Narrative:

2 B733 departures approximately 6 mi apart, both climbed to 15000 ft on initial contact. Aircraft #1 was 10 mi south of airport when issued turn to north to join SID. Aircraft #2 was issued turn to east to join his departure (SID) at approximately 5 mi south. His turn was on intercept vector with aircraft #1. At the time issued, aircraft #1 was 4000 ft above aircraft #2, and the climb rates were initially monitored to ensure separation was maintained. I turned my attention to another situation, a VFR conflict. When I resumed my scan, I noticed aircraft #1 had leveled off at 10000 ft and aircraft #2 was climbing through 9000 ft, on intercept heading. Aircraft #2 pilot asked what he should do with the traffic. I told him to maintain visual separation. Aircraft #1 said he had leveled off to configure for something. This action was taken without notification or authority/authorized and caught me completely off guard. In 21 yrs of working radar, I have never had a jet aircraft level for that long (approximately 75 seconds) without any notification or reason on climb out.

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Original NASA ASRS Text

Title: PRECEDING B737 LEVELED OFF FOR SEVERAL SECONDS WITHOUT NOTIFYING MCI DEP, RESULTING IN AN OVERTAKE SITUATION.

Narrative: 2 B733 DEPS APPROX 6 MI APART, BOTH CLBED TO 15000 FT ON INITIAL CONTACT. ACFT #1 WAS 10 MI S OF ARPT WHEN ISSUED TURN TO N TO JOIN SID. ACFT #2 WAS ISSUED TURN TO E TO JOIN HIS DEP (SID) AT APPROX 5 MI S. HIS TURN WAS ON INTERCEPT VECTOR WITH ACFT #1. AT THE TIME ISSUED, ACFT #1 WAS 4000 FT ABOVE ACFT #2, AND THE CLB RATES WERE INITIALLY MONITORED TO ENSURE SEPARATION WAS MAINTAINED. I TURNED MY ATTN TO ANOTHER SIT, A VFR CONFLICT. WHEN I RESUMED MY SCAN, I NOTICED ACFT #1 HAD LEVELED OFF AT 10000 FT AND ACFT #2 WAS CLBING THROUGH 9000 FT, ON INTERCEPT HEADING. ACFT #2 PLT ASKED WHAT HE SHOULD DO WITH THE TFC. I TOLD HIM TO MAINTAIN VISUAL SEPARATION. ACFT #1 SAID HE HAD LEVELED OFF TO CONFIGURE FOR SOMETHING. THIS ACTION WAS TAKEN WITHOUT NOTIFICATION OR AUTH AND CAUGHT ME COMPLETELY OFF GUARD. IN 21 YRS OF WORKING RADAR, I HAVE NEVER HAD A JET ACFT LEVEL FOR THAT LONG (APPROX 75 SECONDS) WITHOUT ANY NOTIFICATION OR REASON ON CLBOUT.

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.