Air carrier X had less than standard separation from air carrier Y. System error.

Attributes
ACN	185659
Time
Date	199108
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 1500 msl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : atl tower : rsw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	185659
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X was on ILS approach to runway 26R and was in trail of air carrier Y. Air carrier X closed to within 2 1/2 mi of air carrier Y and the local controller asked air carrier X if he had the traffic ahead in sight. Air carrier X said affirmative and was then told to maintain visual separation from the traffic. Air carrier X then said he had seen the traffic only 3 seconds before he reported it in sight and asked what the spacing was. The local controller told air carrier X 2 mi and 1000 ft. Air carrier X was then side-stepped to runway 26L and cleared to land on 26L. The side-step action was not required but it did insure air carrier X would be able to land. After landing the captain on air carrier X called and questioned the separation between his aircraft and air carrier Y. I believe that if the visibility had been better and air carrier X had seen the traffic sooner he would have been less concerned about the spacing. I also believe that the aircraft knew 2 mi was less than required and that was another reason he called the facility.

Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR X WAS ON ILS APCH TO RWY 26R AND WAS IN TRAIL OF ACR Y. ACR X CLOSED TO WITHIN 2 1/2 MI OF ACR Y AND THE LCL CTLR ASKED ACR X IF HE HAD THE TFC AHEAD IN SIGHT. ACR X SAID AFFIRMATIVE AND WAS THEN TOLD TO MAINTAIN VISUAL SEPARATION FROM THE TFC. ACR X THEN SAID HE HAD SEEN THE TFC ONLY 3 SECONDS BEFORE HE RPTED IT IN SIGHT AND ASKED WHAT THE SPACING WAS. THE LCL CTLR TOLD ACR X 2 MI AND 1000 FT. ACR X WAS THEN SIDE-STEPPED TO RWY 26L AND CLRED TO LAND ON 26L. THE SIDE-STEP ACTION WAS NOT REQUIRED BUT IT DID INSURE ACR X WOULD BE ABLE TO LAND. AFTER LNDG THE CAPT ON ACR X CALLED AND QUESTIONED THE SEPARATION BTWN HIS ACFT AND ACR Y. I BELIEVE THAT IF THE VISIBILITY HAD BEEN BETTER AND ACR X HAD SEEN THE TFC SOONER HE WOULD HAVE BEEN LESS CONCERNED ABOUT THE SPACING. I ALSO BELIEVE THAT THE ACFT KNEW 2 MI WAS LESS THAN REQUIRED AND THAT WAS ANOTHER REASON HE CALLED THE FACILITY.

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.