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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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TCASII RA. Due to faulty mode C in intruder aircraft, reporter's TCASII gave a descent command. When reporter flight crew reported descent to departure controller, they were advised of the other aircraft's altitude and it had a faulty mode C. Because of the faulty warning, the reporter flight crew was actually descending into the other aircraft resulting in a near midair collision.
| Attributes | |
| ACN | 336700 |
| Time | |
| Date | 199605 |
| Day | Sat |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : mdw |
| State Reference | IL |
| Altitude | msl bound lower : 5500 msl bound upper : 6000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : ord |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | Brasilia EMB-120 All Series |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp pilot : instrument |
| Experience | flight time last 90 days : 225 flight time total : 12000 flight time type : 2500 |
| ASRS Report | 336700 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other flight crewa |
| Resolutory Action | flight crew : took evasive action |
| Consequence | Other |
| Miss Distance | horizontal : 0 vertical : 500 |
| Supplementary | |
| Primary Problem | Aircraft |
Narrative:
Level at 6000 ft, radar vector, TCASII RA 'descend.'saw aircraft at about 1:30 O'clock about 3 mi, appeared below us. We descended and advised ATC of RA. At 5500 ft traffic still appeared below us, got 'clear of traffic.' returned to 6000 ft. ATC advised that other aircraft (brasilia) was in fact level at 5000 ft but its C mode was malfunctioning, indicating it was at 6200 ft. (Initially the TCASII display showed intruder above us slightly.) this was one occasion when adhering to a TCASII RA could have created a mishap.
Original NASA ASRS Text
Title: TCASII RA. DUE TO FAULTY MODE C IN INTRUDER ACFT, RPTR'S TCASII GAVE A DSCNT COMMAND. WHEN RPTR FLC RPTED DSCNT TO DEP CTLR, THEY WERE ADVISED OF THE OTHER ACFT'S ALT AND IT HAD A FAULTY MODE C. BECAUSE OF THE FAULTY WARNING, THE RPTR FLC WAS ACTUALLY DSNDING INTO THE OTHER ACFT RESULTING IN A NMAC.
Narrative: LEVEL AT 6000 FT, RADAR VECTOR, TCASII RA 'DSND.'SAW ACFT AT ABOUT 1:30 O'CLOCK ABOUT 3 MI, APPEARED BELOW US. WE DSNDED AND ADVISED ATC OF RA. AT 5500 FT TFC STILL APPEARED BELOW US, GOT 'CLR OF TFC.' RETURNED TO 6000 FT. ATC ADVISED THAT OTHER ACFT (BRASILIA) WAS IN FACT LEVEL AT 5000 FT BUT ITS C MODE WAS MALFUNCTIONING, INDICATING IT WAS AT 6200 FT. (INITIALLY THE TCASII DISPLAY SHOWED INTRUDER ABOVE US SLIGHTLY.) THIS WAS ONE OCCASION WHEN ADHERING TO A TCASII RA COULD HAVE CREATED A MISHAP.
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.