Mode C data tag altitude jump. Radar equipment problems ARTS IIIA mode C display.

Attributes
ACN	229126
Time
Date	199212
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : tpa
State Reference	FL
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : tpa
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 23
ASRS Report	229126
Person 2
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

Narrative:

While working the combined positions of sarasota north, sarasota south, macdill sectors I observed 7 aircraft both VFR and IFR with assigned beacon codes, mode C altitudes deviation more than 500 ft gain and loss of altitude. This is a normal occurrence with tpa's antiquated beacon system and has been increasing since the advent of TCASII equipped aircraft and the TCA mode C requirements by local aircraft.

Original NASA ASRS Text

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

Narrative: WHILE WORKING THE COMBINED POSITIONS OF SARASOTA N, SARASOTA S, MACDILL SECTORS I OBSERVED 7 ACFT BOTH VFR AND IFR WITH ASSIGNED BEACON CODES, MODE C ALTS DEV MORE THAN 500 FT GAIN AND LOSS OF ALT. THIS IS A NORMAL OCCURRENCE WITH TPA'S ANTIQUATED BEACON SYS AND HAS BEEN INCREASING SINCE THE ADVENT OF TCASII EQUIPPED ACFT AND THE TCA MODE C REQUIREMENTS BY LCL ACFT.

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.