False altitude in data block caused controller to issue evasive vectors.

Attributes
ACN	134137
Time
Date	199001
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dfw
State Reference	TX
Altitude	msl bound lower : 7400 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	climbout : intermediate altitude
Route In Use	enroute airway : dfw
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 16
ASRS Report	134137
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

Cga X was inbound over blue ridge VOR, IFR to ftw. Air carrier Y was also inbound over blue ridge VOR, IFR to dfw. Cga X track had been 'coasting' and suddenly indicated an altitude of 9900, about 1 mi behind air carrier X who was at 10,200. The conflict alert went off and I issued a safety advisory and immediate evasive vectors to cga X. The ARTS 303 then resumed correct altitude reporting, showing cga X at 7400, which the pilot verified. The false altitude reporting by our computer caused some trauma to me personally and some agitation to the pilot who was given radical vectors.

Original NASA ASRS Text

Title: FALSE ALT IN DATA BLOCK CAUSED CTLR TO ISSUE EVASIVE VECTORS.

Narrative: CGA X WAS INBND OVER BLUE RIDGE VOR, IFR TO FTW. ACR Y WAS ALSO INBND OVER BLUE RIDGE VOR, IFR TO DFW. CGA X TRACK HAD BEEN 'COASTING' AND SUDDENLY INDICATED AN ALT OF 9900, ABOUT 1 MI BEHIND ACR X WHO WAS AT 10,200. THE CONFLICT ALERT WENT OFF AND I ISSUED A SAFETY ADVISORY AND IMMEDIATE EVASIVE VECTORS TO CGA X. THE ARTS 303 THEN RESUMED CORRECT ALT REPORTING, SHOWING CGA X AT 7400, WHICH THE PLT VERIFIED. THE FALSE ALT REPORTING BY OUR COMPUTER CAUSED SOME TRAUMA TO ME PERSONALLY AND SOME AGITATION TO THE PLT WHO WAS GIVEN RADICAL VECTORS.

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.