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ZDV center controller reported of an unsafe situation caused by the radar controller not hearing the correct readback. The aircraft descended below the minimum IFR altitude before it was corrected.
| Attributes | |
| ACN | 1396909 |
| Time | |
| Date | 201610 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZDV.ARTCC |
| State Reference | CO |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Small Transport Low Wing 2 Turbojet Eng |
| Operating Under FAR Part | Part 135 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | Flight Data / Clearance Delivery Handoff / Assist Instructor |
| Qualification | Air Traffic Control Fully Certified |
| Experience | Air Traffic Control Time Certified In Pos 1 (mon) 5 Air Traffic Control Time Certified In Pos 1 (yrs) 9 |
| Events | |
| Anomaly | ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT |
Narrative:
I was training a cpc-it on the d-side. We both heard the r-side issue a pilot's discretion descent clearance but the radios made it difficult to understand. The r-side issued a descent to 17000 in an area where the mia (minimum IFR altitude) is 16000. I thought I heard 17000 but through the statically frequency; the pilot readback 7000. The r-side initially entered 17000 in the datablock which I saw. Soon after; she entered 16000 because she told me later was because she was unsure of the read back. When the aircraft left 16200 she asked the pilot to say altitude. The pilot said we're out of 15900 for 7000. The r-side gave a low altitude alert and climbed them back to 17000. I saw mode C of 15600.if the r-side had questioned the pilot about the readback we could have prevented this. Also; if she entered 17000 in the datablock instead of 16000 it would have started to flash on the scope alerting us to the fact that the aircraft is descending. If I heard the readback more clearly I could have prevented this. The frequencies are so scratchy and statically; it makes it very hard to hear at times.
Original NASA ASRS Text
Title: ZDV Center Controller reported of an unsafe situation caused by the Radar Controller not hearing the correct readback. The aircraft descended below the minimum IFR altitude before it was corrected.
Narrative: I was training a CPC-IT on the D-side. We both heard the R-side issue a pilot's discretion descent clearance but the radios made it difficult to understand. The R-side issued a descent to 17000 in an area where the MIA (Minimum IFR Altitude) is 16000. I thought I heard 17000 but through the statically frequency; the pilot readback 7000. The R-side initially entered 17000 in the datablock which I saw. Soon after; she entered 16000 because she told me later was because she was unsure of the read back. When the aircraft left 16200 she asked the pilot to say altitude. The pilot said we're out of 15900 for 7000. The R-side gave a low altitude alert and climbed them back to 17000. I saw mode C of 15600.If the R-side had questioned the pilot about the readback we could have prevented this. Also; if she entered 17000 in the datablock instead of 16000 it would have started to flash on the scope alerting us to the fact that the aircraft is descending. If I heard the readback more clearly I could have prevented this. The frequencies are so scratchy and statically; it makes it very hard to hear at times.
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.