Less than standard separation between 2 air carrier aircraft. Opal error.

Attributes
ACN	181776
Time
Date	199106
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : hou
State Reference	TX
Altitude	msl bound lower : 6000 msl bound upper : 6300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iah
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	181776
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
ASRS Report	181775
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation other anomaly other other anomaly other
Independent Detector	other other : unspecified atc
Resolutory Action	controller : issued new clearance none taken : unable other
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Intra Facility Coordination Failure Operational Error

Narrative:

I was working arrival east with air carrier X instructed to depart badgr heading 300 vectors ILS 12R. When he was about 15 mi northeast of hou I issued traffic on air carrier Y at approximately 8 mi. My air carrier X was descending to 6000 ft. When the other mode C indicated 5100 ft I thought the aircraft would level at 5000 ft as is normal in this area. 100 ft being within mode C tolerance and commonly seen. Next sweep I saw 5400 ft and became alarmed. I pointed this out to the departure controller who did not appear to understand. I then issued a 90 degree turn to my air carrier X to avoid the other aircraft. Separation was lost when the other aircraft leveled at 6000 ft. Supplemental information from acn 181775: I was working departure north radar trying to get 15 mi intrail separation on 2 aircraft. I also climbed air carrier Y off hobby. I was quick looking the arrival controller. The tmc then told me to level my air carrier Y at 6000 ft MSL as he pointed out an arrival not on the arrival east position identifier. I leveled air carrier Y and turned him to avoid getting too close to the arrival.

Original NASA ASRS Text

Title: LTSS BTWN 2 ACR ACFT. OPAL ERROR.

Narrative: I WAS WORKING ARR E WITH ACR X INSTRUCTED TO DEPART BADGR HDG 300 VECTORS ILS 12R. WHEN HE WAS ABOUT 15 MI NE OF HOU I ISSUED TFC ON ACR Y AT APPROX 8 MI. MY ACR X WAS DSNDING TO 6000 FT. WHEN THE OTHER MODE C INDICATED 5100 FT I THOUGHT THE ACFT WOULD LEVEL AT 5000 FT AS IS NORMAL IN THIS AREA. 100 FT BEING WITHIN MODE C TOLERANCE AND COMMONLY SEEN. NEXT SWEEP I SAW 5400 FT AND BECAME ALARMED. I POINTED THIS OUT TO THE DEP CTLR WHO DID NOT APPEAR TO UNDERSTAND. I THEN ISSUED A 90 DEG TURN TO MY ACR X TO AVOID THE OTHER ACFT. SEPARATION WAS LOST WHEN THE OTHER ACFT LEVELED AT 6000 FT. SUPPLEMENTAL INFO FROM ACN 181775: I WAS WORKING DEP N RADAR TRYING TO GET 15 MI INTRAIL SEPARATION ON 2 ACFT. I ALSO CLBED ACR Y OFF HOBBY. I WAS QUICK LOOKING THE ARR CTLR. THE TMC THEN TOLD ME TO LEVEL MY ACR Y AT 6000 FT MSL AS HE POINTED OUT AN ARR NOT ON THE ARR E POS IDENTIFIER. I LEVELED ACR Y AND TURNED HIM TO AVOID GETTING TOO CLOSE TO THE ARR.

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.