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S56 TRACON controller reported aircraft descended below clearance altitude and entered a higher MVA.
| Attributes | |
| ACN | 1600235 |
| Time | |
| Date | 201812 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | S56.TRACON |
| State Reference | UT |
| Aircraft 1 | |
| Make Model Name | Medium Large Transport Low Wing 2 Turbojet Eng |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | Approach |
| Qualification | Air Traffic Control Fully Certified |
| Events | |
| Anomaly | Deviation - Altitude Overshoot Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT |
Narrative:
Aircraft X was in the downwind at 110. My instructions were 'reduce speed to one eight zero then descend and maintain nine thousand.' aircraft X read back the clearance correctly. I later observed aircraft X at 082 and assigned 085 to meet the MVA requirement. Aircraft X climbed back up to 085. Separation with terrain was lost. I should have noticed the incorrect altitude sooner. Aircraft X was 800 feet below their assigned altitude before I noticed it and took action. I also did not issue a safety alert. Although in my opinion 080 is not an unsafe altitude with terrain in this area; there are other factors such as mountain wave and canyon winds that could cause additional safety risks for the aircraft. I do not know what could have been done in the cockpit to prevent the event. Perhaps if they were unsure of the altitude assignment; they could have requested that I verify the altitude assignment.
Original NASA ASRS Text
Title: S56 TRACON Controller reported aircraft descended below clearance altitude and entered a higher MVA.
Narrative: Aircraft X was in the downwind at 110. My instructions were 'Reduce speed to one eight zero then descend and maintain nine thousand.' Aircraft X read back the clearance correctly. I later observed Aircraft X at 082 and assigned 085 to meet the MVA requirement. Aircraft X climbed back up to 085. Separation with terrain was lost. I should have noticed the incorrect altitude sooner. Aircraft X was 800 feet below their assigned altitude before I noticed it and took action. I also did not issue a safety alert. Although in my opinion 080 is not an unsafe altitude with terrain in this area; there are other factors such as mountain wave and canyon winds that could cause additional safety risks for the aircraft. I do not know what could have been done in the cockpit to prevent the event. Perhaps if they were unsure of the altitude assignment; they could have requested that I verify the altitude assignment.
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.