Narrative:

By LOA between dfw TRACON and ZFW; aircraft on the same radial of the SID shall be assigned speeds when less than 8 mi in trail. Aircraft #1 was an east satellite airport departure going to ohio. Aircraft #2 was from another satellite airport going to little rock; ar. Dfw departure control requested that aircraft #1 and #2 be given different departure radials of the dal 7. This would result in approach control not having to sequence the aircraft and assign speeds on the same radial. I requested that the aircraft be left on the radial that made up the little rock transition and put in trail with speed. Aircraft #1 checked on frequency climbing to 17000 ft and I cleared the aircraft to FL230. Aircraft #2 checked on frequency climbing to 17000 ft with a speed restr of 250 KTS. Aircraft #2 was higher than aircraft #1; but aircraft #1 had already been cleared to FL230. Aircraft #2 was overtaking aircraft #1. (Aircraft should have had speeds assigned per the LOA; but I do not know if aircraft #1 had a speed assigned.) I instructed aircraft #1 to increase rate of climb through FL190 to obtain vertical separation from aircraft #2. Based on performance characteristics of the aircraft; I believed vertical separation could be obtained before longitudinal separation was lost. The aircraft had less than 5 mi separation before 1000 ft vertical separation was obtained. The situation occurred; I believe; because of the differences in perception between approach control and en route center control. To the approach; controller's world ends 30 mi from the airport at 17000 ft. The center controller sees an aircraft going to ohio and another going to little rock and is looking 150-250 mi into the future. The approach controller sees a 95 degree turn for 30 mi and the 7 mi in trail as his 2 options. The center controller sees one aircraft going 1000 ft and another going 200 mi and sees vertical as the best option. 7 mi of separation is twice what the approach controller needs for separation. 7 mi with an overtake on 2 aircraft going the same altitude is a critical situation to an en route controller needing a 5 mi minimum. 2 worlds -- 2 perspectives -- this is the reason for LOA's.

Google
 

Original NASA ASRS Text

Title: ZFW CTLR EXPRESSED FRUSTRATION WITH POTENTIAL TFC CONFLICT RECEIVED FROM 10 AND PERCEPTION DIFFERENCES BTWN ARTCC AND APCH CTLRS.

Narrative: BY LOA BTWN DFW TRACON AND ZFW; ACFT ON THE SAME RADIAL OF THE SID SHALL BE ASSIGNED SPDS WHEN LESS THAN 8 MI IN TRAIL. ACFT #1 WAS AN E SATELLITE ARPT DEP GOING TO OHIO. ACFT #2 WAS FROM ANOTHER SATELLITE ARPT GOING TO LITTLE ROCK; AR. DFW DEP CTL REQUESTED THAT ACFT #1 AND #2 BE GIVEN DIFFERENT DEP RADIALS OF THE DAL 7. THIS WOULD RESULT IN APCH CTL NOT HAVING TO SEQUENCE THE ACFT AND ASSIGN SPDS ON THE SAME RADIAL. I REQUESTED THAT THE ACFT BE LEFT ON THE RADIAL THAT MADE UP THE LITTLE ROCK TRANSITION AND PUT IN TRAIL WITH SPD. ACFT #1 CHKED ON FREQ CLBING TO 17000 FT AND I CLRED THE ACFT TO FL230. ACFT #2 CHKED ON FREQ CLBING TO 17000 FT WITH A SPD RESTR OF 250 KTS. ACFT #2 WAS HIGHER THAN ACFT #1; BUT ACFT #1 HAD ALREADY BEEN CLRED TO FL230. ACFT #2 WAS OVERTAKING ACFT #1. (ACFT SHOULD HAVE HAD SPDS ASSIGNED PER THE LOA; BUT I DO NOT KNOW IF ACFT #1 HAD A SPD ASSIGNED.) I INSTRUCTED ACFT #1 TO INCREASE RATE OF CLB THROUGH FL190 TO OBTAIN VERT SEPARATION FROM ACFT #2. BASED ON PERFORMANCE CHARACTERISTICS OF THE ACFT; I BELIEVED VERT SEPARATION COULD BE OBTAINED BEFORE LONGITUDINAL SEPARATION WAS LOST. THE ACFT HAD LESS THAN 5 MI SEPARATION BEFORE 1000 FT VERT SEPARATION WAS OBTAINED. THE SIT OCCURRED; I BELIEVE; BECAUSE OF THE DIFFERENCES IN PERCEPTION BTWN APCH CTL AND ENRTE CTR CTL. TO THE APCH; CTLR'S WORLD ENDS 30 MI FROM THE ARPT AT 17000 FT. THE CTR CTLR SEES AN ACFT GOING TO OHIO AND ANOTHER GOING TO LITTLE ROCK AND IS LOOKING 150-250 MI INTO THE FUTURE. THE APCH CTLR SEES A 95 DEG TURN FOR 30 MI AND THE 7 MI IN TRAIL AS HIS 2 OPTIONS. THE CTR CTLR SEES ONE ACFT GOING 1000 FT AND ANOTHER GOING 200 MI AND SEES VERT AS THE BEST OPTION. 7 MI OF SEPARATION IS TWICE WHAT THE APCH CTLR NEEDS FOR SEPARATION. 7 MI WITH AN OVERTAKE ON 2 ACFT GOING THE SAME ALT IS A CRITICAL SIT TO AN ENRTE CTLR NEEDING A 5 MI MINIMUM. 2 WORLDS -- 2 PERSPECTIVES -- THIS IS THE REASON FOR LOA'S.

Data retrieved from NASA's ASRS site as of January 2009 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.