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A center controller reported an aircraft descended below its assigned altitude and below the minimim IFR altitude.
| Attributes | |
| ACN | 1736004 |
| Time | |
| Date | 202003 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZLC.ARTCC |
| State Reference | UT |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Citation Excel (C560XL) |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Descent |
| Route In Use | Other RNAV GPS Apch |
| Flight Plan | IFR |
| Person 1 | |
| Function | Enroute |
| Qualification | Air Traffic Control Fully Certified |
| Experience | Air Traffic Control Time Certified In Pos 1 (yrs) 7 |
| Events | |
| Anomaly | Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT |
Narrative:
Aircraft X was descending for an arrival into a non towered airport. I had elected to vector aircraft X north of the IAF for a straight in approach. Aircraft X descended with the terrain as instructed until entering a 13;000 ft. Mia (minimum IFR altitude) box. At that point aircraft X was cleared direct the IAF. After aircraft X was cleared direct the IAF; I cleared the aircraft to cross the initial approach fix at or above 13;000 ft. For the straight in RNAV approach. The pilot read back the clearance and left out the straight in command. I restated the straight in portion of the clearance to the pilot and he read back the straight in portion of the clearance correctly.I attended to a few other duties before switching the aircraft to CTAF. As I returned to switch aircraft X to the CTAF I noticed the aircraft had descended below 13;000 ft. To 11;800 ft. I restated the clearance to verify that the pilot was to cross the IAF at 13;000 ft.; then issued a low altitude alert for the area mia the pilot was in. At that point the pilot was in the lowest mia in that area of 12;000 ft. The aircraft had descended to 11;200 ft. Before I read the low altitude alert because it took me a few seconds to bring up my mia chart and verify that he wasn't on the approach already as well as in the 12;000 ft. Mia box. When advising the aircraft of the low altitude alert the pilot responded that they were currently on a visual approach. I verified with the pilot of aircraft X that the airport was in sight. The pilot confirmed airport in sight; and that is when I cleared the pilot for the visual approach. I advised my supervisor of the incident immediately after the visual approach clearance was given.
Original NASA ASRS Text
Title: A Center Controller reported an aircraft descended below its assigned altitude and below the Minimim IFR Altitude.
Narrative: Aircraft X was descending for an arrival into a non towered airport. I had elected to vector Aircraft X north of the IAF for a straight in approach. Aircraft X descended with the terrain as instructed until entering a 13;000 ft. MIA (Minimum IFR Altitude) box. At that point Aircraft X was cleared direct the IAF. After Aircraft X was cleared direct the IAF; I cleared the aircraft to cross the initial approach fix at or above 13;000 ft. for the straight in RNAV Approach. The Pilot read back the clearance and left out the straight in command. I restated the straight in portion of the clearance to the Pilot and he read back the straight in portion of the clearance correctly.I attended to a few other duties before switching the aircraft to CTAF. As I returned to switch Aircraft X to the CTAF I noticed the aircraft had descended below 13;000 ft. to 11;800 ft. I restated the clearance to verify that the Pilot was to cross the IAF at 13;000 ft.; then issued a low altitude alert for the area MIA the Pilot was in. At that point the Pilot was in the lowest MIA in that area of 12;000 ft. The aircraft had descended to 11;200 ft. before I read the low altitude alert because it took me a few seconds to bring up my MIA chart and verify that he wasn't on the approach already as well as in the 12;000 ft. MIA box. When advising the aircraft of the low altitude alert the Pilot responded that they were currently on a visual approach. I verified with the Pilot of Aircraft X that the airport was in sight. The pilot confirmed airport in sight; and that is when I cleared the Pilot for the visual approach. I advised my Supervisor of the incident immediately after the visual approach clearance was given.
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.