B757 crew had less than legal separation in ZHU class a.

Attributes
ACN	454407
Time
Date	199911
Day	Thu
Local Time Of Day	1201 To 1800
Place
State Reference	TX
Altitude	msl bound lower : 28000 msl bound upper : 32000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : vacating altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 20 flight time total : 12000 flight time type : 1800
ASRS Report	454407
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Miss Distance	horizontal : 24000 vertical : 1500
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

While on a vector off das arrival into iah, cleared to descend to FL280. ATC suddenly asked us to tighten our turn to das, then changed to tight turn to 180 degrees, stop descent and climb to FL320. Another flight was given other instructions and they ultimately passed 2000 ft below us. Closest point was 4 NM off right wing and in sight. At the time of incident we thought we were on vector and controller appeared to think we were on direct navigation to das. I never read that clearance back but could have missed it. I don't know. It was my first trip back after 2 months of medical leave and if we did miss a clearance, that could have contributed to it. I did feel behind the aircraft at times during the flight.

Original NASA ASRS Text

Title: B757 CREW HAD LESS THAN LEGAL SEPARATION IN ZHU CLASS A.

Narrative: WHILE ON A VECTOR OFF DAS ARR INTO IAH, CLRED TO DSND TO FL280. ATC SUDDENLY ASKED US TO TIGHTEN OUR TURN TO DAS, THEN CHANGED TO TIGHT TURN TO 180 DEGS, STOP DSCNT AND CLB TO FL320. ANOTHER FLT WAS GIVEN OTHER INSTRUCTIONS AND THEY ULTIMATELY PASSED 2000 FT BELOW US. CLOSEST POINT WAS 4 NM OFF R WING AND IN SIGHT. AT THE TIME OF INCIDENT WE THOUGHT WE WERE ON VECTOR AND CTLR APPEARED TO THINK WE WERE ON DIRECT NAV TO DAS. I NEVER READ THAT CLRNC BACK BUT COULD HAVE MISSED IT. I DON'T KNOW. IT WAS MY FIRST TRIP BACK AFTER 2 MONTHS OF MEDICAL LEAVE AND IF WE DID MISS A CLRNC, THAT COULD HAVE CONTRIBUTED TO IT. I DID FEEL BEHIND THE ACFT AT TIMES DURING THE FLT.

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.