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Small aircraft Y unauthorized descent to occupied altitude had less than standard separation from small transport X. Pilot deviation. System error.
| Attributes | |
| ACN | 250592 |
| Time | |
| Date | 199309 |
| Day | Wed |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : cgx |
| State Reference | IL |
| Altitude | msl bound lower : 2500 msl bound upper : 3200 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : ord |
| Make Model Name | Small Transport, Low Wing, 2 Recip Eng |
| Flight Phase | cruise other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | Small Aircraft, Low Wing, 1 Eng, Fixed Gear |
| Flight Phase | descent other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : approach |
| Qualification | controller : radar |
| ASRS Report | 250592 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : single pilot |
| Qualification | pilot : instrument pilot : commercial |
| Events | |
| Anomaly | altitude deviation : overshoot conflict : airborne less severe non adherence : published procedure non adherence : clearance non adherence : required legal separation |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | Other |
| Miss Distance | horizontal : 6000 vertical : 700 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error Pilot Deviation |
Narrative:
Small transport X is on 040 degree heading at 4000 ft. Small aircraft Y is descended to 4000 ft on 360 degree heading. Both aircraft are being vectored to VFR tower controled airport (chicago meigs). Small aircraft Y mode C is not working or intermittent at best. Small transport X is descended to 3000 ft. Small aircraft Y altitude is checked and he is leaving 5200 ft. Small transport X is told to expedite descent to 3000 ft. Small aircraft Y reads back descend to 3000 ft. (I, as the controller, do not copy this readback until hearing the tape later.) I later clear small transport X to 2500 ft. Small aircraft Y is descended from 4000 ft to 3000 ft when I notice his mode C showed 3300 ft for 1 sweep so I question his altitude. Pilot says he is leaving 3200 ft for 3000 ft. I climb him back to 4000 ft and descend small transport X to 2000 ft.
Original NASA ASRS Text
Title: SMA Y UNAUTH DSCNT TO OCCUPIED ALT HAD LTSS FROM SMT X. PLTDEV. SYS ERROR.
Narrative: SMT X IS ON 040 DEG HDG AT 4000 FT. SMA Y IS DSNDED TO 4000 FT ON 360 DEG HDG. BOTH ACFT ARE BEING VECTORED TO VFR TWR CTLED ARPT (CHICAGO MEIGS). SMA Y MODE C IS NOT WORKING OR INTERMITTENT AT BEST. SMT X IS DSNDED TO 3000 FT. SMA Y ALT IS CHKED AND HE IS LEAVING 5200 FT. SMT X IS TOLD TO EXPEDITE DSCNT TO 3000 FT. SMA Y READS BACK DSND TO 3000 FT. (I, AS THE CTLR, DO NOT COPY THIS READBACK UNTIL HEARING THE TAPE LATER.) I LATER CLR SMT X TO 2500 FT. SMA Y IS DSNDED FROM 4000 FT TO 3000 FT WHEN I NOTICE HIS MODE C SHOWED 3300 FT FOR 1 SWEEP SO I QUESTION HIS ALT. PLT SAYS HE IS LEAVING 3200 FT FOR 3000 FT. I CLB HIM BACK TO 4000 FT AND DSND SMT X TO 2000 FT.
Data retrieved from NASA's ASRS site as of July 2007 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.