Air carrier descended below assigned altitude resulting in less than standard separation with a cga.

Attributes
ACN	116257
Time
Date	198907
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fim
State Reference	CA
Altitude	msl bound lower : 17200 msl bound upper : 18000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller military : 2 controller radar : 5
ASRS Report	117257
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 250 flight time total : 17000 flight time type : 250
ASRS Report	116237
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 200
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Air carrier X was proceeding to lax and cga Y into sna. Cga Y was at 17000' and air carrier X was stopped at FL180 while the cga Y went under him, and was told to expect clearance for the profile at fim. I called the traffic to both aircraft and told air carrier X to expect lower when clear. Air carrier X went through FL180 descending to 15000' as he later said. Sep was lost and was recorded on our operational error detection machine. There was no time to correct the error due to descent rate of air carrier X. Supplemental information from acn 116237: as I looked back at the instrument panel I noticed that we were descending to 17000' and that the altitude alerter had been reset to 15000'.

Original NASA ASRS Text

Title: ACR DESCENDED BELOW ASSIGNED ALT RESULTING IN LESS THAN STANDARD SEPARATION WITH A CGA.

Narrative: ACR X WAS PROCEEDING TO LAX AND CGA Y INTO SNA. CGA Y WAS AT 17000' AND ACR X WAS STOPPED AT FL180 WHILE THE CGA Y WENT UNDER HIM, AND WAS TOLD TO EXPECT CLRNC FOR THE PROFILE AT FIM. I CALLED THE TFC TO BOTH ACFT AND TOLD ACR X TO EXPECT LOWER WHEN CLR. ACR X WENT THROUGH FL180 DSNDING TO 15000' AS HE LATER SAID. SEP WAS LOST AND WAS RECORDED ON OUR OPERROR DETECTION MACHINE. THERE WAS NO TIME TO CORRECT THE ERROR DUE TO DSCNT RATE OF ACR X. SUPPLEMENTAL INFO FROM ACN 116237: AS I LOOKED BACK AT THE INSTRUMENT PANEL I NOTICED THAT WE WERE DSNDING TO 17000' AND THAT THE ALT ALERTER HAD BEEN RESET TO 15000'.

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.