Light transport mode C data tag altitude jump. Radar equipment problem ARTS III a mode C display.

Attributes
ACN	228799
Time
Date	199212
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tpa
State Reference	FL
Altitude	msl bound lower : 5000 msl bound upper : 5000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : tpa
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	228799
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
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:

Light transport at 50 inbound to srq. I was working srq approach sector (n-scope, digital radar). Mode C readout varied from 4900 ft to 2900 ft from sweep to sweep for at least 10 mi then to 6800 ft and back to 3000 ft. Was reported to supervisor but luckily there was no conflicting traffic and I was not busy or this would have been a serious situation. Pilot report no previous problems with transponder.

Original NASA ASRS Text

Title: LTT MODE C DATA TAG ALT JUMP. RADAR EQUIP PROBLEM ARTS III A MODE C DISPLAY.

Narrative: LTT AT 50 INBOUND TO SRQ. I WAS WORKING SRQ APCH SECTOR (N-SCOPE, DIGITAL RADAR). MODE C READOUT VARIED FROM 4900 FT TO 2900 FT FROM SWEEP TO SWEEP FOR AT LEAST 10 MI THEN TO 6800 FT AND BACK TO 3000 FT. WAS RPTED TO SUPVR BUT LUCKILY THERE WAS NO CONFLICTING TFC AND I WAS NOT BUSY OR THIS WOULD HAVE BEEN A SERIOUS SITUATION. PLT RPT NO PREVIOUS PROBLEMS WITH TRANSPONDER.

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.