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Departure controller climbing 2 air carrier MD80's on westerly vectors, with the second MD80 maintaining visual separation from the first MD80. The first MD80 descended to within 100 ft of the second aircraft while responding to a TCASII alert. Near midair collision occurred even though the first aircraft was advised of the visual separation in use.
| Attributes | |
| ACN | 379077 |
| Time | |
| Date | 199709 |
| Day | Thu |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : dfw |
| State Reference | TX |
| Altitude | msl bound lower : 9000 msl bound upper : 9000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : dfw |
| Operator | common carrier : air carrier |
| Make Model Name | MD-80 Series (DC-9-80) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | climbout : intermediate altitude descent other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | MD-80 Series (DC-9-80) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | climbout : intermediate altitude cruise other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : departure |
| Qualification | controller : radar pilot : private |
| Experience | controller military : 4 controller radar : 13 flight time total : 135 |
| ASRS Report | 379077 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | conflict : nmac non adherence : required legal separation non adherence : clearance other anomaly other |
| Independent Detector | atc equipment other atc equipment : unspecified aircraft equipment other aircraft equipment : unspecified other controllera |
| Resolutory Action | flight crew : took evasive action other |
| Consequence | Other |
| Miss Distance | horizontal : 0 vertical : 100 |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
Narrative:
Aircraft #1 departed runway 17R at dfw and approximately 6 mi south of the airport was assigned a wbound heading. Approximately 3 mi in trail of aircraft #1, aircraft #2 departed dfw sbound. Aircraft #2 reported aircraft #1 in sight and was instructed to maintain visual separation, maintain 9000 ft, and to turn right heading 270 degrees. Aircraft #1 was advised of aircraft #2's visual separation and was climbing from 8500 ft to 17000 ft. When aircraft #2 leveled at 9000 ft, aircraft #1 was observed climbing from 9500 ft. Aircraft #1 then advised that he was following a TCASII RA and descending from 9500 ft. Aircraft #1 descended to 9100 ft over aircraft #2 at 9000 ft. To prevent recurrence: TCASII is an excellent tool when utilized appropriately. The conflict comes when defining 'appropriate utilization.' it appears logical to most controllers that when ATC instructions are issued (as in this situation) to prevent a collision, pilots should follow assigned instructions rather than TCASII RA's. I also understand the design of TCASII to provide safety when ATC instructions are inadequate. This situation confirms the theory that TCASII RA's must be a 'second' line of defense and should not be allowed to take precedence over ATC instructions.
Original NASA ASRS Text
Title: DEP CTLR CLBING 2 ACR MD80'S ON WESTERLY VECTORS, WITH THE SECOND MD80 MAINTAINING VISUAL SEPARATION FROM THE FIRST MD80. THE FIRST MD80 DSNDED TO WITHIN 100 FT OF THE SECOND ACFT WHILE RESPONDING TO A TCASII ALERT. NMAC OCCURRED EVEN THOUGH THE FIRST ACFT WAS ADVISED OF THE VISUAL SEPARATION IN USE.
Narrative: ACFT #1 DEPARTED RWY 17R AT DFW AND APPROX 6 MI S OF THE ARPT WAS ASSIGNED A WBOUND HDG. APPROX 3 MI IN TRAIL OF ACFT #1, ACFT #2 DEPARTED DFW SBOUND. ACFT #2 RPTED ACFT #1 IN SIGHT AND WAS INSTRUCTED TO MAINTAIN VISUAL SEPARATION, MAINTAIN 9000 FT, AND TO TURN R HDG 270 DEGS. ACFT #1 WAS ADVISED OF ACFT #2'S VISUAL SEPARATION AND WAS CLBING FROM 8500 FT TO 17000 FT. WHEN ACFT #2 LEVELED AT 9000 FT, ACFT #1 WAS OBSERVED CLBING FROM 9500 FT. ACFT #1 THEN ADVISED THAT HE WAS FOLLOWING A TCASII RA AND DSNDING FROM 9500 FT. ACFT #1 DSNDED TO 9100 FT OVER ACFT #2 AT 9000 FT. TO PREVENT RECURRENCE: TCASII IS AN EXCELLENT TOOL WHEN UTILIZED APPROPRIATELY. THE CONFLICT COMES WHEN DEFINING 'APPROPRIATE UTILIZATION.' IT APPEARS LOGICAL TO MOST CTLRS THAT WHEN ATC INSTRUCTIONS ARE ISSUED (AS IN THIS SIT) TO PREVENT A COLLISION, PLTS SHOULD FOLLOW ASSIGNED INSTRUCTIONS RATHER THAN TCASII RA'S. I ALSO UNDERSTAND THE DESIGN OF TCASII TO PROVIDE SAFETY WHEN ATC INSTRUCTIONS ARE INADEQUATE. THIS SIT CONFIRMS THE THEORY THAT TCASII RA'S MUST BE A 'SECOND' LINE OF DEFENSE AND SHOULD NOT BE ALLOWED TO TAKE PRECEDENCE OVER ATC INSTRUCTIONS.
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.