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B737 flight crew reported that as they started a descent; as per ATC instructions; then received a TCAS alert of traffic below.
| Attributes | |
| ACN | 1489800 |
| Time | |
| Date | 201710 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ORD.Airport |
| State Reference | IL |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Route In Use | STAR BENKY4 |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | Cessna Stationair/Turbo Stationair 6 |
| Flight Phase | Cruise |
| Person 1 | |
| Function | Captain Pilot Not Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Type 5093 |
| Person 2 | |
| Function | First Officer Pilot Flying |
| Experience | Flight Crew Type 3988 |
| Events | |
| Anomaly | ATC Issue All Types Conflict Airborne Conflict Conflict NMAC Deviation - Procedural Published Material / Policy |
| Miss Distance | Vertical 400 |
Narrative:
On the BENKY4 arrival at 9000 ft near tonie intersection; ATC gave us a clearance to descend to 8000 ft. We then received a TCAS TA 'traffic' just before descending. The TCAS traffic appeared to be on a track toward us and TCAS showed the traffic at 8500 ft. ATC did not advise us of the traffic at 8500 ft and we were cleared to descend to 8000 ft. We maintained 9000 ft due to the TCAS information and then acquired visual contact with the traffic. As the traffic passed 500 ft directly below us; TCAS responded with a RA 'monitor vertical speed'. After traffic passed; I advised ATC there was a single engine cessna that passed 500 ft below us. ATC replied something such as 'roger' or 'ok'. We then descended to 8000 ft. There were two or three other comments from other aircraft in the vicinity regarding the 8500 ft traffic including a TCAS RA that was broadcast from [another air carrier] flight. ATC then advised on frequency that there was a station air (cessna) maneuvering in the area.
Original NASA ASRS Text
Title: B737 flight crew reported that as they started a descent; as per ATC instructions; then received a TCAS alert of traffic below.
Narrative: On the BENKY4 Arrival at 9000 FT near TONIE intersection; ATC gave us a clearance to descend to 8000 FT. We then received a TCAS TA 'traffic' just before descending. The TCAS traffic appeared to be on a track toward us and TCAS showed the traffic at 8500 FT. ATC DID NOT advise us of the traffic at 8500 FT and we were cleared to descend to 8000 FT. We maintained 9000 FT due to the TCAS information and then acquired visual contact with the traffic. As the traffic passed 500 FT directly below us; TCAS responded with a RA 'monitor vertical speed'. After traffic passed; I advised ATC there was a single engine Cessna that passed 500 FT below us. ATC replied something such as 'roger' or 'ok'. We then descended to 8000 FT. There were two or three other comments from other aircraft in the vicinity regarding the 8500 FT traffic including a TCAS RA that was broadcast from [another air carrier] flight. ATC then advised on frequency that there was a Station air (Cessna) maneuvering in the area.
Data retrieved from NASA's ASRS site 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.