Narrative:

While giving training at the casino low sector, I observed air carrier X, assigned altitude 11000 appear to be climbing from assigned altitude. At the time, ngx Y was directly overhead at 12000. My trainee asked air carrier X to verify altitude as 11000. The pilots response was 'negative, TCASII alert' and was climbing. My trainee cleared air carrier X to descend and maintain 11000. I intervened at this time and had air carrier X continue climb because air carrier X was at 12200. The problem arose because the primary radar was down for maintenance, which occurs every wed. The other reason was air carrier X followed his TCASII advisory because of VFR traffic at 10500, and climbed through ngx Y at 12000. The 2 targets merged. Only the good lord knows how close they were. Because of the radar outage, we were losing beacons at 12000 and below. Also, the beacon displays were giving erroneous altitude readouts and false tracking. This happened at an extremely busy time in one of the most complex and busy sectors we have due to the mixture of slow aircraft and jets. This is also augmented by the numerous VFR aircraft flying along the shoreline. Air carrier X, when questioned about the altitude advised us he tried to contact us but the transmission was blocked due to frequency congestion. Callback conversation with reporter revealed the following information: reporter claims that the radar is taken by airway facilities personnel every wed for 2 to 4 hours for routine maintenance, unless WX conditions or traffic conditions will not permit. However, many times, traffic situations occur where primary radar site coverage is needed, but not available. When they switch to another radar site, they have difficulty seeing aircraft below 10000 ft. Supposedly, many targets go into coast status or they lose data blocks. The radar site involved is 'trevose.' reporter thinks that this scheduled maintenance should be done when there is little traffic, not during the day or evening shifts on wkdays. Ucr not field. Qtp representative aware of problem and so is facility management, but this has been going on for a long time with nobody doing anything about it.

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Original NASA ASRS Text

Title: ACR ACFT RESPONDING TO TCASII RA CLBS THROUGH AN OCCUPIED ALT. PRIMARY RADAR WAS OUT FOR ROUTINE WKLY MAINT.

Narrative: WHILE GIVING TRAINING AT THE CASINO LOW SECTOR, I OBSERVED ACR X, ASSIGNED ALT 11000 APPEAR TO BE CLBING FROM ASSIGNED ALT. AT THE TIME, NGX Y WAS DIRECTLY OVERHEAD AT 12000. MY TRAINEE ASKED ACR X TO VERIFY ALT AS 11000. THE PLTS RESPONSE WAS 'NEGATIVE, TCASII ALERT' AND WAS CLBING. MY TRAINEE CLRED ACR X TO DSND AND MAINTAIN 11000. I INTERVENED AT THIS TIME AND HAD ACR X CONTINUE CLB BECAUSE ACR X WAS AT 12200. THE PROBLEM AROSE BECAUSE THE PRIMARY RADAR WAS DOWN FOR MAINT, WHICH OCCURS EVERY WED. THE OTHER REASON WAS ACR X FOLLOWED HIS TCASII ADVISORY BECAUSE OF VFR TFC AT 10500, AND CLBED THROUGH NGX Y AT 12000. THE 2 TARGETS MERGED. ONLY THE GOOD LORD KNOWS HOW CLOSE THEY WERE. BECAUSE OF THE RADAR OUTAGE, WE WERE LOSING BEACONS AT 12000 AND BELOW. ALSO, THE BEACON DISPLAYS WERE GIVING ERRONEOUS ALT READOUTS AND FALSE TRACKING. THIS HAPPENED AT AN EXTREMELY BUSY TIME IN ONE OF THE MOST COMPLEX AND BUSY SECTORS WE HAVE DUE TO THE MIXTURE OF SLOW ACFT AND JETS. THIS IS ALSO AUGMENTED BY THE NUMEROUS VFR ACFT FLYING ALONG THE SHORELINE. ACR X, WHEN QUESTIONED ABOUT THE ALT ADVISED US HE TRIED TO CONTACT US BUT THE XMISSION WAS BLOCKED DUE TO FREQ CONGESTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CLAIMS THAT THE RADAR IS TAKEN BY AIRWAY FACILITIES PERSONNEL EVERY WED FOR 2 TO 4 HRS FOR ROUTINE MAINT, UNLESS WX CONDITIONS OR TFC CONDITIONS WILL NOT PERMIT. HOWEVER, MANY TIMES, TFC SITUATIONS OCCUR WHERE PRIMARY RADAR SITE COVERAGE IS NEEDED, BUT NOT AVAILABLE. WHEN THEY SWITCH TO ANOTHER RADAR SITE, THEY HAVE DIFFICULTY SEEING ACFT BELOW 10000 FT. SUPPOSEDLY, MANY TARGETS GO INTO COAST STATUS OR THEY LOSE DATA BLOCKS. THE RADAR SITE INVOLVED IS 'TREVOSE.' RPTR THINKS THAT THIS SCHEDULED MAINT SHOULD BE DONE WHEN THERE IS LITTLE TFC, NOT DURING THE DAY OR EVENING SHIFTS ON WKDAYS. UCR NOT FIELD. QTP REPRESENTATIVE AWARE OF PROBLEM AND SO IS FACILITY MGMNT, BUT THIS HAS BEEN GOING ON FOR A LONG TIME WITH NOBODY DOING ANYTHING ABOUT IT.

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.