Air carrier deviating around WX causes loss of separation with another aircraft.

Attributes
ACN	125148
Time
Date	198910
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cha
State Reference	TN
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	125148
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 24000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X departed atl at XA57Z J89 msp. At XB10Z air carrier X requested deviation west of course for WX. Since there was no WX depicted on the radar, and previous aircraft on J89 in the same area had not deviated, a minor deviation was expected. Air carrier Y departed atl at XA52Z, atl cha bna stl, and was 10 mi west of air carrier X when air carrier X requested deviation. At XB12Z, it became evident that air carrier X had made a more abrupt turn than was expected and now his flight was converging with air carrier Y. Air carrier X made a 45 degree left turn and the conflict alert did not activate until separation was lost. Air carrier X's altitude was amended to establish vertical separation, but the clearance was not timely enough to prevent an operational error. Our radar does not give a clear indication of where WX is located, therefore we are unable to provide assistance around the WX. We have to just situation and wait to see which way the aircraft will go and when all the traffic you are working is deviating, it reduces your workable space in which you have to control traffic. If we had a clear depiction of the WX, then we would have better control of the traffic because it would eliminate the waiting and guessing.

Original NASA ASRS Text

Title: ACR DEVIATING AROUND WX CAUSES LOSS OF SEPARATION WITH ANOTHER ACFT.

Narrative: ACR X DEPARTED ATL AT XA57Z J89 MSP. AT XB10Z ACR X REQUESTED DEVIATION W OF COURSE FOR WX. SINCE THERE WAS NO WX DEPICTED ON THE RADAR, AND PREVIOUS ACFT ON J89 IN THE SAME AREA HAD NOT DEVIATED, A MINOR DEVIATION WAS EXPECTED. ACR Y DEPARTED ATL AT XA52Z, ATL CHA BNA STL, AND WAS 10 MI W OF ACR X WHEN ACR X REQUESTED DEVIATION. AT XB12Z, IT BECAME EVIDENT THAT ACR X HAD MADE A MORE ABRUPT TURN THAN WAS EXPECTED AND NOW HIS FLT WAS CONVERGING WITH ACR Y. ACR X MADE A 45 DEG LEFT TURN AND THE CONFLICT ALERT DID NOT ACTIVATE UNTIL SEPARATION WAS LOST. ACR X'S ALT WAS AMENDED TO ESTABLISH VERTICAL SEPARATION, BUT THE CLRNC WAS NOT TIMELY ENOUGH TO PREVENT AN OPERATIONAL ERROR. OUR RADAR DOES NOT GIVE A CLEAR INDICATION OF WHERE WX IS LOCATED, THEREFORE WE ARE UNABLE TO PROVIDE ASSISTANCE AROUND THE WX. WE HAVE TO JUST SIT AND WAIT TO SEE WHICH WAY THE ACFT WILL GO AND WHEN ALL THE TFC YOU ARE WORKING IS DEVIATING, IT REDUCES YOUR WORKABLE SPACE IN WHICH YOU HAVE TO CTL TFC. IF WE HAD A CLEAR DEPICTION OF THE WX, THEN WE WOULD HAVE BETTER CTL OF THE TFC BECAUSE IT WOULD ELIMINATE THE WAITING AND GUESSING.

Data retrieved from NASA's ASRS site as of August 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.