Air carrier X and Y climb descend to same altitude had less than standard separation. System error.

Attributes
ACN	265024
Time
Date	199403
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : phx
State Reference	AZ
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller military : 6 controller radar : 8
ASRS Report	265024
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 21000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was controling 2 acrs (737) with X climbing to FL290. The other Y head-on, descending from FL330 to 12000 ft. They were 35 mi apart when I told the descending aircraft Y to expedite his descent. They still had 15000 ft to go before swapping altitudes. The aircraft were 10 mi apart when I realized I wasn't going to achieve vertical separation. I turned both aircraft 30 degrees right, and tried to stop their altitudes from swapping. This was fruitless, as I gave both aircraft the same altitude FL250. They passed laterally with 3 1/2 mi and same altitude. I believe loss of separation occurred because of my miscalculation of both aircraft's climb and descent rates. That, combined with the rapid closure rate of both acrs. A case of bad judgement.

Original NASA ASRS Text

Title: ACR X AND Y CLB DSND TO SAME ALT HAD LTSS. SYS ERROR.

Narrative: I WAS CTLING 2 ACRS (737) WITH X CLBING TO FL290. THE OTHER Y HEAD-ON, DSNDING FROM FL330 TO 12000 FT. THEY WERE 35 MI APART WHEN I TOLD THE DSNDING ACFT Y TO EXPEDITE HIS DSCNT. THEY STILL HAD 15000 FT TO GO BEFORE SWAPPING ALTS. THE ACFT WERE 10 MI APART WHEN I REALIZED I WASN'T GOING TO ACHIEVE VERT SEPARATION. I TURNED BOTH ACFT 30 DEGS R, AND TRIED TO STOP THEIR ALTS FROM SWAPPING. THIS WAS FRUITLESS, AS I GAVE BOTH ACFT THE SAME ALT FL250. THEY PASSED LATERALLY WITH 3 1/2 MI AND SAME ALT. I BELIEVE LOSS OF SEPARATION OCCURRED BECAUSE OF MY MISCALCULATION OF BOTH ACFT'S CLB AND DSCNT RATES. THAT, COMBINED WITH THE RAPID CLOSURE RATE OF BOTH ACRS. A CASE OF BAD JUDGEMENT.

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.