Small aircraft mode C data tag altitude jump. Radar equipment problem ARTS IIIA mode C display.

Attributes
ACN	229134
Time
Date	199212
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tpa
State Reference	FL
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : tpa
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 11
ASRS Report	229134
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : unable
Consequence	faa : investigated
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

I was working the east low position in the tpa TRACON when I observed the mode C readout of small aircraft change from 4000 to 3000 to 4000 to 3100 to 4000 in a matter of 6 seconds for each value described. This is an ongoing problem here at tpa and it will scare you to death at times.

Original NASA ASRS Text

Title: SMA MODE C DATA TAG ALT JUMP. RADAR EQUIP PROBLEM ARTS IIIA MODE C DISPLAY.

Narrative: I WAS WORKING THE E LOW POS IN THE TPA TRACON WHEN I OBSERVED THE MODE C READOUT OF SMA CHANGE FROM 4000 TO 3000 TO 4000 TO 3100 TO 4000 IN A MATTER OF 6 SECONDS FOR EACH VALUE DESCRIBED. THIS IS AN ONGOING PROBLEM HERE AT TPA AND IT WILL SCARE YOU TO DEATH AT TIMES.

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.