Atx X descent through occupied altitude had less than standard separation from atx Y. System error.

Attributes
ACN	213103
Time
Date	199206
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : rex
State Reference	FO
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Operator	common carrier : air taxi
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute : direct enroute airway : crp
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air taxi
Make Model Name	Small Transport
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 128 flight time total : 2700 flight time type : 700
ASRS Report	213103
Person 2
Affiliation	company : air taxi
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 flight crewa
Resolutory Action	none taken : unable
Consequence	faa : investigated faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Intra Facility Coordination Failure

Narrative:

Atx Y scheduled nightly cargo flight between monterey, mexico, and harlingen, tx, on victor 10. Almost nightly, atx X passes me. Their departure is 10 mins after me from monterey and they proceed on victor 10 to mcallen, tx. They're in an light transport and so are about 50 KTS faster than my small transport. They are usually passing me at 11000 but want to descend for mcallen. On this evening they were behind me when I was switched from mty center to valley (corpus christi) approach. I listened to harlingen ATIS and communicated with my company prior to establishing contact with valley. On my first contact I heard the controller clear atx X from 11000 to 3000. I called and the controller said I was not radar contact yet. I heard her tell atx X he was not radar contact yet either. I looked out my left side just in time to see atx X immediately above my left wing. I talked to approach on the phone and they said some 'things had fallen into a crease during the handoff from monterey center.' from now on I will switch and communicate immediately on handoffs. Also, I will keep very close track of atx X.

Original NASA ASRS Text

Title: ATX X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ATX Y. SYS ERROR.

Narrative: ATX Y SCHEDULED NIGHTLY CARGO FLT BTWN MONTEREY, MEXICO, AND HARLINGEN, TX, ON VICTOR 10. ALMOST NIGHTLY, ATX X PASSES ME. THEIR DEP IS 10 MINS AFTER ME FROM MONTEREY AND THEY PROCEED ON VICTOR 10 TO MCALLEN, TX. THEY'RE IN AN LTT AND SO ARE ABOUT 50 KTS FASTER THAN MY SMT. THEY ARE USUALLY PASSING ME AT 11000 BUT WANT TO DSND FOR MCALLEN. ON THIS EVENING THEY WERE BEHIND ME WHEN I WAS SWITCHED FROM MTY CTR TO VALLEY (CORPUS CHRISTI) APCH. I LISTENED TO HARLINGEN ATIS AND COMMUNICATED WITH MY COMPANY PRIOR TO ESTABLISHING CONTACT WITH VALLEY. ON MY FIRST CONTACT I HEARD THE CTLR CLR ATX X FROM 11000 TO 3000. I CALLED AND THE CTLR SAID I WAS NOT RADAR CONTACT YET. I HEARD HER TELL ATX X HE WAS NOT RADAR CONTACT YET EITHER. I LOOKED OUT MY L SIDE JUST IN TIME TO SEE ATX X IMMEDIATELY ABOVE MY L WING. I TALKED TO APCH ON THE PHONE AND THEY SAID SOME 'THINGS HAD FALLEN INTO A CREASE DURING THE HDOF FROM MONTEREY CTR.' FROM NOW ON I WILL SWITCH AND COMMUNICATE IMMEDIATELY ON HDOFS. ALSO, I WILL KEEP VERY CLOSE TRACK OF ATX X.

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.