Less than standard separation when an air carrier widebody transport is inadvertently descended through the altitude of an opposite direction cpr small transport.

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Attributes
ACN	99575
Time
Date	198812
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : hec
State Reference	CA
Altitude	msl bound lower : 24200 msl bound upper : 24600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 4 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude descent other
Route In Use	enroute airway : j65
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	99575
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : nmac non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : took evasive action none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 400 vertical : 400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

The high altitude sector, responsible for airspace 24000' and above located above my sector showed me an aircraft nwbnd on J65 at FL240. All swbnd lax airport traffic crossing the aircraft (small transport Y) path would be descending to FL250 and my control for descent reference small transport Y. Several aircraft came over to me and I descended them when clear of small transport Y. Widebody transport X came to my frequency and I inadvertently gave the aircraft a descent through small transport Y's altitude. I was busy with other aircraft when I noticed widebody transport X's altitude below FL250 and in conflict with small transport Y. I remembered that I in fact did give widebody transport X a descent clearance. Realizing my mistake I issued a traffic alert to widebody transport X and told him to maintain FL250. He was already through the altitude (FL250), descending, and climbed back to FL250. I found out later that widebody transport X had descended to FL242 and that small transport Y, seeing the widebody transport, took evasive action climbing 600' to FL246. I was relieved from the sector a few mins later.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION WHEN AN ACR WDB IS INADVERTENTLY DESCENDED THROUGH THE ALT OF AN OPPOSITE DIRECTION CPR SMT.

Narrative: THE HIGH ALT SECTOR, RESPONSIBLE FOR AIRSPACE 24000' AND ABOVE LOCATED ABOVE MY SECTOR SHOWED ME AN ACFT NWBND ON J65 AT FL240. ALL SWBND LAX ARPT TFC XING THE ACFT (SMT Y) PATH WOULD BE DESCENDING TO FL250 AND MY CONTROL FOR DSCNT REFERENCE SMT Y. SEVERAL ACFT CAME OVER TO ME AND I DSNDED THEM WHEN CLEAR OF SMT Y. WDB X CAME TO MY FREQUENCY AND I INADVERTENTLY GAVE THE ACFT A DSCNT THROUGH SMT Y'S ALT. I WAS BUSY WITH OTHER ACFT WHEN I NOTICED WDB X'S ALT BELOW FL250 AND IN CONFLICT WITH SMT Y. I REMEMBERED THAT I IN FACT DID GIVE WDB X A DSCNT CLRNC. REALIZING MY MISTAKE I ISSUED A TFC ALERT TO WDB X AND TOLD HIM TO MAINTAIN FL250. HE WAS ALREADY THROUGH THE ALT (FL250), DSNDING, AND CLBED BACK TO FL250. I FOUND OUT LATER THAT WDB X HAD DSNDED TO FL242 AND THAT SMT Y, SEEING THE WDB, TOOK EVASIVE ACTION CLBING 600' TO FL246. I WAS RELIEVED FROM THE SECTOR A FEW MINS LATER.

Data retrieved from NASA's ASRS site as of August 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.