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ARTCC supervisor reports that the rdp fdp radar was declared unreliable and controllers reverted to the darc system. The pkb low controller descended an LR31 through the altitude of a C421 because he thought he had 5 NM separation. Though the rdp was unreliable it showed only 4 NM on an n-tap. Supervisor controller questions the credibility of the n-tap when the rdp is unreliable.
| Attributes | |
| ACN | 364330 |
| Time | |
| Date | 199703 |
| Day | Thu |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : cmh |
| State Reference | OH |
| Altitude | msl bound lower : 16000 msl bound upper : 16000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zid |
| Operator | general aviation : corporate |
| Make Model Name | Learjet 31 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | descent other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | general aviation : personal |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | oversight : supervisor |
| Qualification | controller : radar |
| Experience | controller radar : 27 controller supervisory : 12 |
| ASRS Report | 364330 |
| Person 2 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| Events | |
| Anomaly | conflict : airborne less severe non adherence : required legal separation other anomaly other |
| Independent Detector | atc equipment other atc equipment : unspecified |
| Resolutory Action | none taken : anomaly accepted |
| Consequence | faa : investigated |
| Miss Distance | horizontal : 24000 vertical : 700 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error |
Narrative:
The ZID NAS rdp/fdp radar tracking program had been declared 'unreliable' and ZID was using darc/host -- a backup radar tracking program. Aircraft #1 was being descended through the altitude of aircraft #2. The radar controller 'perceived' that 5 mi separation would be present, but a subsequent investigation using the 'unreliable' NAS data ('north-tap', etc) showed only 4 mi separation. The radar controller's display (darc/host) could have been showing 5 mi while the 'unseen' NAS data could have been showing 4 mi. There is a 'credibility gap' in using 'unseen, unreliable' data as 'proof' on an operational error.
Original NASA ASRS Text
Title: ARTCC SUPVR RPTS THAT THE RDP FDP RADAR WAS DECLARED UNRELIABLE AND CTLRS REVERTED TO THE DARC SYS. THE PKB LOW CTLR DSNDED AN LR31 THROUGH THE ALT OF A C421 BECAUSE HE THOUGHT HE HAD 5 NM SEPARATION. THOUGH THE RDP WAS UNRELIABLE IT SHOWED ONLY 4 NM ON AN N-TAP. SUPVR CTLR QUESTIONS THE CREDIBILITY OF THE N-TAP WHEN THE RDP IS UNRELIABLE.
Narrative: THE ZID NAS RDP/FDP RADAR TRACKING PROGRAM HAD BEEN DECLARED 'UNRELIABLE' AND ZID WAS USING DARC/HOST -- A BACKUP RADAR TRACKING PROGRAM. ACFT #1 WAS BEING DSNDED THROUGH THE ALT OF ACFT #2. THE RADAR CTLR 'PERCEIVED' THAT 5 MI SEPARATION WOULD BE PRESENT, BUT A SUBSEQUENT INVESTIGATION USING THE 'UNRELIABLE' NAS DATA ('N-TAP', ETC) SHOWED ONLY 4 MI SEPARATION. THE RADAR CTLR'S DISPLAY (DARC/HOST) COULD HAVE BEEN SHOWING 5 MI WHILE THE 'UNSEEN' NAS DATA COULD HAVE BEEN SHOWING 4 MI. THERE IS A 'CREDIBILITY GAP' IN USING 'UNSEEN, UNRELIABLE' DATA AS 'PROOF' ON AN OPERROR.
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.