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ZSE controller experienced loss of separation with two in-trail aircraft at FL350 with closely matched speeds.
| Attributes | |
| ACN | 627973 |
| Time | |
| Date | 200408 |
| Day | Wed |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : mlp.vor |
| State Reference | ID |
| Altitude | msl single value : 35000 |
| Environment | |
| Weather Elements | Thunderstorm |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zse.artcc tower : pdt.tower |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : zse.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Experience | controller military : 4 controller radar : 22 |
| ASRS Report | 627973 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Events | |
| Anomaly | conflict : airborne less severe non adherence : required legal separation |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance flight crew : took evasive action |
| Consequence | faa : investigated |
| Supplementary | |
| Problem Areas | ATC Human Performance |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error |
Narrative:
I received air carrier X and air carrier Y from ZLC and was informed that air carrier X was speed restr by 10 KTS to stay behind air carrier Y. The ground speeds were consistent with the leading aircraft about 448 KTS and the trailing aircraft at 432 KTS. When the data blocks started flashing I observed the ground speeds at 446 KTS and the trailer at 438 KTS. The immediate alert went off and I had turned the trailing aircraft 20 degrees right and the leading aircraft 10 degrees to the left. I was restr in turning the aircraft to the left because of the thunderstorm just south of mlp VOR. I was relieved from the position and an investigation into loss of separation was started. I think that some things to look for in future events would be to match the speeds or assign speeds to both aircraft and that if aircraft are deviating that they are assigned headings so as not to allow the aircraft to come together.
Original NASA ASRS Text
Title: ZSE CTLR EXPERIENCED LOSS OF SEPARATION WITH TWO IN-TRAIL ACFT AT FL350 WITH CLOSELY MATCHED SPDS.
Narrative: I RECEIVED ACR X AND ACR Y FROM ZLC AND WAS INFORMED THAT ACR X WAS SPD RESTR BY 10 KTS TO STAY BEHIND ACR Y. THE GND SPDS WERE CONSISTENT WITH THE LEADING ACFT ABOUT 448 KTS AND THE TRAILING ACFT AT 432 KTS. WHEN THE DATA BLOCKS STARTED FLASHING I OBSERVED THE GND SPDS AT 446 KTS AND THE TRAILER AT 438 KTS. THE IMMEDIATE ALERT WENT OFF AND I HAD TURNED THE TRAILING ACFT 20 DEGS R AND THE LEADING ACFT 10 DEGS TO THE L. I WAS RESTR IN TURNING THE ACFT TO THE L BECAUSE OF THE TSTM JUST S OF MLP VOR. I WAS RELIEVED FROM THE POS AND AN INVESTIGATION INTO LOSS OF SEPARATION WAS STARTED. I THINK THAT SOME THINGS TO LOOK FOR IN FUTURE EVENTS WOULD BE TO MATCH THE SPDS OR ASSIGN SPDS TO BOTH ACFT AND THAT IF ACFT ARE DEVIATING THAT THEY ARE ASSIGNED HDGS SO AS NOT TO ALLOW THE ACFT TO COME TOGETHER.
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.