ZSE controller described an on going problem of an aircraft conflicting with itself and activating a...

Narrative:

A C182 called for flight following so I assigned a code. When the data block acquired onto the beacon code it began flashing conflict with what appeared to be the aircraft's previous 1200 code even though they had already switched to the newly assigned code. The altitudes were about 300 to 400 ft apart between the conflict code and the aircraft. I had keyed up to give a traffic alert but then the ghost target went away so I never gave it. This happens randomly and is very disconcerting for the pilots and controllers when you issue a traffic alert for an aircraft at the same location/merged and same altitude. It is impossible to tell the pilot an alternative course of action when the targets are merged! Which way do you tell him to go? This seems to happen about once out of every 15-20 call ups for VFR flight following. We need to find out why this happens and then prevent future occurrences.

Original NASA ASRS Text

Title: ZSE Controller described an on going problem of an aircraft conflicting with itself and activating a 'Conflict Alert' when changed from a VFR code to an IFR code.

Narrative: A C182 called for flight following so I assigned a code. When the data block acquired onto the beacon code it began flashing conflict with what appeared to be the aircraft's previous 1200 code even though they had already switched to the newly assigned code. The altitudes were about 300 to 400 FT apart between the conflict code and the aircraft. I had keyed up to give a traffic alert but then the ghost target went away so I never gave it. This happens randomly and is very disconcerting for the pilots and controllers when you issue a traffic alert for an aircraft at the same location/merged and same altitude. It is impossible to tell the pilot an alternative course of action when the targets are merged! Which way do you tell him to go? This seems to happen about once out of every 15-20 call ups for VFR flight following. We need to find out why this happens and then prevent future occurrences.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1033721
Time
Date	201209
Local Time Of Day	0001-0600
Place
Locale Reference	ZSE.ARTCC
State Reference	WA
Aircraft 1
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Operating Under FAR Part	Part 91
Flight Phase	Climb
Flight Plan	VFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types

ZSE controller described an on going problem of an aircraft conflicting with itself and activating a 'conflict alert' when changed from a VFR code to an IFR code.