An air carrier medium large transport had an near midair collision with an unknown 'pop up' target.

Attributes
ACN	257345
Time
Date	199311
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sdz airport : rdu
State Reference	NC
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
Flight Phase	cruise other
Route In Use	arrival other arrival star : star enroute airway : zdc
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 9000 flight time type : 6000
ASRS Report	257345
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

I was the first officer during our arrival into rdu. I looked down to tune the VOR and the captain said we had traffic that passed under us left to right (plus or minus 300 ft below us). He reported it to ZDC and center replied a target just popped up at our 6 O'clock position.

Original NASA ASRS Text

Title: AN ACR MLG HAD AN NMAC WITH AN UNKNOWN 'POP UP' TARGET.

Narrative: I WAS THE FO DURING OUR ARR INTO RDU. I LOOKED DOWN TO TUNE THE VOR AND THE CAPT SAID WE HAD TFC THAT PASSED UNDER US L TO R (PLUS OR MINUS 300 FT BELOW US). HE RPTED IT TO ZDC AND CTR REPLIED A TARGET JUST POPPED UP AT OUR 6 O'CLOCK POS.

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.