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Less than standard separation when descending air carrier X receives TCASII and stops descent at same altitude of air carrier Y. Reporter had projected the descending aircraft to be ahead and below the conflicting traffic. Operational error.
| Attributes | |
| ACN | 335875 |
| Time | |
| Date | 199605 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : ape |
| State Reference | OH |
| Altitude | msl bound lower : 16000 msl bound upper : 16000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zid |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent other |
| Route In Use | arrival other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| Experience | controller radar : 19 |
| ASRS Report | 335875 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | non adherence : published procedure non adherence : required legal separation other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified |
| Resolutory Action | none taken : detected after the fact |
| Consequence | Other |
| Miss Distance | horizontal : 22800 vertical : 0 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error |
Narrative:
Air carrier X en route to cmh descending to 11000 ft, stopped his descent at 16000 ft because he saw traffic below him on TCASII. #2 aircraft was air carrier Y wbound to rod VOR and beyond. (Just south of V72). I was the radar controller of the rod (rosewood) sector, low altitude, at the time of this incident. The sector was moderately busy or better with traffic (15 plus aircraft). 5 mins prior to conflict, air carrier X stepped down to 17000 ft because of air carrier Y at 16000 ft. 2-3 mins later upon a scan of his descent progress, I cleared air carrier X to 11000 ft. At this time air carrier X was at about 19000 ft which told me he had a good rate of descent going which would allow him to vacate 15000 ft prior to air carrier Y's airspace, also, upper winds were from the northwest which gave air carrier X a ground speed of 510 KTS which projected him to be ahead of air carrier Y's projected point of conflict by more than 5 mi. At around XX43 I observed the conflict alert blink, seeing both aircraft at 16000 ft 4.75 mi apart. I turned air carrier Y right 20 degrees and asked air carrier X to verify his altitude because my estimate of his previous rate should have had him 14000 ft or lower. Air carrier X said he was at 16000 ft because TCASII had indicated traffic and so he stopped descending. I believe my initial assessment of his rate gave me time to issue his descent to 11000 ft. Why he slowed his rate? He didn't advise, he didn't say he was leveling either. There was no WX or chop. The frequency was busy but had he continued at even 1500 FPM rate, I think he would have been 1000 ft or more below the traffic. He, air carrier X, said had I issued traffic ahead of time, would have helped and I agree this could have been useful but due to traffic volume I didn't this time. If descent/climb rate, speed change significantly we should be advised.
Original NASA ASRS Text
Title: LTSS WHEN DSNDING ACR X RECEIVES TCASII AND STOPS DSCNT AT SAME ALT OF ACR Y. RPTR HAD PROJECTED THE DSNDING ACFT TO BE AHEAD AND BELOW THE CONFLICTING TFC. OPERROR.
Narrative: ACR X ENRTE TO CMH DSNDING TO 11000 FT, STOPPED HIS DSCNT AT 16000 FT BECAUSE HE SAW TFC BELOW HIM ON TCASII. #2 ACFT WAS ACR Y WBOUND TO ROD VOR AND BEYOND. (JUST S OF V72). I WAS THE RADAR CTLR OF THE ROD (ROSEWOOD) SECTOR, LOW ALT, AT THE TIME OF THIS INCIDENT. THE SECTOR WAS MODERATELY BUSY OR BETTER WITH TFC (15 PLUS ACFT). 5 MINS PRIOR TO CONFLICT, ACR X STEPPED DOWN TO 17000 FT BECAUSE OF ACR Y AT 16000 FT. 2-3 MINS LATER UPON A SCAN OF HIS DSCNT PROGRESS, I CLRED ACR X TO 11000 FT. AT THIS TIME ACR X WAS AT ABOUT 19000 FT WHICH TOLD ME HE HAD A GOOD RATE OF DSCNT GOING WHICH WOULD ALLOW HIM TO VACATE 15000 FT PRIOR TO ACR Y'S AIRSPACE, ALSO, UPPER WINDS WERE FROM THE NW WHICH GAVE ACR X A GND SPD OF 510 KTS WHICH PROJECTED HIM TO BE AHEAD OF ACR Y'S PROJECTED POINT OF CONFLICT BY MORE THAN 5 MI. AT AROUND XX43 I OBSERVED THE CONFLICT ALERT BLINK, SEEING BOTH ACFT AT 16000 FT 4.75 MI APART. I TURNED ACR Y R 20 DEGS AND ASKED ACR X TO VERIFY HIS ALT BECAUSE MY ESTIMATE OF HIS PREVIOUS RATE SHOULD HAVE HAD HIM 14000 FT OR LOWER. ACR X SAID HE WAS AT 16000 FT BECAUSE TCASII HAD INDICATED TFC AND SO HE STOPPED DSNDING. I BELIEVE MY INITIAL ASSESSMENT OF HIS RATE GAVE ME TIME TO ISSUE HIS DSCNT TO 11000 FT. WHY HE SLOWED HIS RATE? HE DIDN'T ADVISE, HE DIDN'T SAY HE WAS LEVELING EITHER. THERE WAS NO WX OR CHOP. THE FREQ WAS BUSY BUT HAD HE CONTINUED AT EVEN 1500 FPM RATE, I THINK HE WOULD HAVE BEEN 1000 FT OR MORE BELOW THE TFC. HE, ACR X, SAID HAD I ISSUED TFC AHEAD OF TIME, WOULD HAVE HELPED AND I AGREE THIS COULD HAVE BEEN USEFUL BUT DUE TO TFC VOLUME I DIDN'T THIS TIME. IF DSCNT/CLB RATE, SPD CHANGE SIGNIFICANTLY WE SHOULD BE ADVISED.
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.