B737 captain reported descending below charted altitude on approach to sat when the flight crew misu...

Narrative:

We were cleared to intercept the localizer for runway 12R at sat at about 12 DME. Both the first officer and I both heard ATC state maintain at or above 2000 feet until established and cleared the ILS 12R. We were also looking for the airport as we were being vectored onto the approach; (and descending through 2500 feet) when ATC told us she had an altitude alert and we needed to maintain at or above 2800 feet; until established on the approach. I immediately disconnected the autopilot and climbed back to 2800 feet MSL. We intercepted the localizer and glideslope and the remainder of the approach and landing was uneventful. Preventative measures: I should have paid more attention to the approach chart altitude; and queried the controller when what we heard did not match with the approach chart. ATC was speaking quite fast; so if they slowed down a little; maybe we would have heard the correct altitude.

Original NASA ASRS Text

Title: B737 Captain reported descending below charted altitude on approach to SAT when the flight crew misunderstood ATC clearance.

Narrative: We were cleared to intercept the Localizer for RWY 12R at SAT at about 12 DME. Both the First Officer and I both heard ATC state maintain at or above 2000 feet until established and cleared the ILS 12R. We were also looking for the airport as we were being vectored onto the approach; (and descending through 2500 feet) when ATC told us she had an altitude alert and we needed to maintain at or above 2800 feet; until established on the approach. I immediately disconnected the autopilot and climbed back to 2800 feet MSL. We intercepted the localizer and glideslope and the remainder of the approach and landing was uneventful. Preventative Measures: I should have paid more attention to the approach chart altitude; and queried the Controller when what we heard did not match with the approach chart. ATC was speaking quite fast; so if they slowed down a little; maybe we would have heard the correct altitude.

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.

Attributes
ACN	1224847
Time
Date	201412
Local Time Of Day	1201-1800
Place
Locale Reference	SAT.Airport
State Reference	TX
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 161 Flight Crew Type 9500
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

B737 captain reported descending below charted altitude on approach to sat when the flight crew misunderstood ATC clearance.