Less than standard separation between air carrier and another IFR aircraft. Operational error.

Attributes
ACN	96184
Time
Date	198810
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mrb
State Reference	WV
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	arrival star : star enroute airway : v3
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 2500
ASRS Report	96184
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 4500 flight time type : 1000
ASRS Report	96183
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	Other
Miss Distance	horizontal : 10000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Cleared by washington center to descend to 11000' and we acknowledged. Passing approximately 12500 the center cleared us again to maintain 11000. While on the arrival route we detected visually another aircraft (Y) ahead at our approximately altitude. Center then advised us we were supposed to be at 12000. We corrected the ATC's 12000' assignment and advised him we were at 11000 per his clearance, and that we had the other aircraft visually. We were then told to maintain a visual on him. No evasive action was necessary or taken. We then noticed the other aircraft being vectored away from us and climbing. Center did not say anything else to us about the mix-up.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN ACR AND ANOTHER IFR ACFT. OPERATIONAL ERROR.

Narrative: CLRED BY WASHINGTON CTR TO DSND TO 11000' AND WE ACKNOWLEDGED. PASSING APPROX 12500 THE CTR CLRED US AGAIN TO MAINTAIN 11000. WHILE ON THE ARR ROUTE WE DETECTED VISUALLY ANOTHER ACFT (Y) AHEAD AT OUR APPROX ALT. CTR THEN ADVISED US WE WERE SUPPOSED TO BE AT 12000. WE CORRECTED THE ATC'S 12000' ASSIGNMENT AND ADVISED HIM WE WERE AT 11000 PER HIS CLRNC, AND THAT WE HAD THE OTHER ACFT VISUALLY. WE WERE THEN TOLD TO MAINTAIN A VISUAL ON HIM. NO EVASIVE ACTION WAS NECESSARY OR TAKEN. WE THEN NOTICED THE OTHER ACFT BEING VECTORED AWAY FROM US AND CLBING. CTR DID NOT SAY ANYTHING ELSE TO US ABOUT THE MIX-UP.

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.