A handoff was made to approach control on a B737 inbound to clt maintaining 11000 ft. Another B737 was on a converging course descending, but still on center frequency. The TRACON controller thought that the second B737 was descending to 12000 ft and would pass over his aircraft, however, the second B737 continued descent through 12000 ft. The TRACON controller issued a descent to the first B737 to avoid the other aircraft.

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Attributes
ACN	383820
Time
Date	199710
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : clt
State Reference	NC
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl tracon : clt artcc : zhu
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	383820
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 500 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I had aircraft #1 on my frequency established on shine arrival, but still in center airspace at 11000 ft. Aircraft #2 was being worked by center descending out of 13600 ft, 10 mi west of aircraft #1, on a heading to intercept the shine arrival. Because I felt the 2 aircraft were going to merge, I issued merging traffic procedures to aircraft #1 stating 'company would level off 1000 ft above aircraft #1.' due to aircraft #2 rate of descent, I issued a descent clearance to aircraft #1, while aircraft #1 was still in center's airspace. Aircraft #2 passed directly over aircraft #1 level at 11000 ft. I truly believe if I had not descended aircraft #1 in center's airspace, a midair would have resulted.

Original NASA ASRS Text

Title: A HDOF WAS MADE TO APCH CTL ON A B737 INBOUND TO CLT MAINTAINING 11000 FT. ANOTHER B737 WAS ON A CONVERGING COURSE DSNDING, BUT STILL ON CTR FREQ. THE TRACON CTLR THOUGHT THAT THE SECOND B737 WAS DSNDING TO 12000 FT AND WOULD PASS OVER HIS ACFT, HOWEVER, THE SECOND B737 CONTINUED DSCNT THROUGH 12000 FT. THE TRACON CTLR ISSUED A DSCNT TO THE FIRST B737 TO AVOID THE OTHER ACFT.

Narrative: I HAD ACFT #1 ON MY FREQ ESTABLISHED ON SHINE ARR, BUT STILL IN CTR AIRSPACE AT 11000 FT. ACFT #2 WAS BEING WORKED BY CTR DSNDING OUT OF 13600 FT, 10 MI W OF ACFT #1, ON A HDG TO INTERCEPT THE SHINE ARR. BECAUSE I FELT THE 2 ACFT WERE GOING TO MERGE, I ISSUED MERGING TFC PROCS TO ACFT #1 STATING 'COMPANY WOULD LEVEL OFF 1000 FT ABOVE ACFT #1.' DUE TO ACFT #2 RATE OF DSCNT, I ISSUED A DSCNT CLRNC TO ACFT #1, WHILE ACFT #1 WAS STILL IN CTR'S AIRSPACE. ACFT #2 PASSED DIRECTLY OVER ACFT #1 LEVEL AT 11000 FT. I TRULY BELIEVE IF I HAD NOT DSNDED ACFT #1 IN CTR'S AIRSPACE, A MIDAIR WOULD HAVE RESULTED.

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.