Air carrier Y descended to air carrier X altitude with less than standard separation. System error.

Attributes
ACN	114868
Time
Date	198906
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zoa
State Reference	CA
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : on vectors enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	114868
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Miss Distance	horizontal : 27000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

2 parallel aircraft: air carrier X at 24000', air carrier Y at 25000'. Descended air carrier Y from 25000 to 24000' with less then 5 mi latitude sep.

Original NASA ASRS Text

Title: ACR Y DESCENDED TO ACR X ALT WITH LESS THAN STANDARD SEPARATION. SYSTEM ERROR.

Narrative: 2 PARALLEL ACFT: ACR X AT 24000', ACR Y AT 25000'. DSNDED ACR Y FROM 25000 TO 24000' WITH LESS THEN 5 MI LAT SEP.

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.