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ZMA controller reported he thought an aircraft was descending based on a mode C readout and descended another aircraft based on that mode C. The first aircraft was not descending and separation was lost.
| Attributes | |
| ACN | 934487 |
| Time | |
| Date | 201102 |
| Local Time Of Day | 0001-0600 |
| Place | |
| Locale Reference | ZMA.ARTCC |
| State Reference | FL |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | M-20 G Statesman |
| Flight Phase | Descent |
| Route In Use | None |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | PA-32 Cherokee Six/Lance/Saratoga/6X |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Cruise |
| Route In Use | None |
| Flight Plan | IFR |
| Person 1 | |
| Function | Enroute |
| Qualification | Air Traffic Control Fully Certified |
| Events | |
| Anomaly | ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy |
| Miss Distance | Horizontal 18000 Vertical 800 |
Narrative:
Aircraft 'a' had been given a crossing restriction to cross 10 miles east of xyz at 4;000 ft. Aircraft 'B' was level at 7;000 ft and needed to cross abcde at 4;000 ft. I noticed the mode C of aircraft 'a' at 059 and thought that he'd begun his descent. I then issued aircraft 'B' a descent clearance to 6;000 ft since aircraft 'a' had vacated that altitude. However; the mode C of aircraft 'a' remained at 059. The pilot had not started down after all. When conflict alert activated; I issued 20 degree turns to both aircraft; but separation had already been lost. [Do] not descend one aircraft into another.
Original NASA ASRS Text
Title: ZMA Controller reported he thought an aircraft was descending based on a mode C readout and descended another aircraft based on that mode C. The first aircraft was not descending and separation was lost.
Narrative: Aircraft 'A' had been given a crossing restriction to cross 10 miles east of XYZ at 4;000 FT. Aircraft 'B' was level at 7;000 FT and needed to cross ABCDE at 4;000 FT. I noticed the mode C of aircraft 'A' at 059 and thought that he'd begun his descent. I then issued aircraft 'B' a descent clearance to 6;000 FT since aircraft 'A' had vacated that altitude. However; the mode C of aircraft 'A' remained at 059. The pilot had not started down after all. When conflict alert activated; I issued 20 degree turns to both aircraft; but separation had already been lost. [Do] not descend one aircraft into another.
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.