Aircraft X landed safely; no issues. I recommend better scan in the future and more being attentive to receiving positive read backs to control instructions. I should have limited the amount of tower distraction by pausing conversation about the new implemented rules and how they must be applied to keep the operation safe and directed my attention solely to the operation at hand.

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.