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TCASII. Flight crew followed RA of TCASII and avoided VFR traffic. ATC controller didn't alert flight crew to traffic due to overloaded traffic in sector.
| Attributes | |
| ACN | 330305 |
| Time | |
| Date | 199603 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : dtw |
| State Reference | MI |
| Altitude | msl bound lower : 18000 msl bound upper : 18500 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zob |
| Operator | common carrier : air carrier |
| Make Model Name | MD-88 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | descent other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | general aviation : personal |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other |
| Flight Plan | VFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 330305 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Events | |
| Anomaly | conflict : airborne less severe other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other flight crewa |
| Resolutory Action | flight crew : took evasive action |
| Consequence | faa : reviewed incident with flight crew |
| Miss Distance | horizontal : 4000 vertical : 700 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | other |
Narrative:
Descending into dtw, we were given a clearance direct to mizar, cross at 12000 ft. We left 20000 ft (descend now to 18000 ft, our discretion to cross mizar at 12000 ft was the clearance). At about 18500 ft we got a TCASII 'traffic' followed by 'climb, climb.' about the same time the TCASII was going off, the controller called to advise us of the traffic. We climbed back to 18500 ft (TCASII advised to 'monitor vertical speed' or something like that, and ATC told us that traffic was level at 17500 ft'). After 'clear of conflict' we resumed descent. After we landed, I called the number given to me and spoke with acting supervisor of cle area #1 and we discussed the situation. We decided that as things get busy for them, they get overloaded, and less significant things become overlooked (if something gets 'dumped' it starts with the least significant). Evidently, VFR traffic shows up differently on their display because it is less significant. My feeling is, that if they get so overloaded that they miss a possible midair, the system is trying to do too much with too little, ie, stop putting so many IFR aircraft in one sector at a time. She was overloaded with IFR aircraft and had to overlook (dump) the scan on the VFR guys.
Original NASA ASRS Text
Title: TCASII. FLC FOLLOWED RA OF TCASII AND AVOIDED VFR TFC. ATC CTLR DIDN'T ALERT FLC TO TFC DUE TO OVERLOADED TFC IN SECTOR.
Narrative: DSNDING INTO DTW, WE WERE GIVEN A CLRNC DIRECT TO MIZAR, CROSS AT 12000 FT. WE LEFT 20000 FT (DSND NOW TO 18000 FT, OUR DISCRETION TO CROSS MIZAR AT 12000 FT WAS THE CLRNC). AT ABOUT 18500 FT WE GOT A TCASII 'TFC' FOLLOWED BY 'CLB, CLB.' ABOUT THE SAME TIME THE TCASII WAS GOING OFF, THE CTLR CALLED TO ADVISE US OF THE TFC. WE CLBED BACK TO 18500 FT (TCASII ADVISED TO 'MONITOR VERT SPD' OR SOMETHING LIKE THAT, AND ATC TOLD US THAT TFC WAS LEVEL AT 17500 FT'). AFTER 'CLR OF CONFLICT' WE RESUMED DSCNT. AFTER WE LANDED, I CALLED THE NUMBER GIVEN TO ME AND SPOKE WITH ACTING SUPVR OF CLE AREA #1 AND WE DISCUSSED THE SIT. WE DECIDED THAT AS THINGS GET BUSY FOR THEM, THEY GET OVERLOADED, AND LESS SIGNIFICANT THINGS BECOME OVERLOOKED (IF SOMETHING GETS 'DUMPED' IT STARTS WITH THE LEAST SIGNIFICANT). EVIDENTLY, VFR TFC SHOWS UP DIFFERENTLY ON THEIR DISPLAY BECAUSE IT IS LESS SIGNIFICANT. MY FEELING IS, THAT IF THEY GET SO OVERLOADED THAT THEY MISS A POSSIBLE MIDAIR, THE SYS IS TRYING TO DO TOO MUCH WITH TOO LITTLE, IE, STOP PUTTING SO MANY IFR ACFT IN ONE SECTOR AT A TIME. SHE WAS OVERLOADED WITH IFR ACFT AND HAD TO OVERLOOK (DUMP) THE SCAN ON THE VFR GUYS.
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.