Narrative:

After landing; tower gave us center phone number for a possible pilot deviation. Center stated we had descended from 12;000 ft to 10;000 ft without proper clearance. Here are the facts of the event. Flying the arrival; center subsequently cleared us directly to airport; maintain 12;000 ft. I acknowledged and we complied. During the frequency change to approach control; I called on 124.95 with our descent clearance to 12;000 ft. Although the radio was scratchy; both the first officer and I thought we heard a descent clearance to 10;000 ft. I responded with our descent to 'one zero thousand.' I then responded to approach control to expect vector for a visual approach to runway 20. After that; approach control frequency became extremely scratchy and weak. I called approach control stated he was unreadable. After a call in-the-blind. I switched to chart frequency 132.02. Checking in with approach control on 132.02 (descending through approximately 11;700 ft); the controller asked us our assigned altitude. I told him 10;000 ft. There was no further discussion concerning our descent to 10;000 ft with approach control. The approach and landing was uneventful. I now realize the correct; initial frequency for approach control was 124.97. My thinking is that there must have been some bleed-through from 124.97 to 124.95. I very much regret the events of this situation. Again; I must emphasize both the first officer and I thought we heard a clearance to 10;000 ft; and that we believed we very properly complying with instructions and procedures. During my phone call with center; he told me there was no loss of separation.

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Original NASA ASRS Text

Title: A MD80 flight crew mistakenly tuned an incorrect approach frequency and thought they heard a descent clearance. Following a period of silence; the correct frequency was selected and the crew was told of their incorrect descent and possible deviation.

Narrative: After landing; Tower gave us Center phone number for a possible pilot deviation. Center stated we had descended from 12;000 FT to 10;000 FT without proper clearance. Here are the facts of the event. Flying the Arrival; Center subsequently cleared us directly to Airport; maintain 12;000 FT. I acknowledged and we complied. During the frequency change to Approach Control; I called on 124.95 with our descent clearance to 12;000 FT. Although the radio was scratchy; both the First Officer and I thought we heard a descent clearance to 10;000 FT. I responded with our descent to 'one zero thousand.' I then responded to Approach Control to expect vector for a visual approach to Runway 20. After that; Approach Control frequency became extremely scratchy and weak. I called Approach Control stated he was unreadable. After a call in-the-blind. I switched to chart frequency 132.02. Checking in with Approach Control on 132.02 (descending through approximately 11;700 FT); The Controller asked us our assigned altitude. I told him 10;000 FT. There was no further discussion concerning our descent to 10;000 FT with Approach Control. The approach and landing was uneventful. I now realize the correct; initial frequency for Approach Control was 124.97. My thinking is that there must have been some bleed-through from 124.97 to 124.95. I very much regret the events of this situation. Again; I must emphasize both the First Officer and I thought we heard a clearance to 10;000 FT; and that we believed we very properly complying with instructions and procedures. During my phone call with Center; he told me there was no loss of separation.

Data retrieved from NASA's ASRS site as of April 2012 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.