Controller claims that mode C jumping or erroneous altitude indicated is causing problems.

Attributes
ACN	225364
Time
Date	199211
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : tpa
State Reference	FL
Altitude	msl bound lower : 13000 msl bound upper : 13000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : tpa
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	climbout : initial
Route In Use	departure other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : approach
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 5 controller radar : 10
ASRS Report	225364
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 24000 vertical : 800
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

Was observing erroneous mode C readout of an additional aircraft departing tpa and was distracted from the normal flow of traffic. The 2 aircraft should not have been in the same area and minor evasive action delaying the arrival was accomplished in time to resolve any conflict. The 'jumping' of mode C altitudes is becoming a continual problem and is beginning to erode the confidence of the beacon system. Tpa form 6190-2, 'ARTS problem report' was completed and given to the area manager. Callback conversation with reporter revealed the following information: reporter claims that this is still an ongoing problem. They have 2 radar sites with 1 of them digitized. The erroneous mode C generally happens with every third aircraft. Most controllers have become used to working with this problem, so there has not been any reported incidents. The erroneous altitude usually lasts from 30 seconds to 1 min. Facility is tracking the problem, but it has been ongoing for about 3 yrs. Ucr was filed 4 weeks ago. Reporter states the facility management is good to work with, but they apparently do not think that this is a safety issue. Track dropping was another problem for awhile, however, airway facilities discovered that a new building is being constructed nearby was causing the problem and are in the process of rectifying it now. Reporter also stated that 2 facility 'ARTS problem report' forms have been submitted on this.

Original NASA ASRS Text

Title: CTLR CLAIMS THAT MODE C JUMPING OR ERRONEOUS ALT INDICATED IS CAUSING PROBLEMS.

Narrative: WAS OBSERVING ERRONEOUS MODE C READOUT OF AN ADDITIONAL ACFT DEPARTING TPA AND WAS DISTRACTED FROM THE NORMAL FLOW OF TFC. THE 2 ACFT SHOULD NOT HAVE BEEN IN THE SAME AREA AND MINOR EVASIVE ACTION DELAYING THE ARR WAS ACCOMPLISHED IN TIME TO RESOLVE ANY CONFLICT. THE 'JUMPING' OF MODE C ALTS IS BECOMING A CONTINUAL PROBLEM AND IS BEGINNING TO ERODE THE CONFIDENCE OF THE BEACON SYS. TPA FORM 6190-2, 'ARTS PROBLEM RPT' WAS COMPLETED AND GIVEN TO THE AREA MGR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CLAIMS THAT THIS IS STILL AN ONGOING PROBLEM. THEY HAVE 2 RADAR SITES WITH 1 OF THEM DIGITIZED. THE ERRONEOUS MODE C GENERALLY HAPPENS WITH EVERY THIRD ACFT. MOST CTLRS HAVE BECOME USED TO WORKING WITH THIS PROBLEM, SO THERE HAS NOT BEEN ANY RPTED INCIDENTS. THE ERRONEOUS ALT USUALLY LASTS FROM 30 SECONDS TO 1 MIN. FACILITY IS TRACKING THE PROBLEM, BUT IT HAS BEEN ONGOING FOR ABOUT 3 YRS. UCR WAS FILED 4 WKS AGO. RPTR STATES THE FACILITY MGMNT IS GOOD TO WORK WITH, BUT THEY APPARENTLY DO NOT THINK THAT THIS IS A SAFETY ISSUE. TRACK DROPPING WAS ANOTHER PROBLEM FOR AWHILE, HOWEVER, AIRWAY FACILITIES DISCOVERED THAT A NEW BUILDING IS BEING CONSTRUCTED NEARBY WAS CAUSING THE PROBLEM AND ARE IN THE PROCESS OF RECTIFYING IT NOW. RPTR ALSO STATED THAT 2 FACILITY 'ARTS PROBLEM RPT' FORMS HAVE BEEN SUBMITTED ON THIS.

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.