Narrative:

Anc TRACON radar maintenance advised ATC they were going to perform a maintenance function on the radar. Soon thereafter, things went awry. Aircraft position was instantly off by 10 mi, heading off by 30 degrees. I asked IFR aircraft if he was in VFR conditions, terminated radar service, and advised pilot of radar failure. I instructed pilot to maintain VFR and gave position of known traffic, a potentially conflicting sbound CV58. Pilot advised he had field in sight and was cleared for visual approach. Shortly after, radar returned to normal. No conflict was evident, MD11 shipped to tower. This is the second such occurrence in less than 2 weeks. Supplemental information from acn 348770: radar maintenance advised that they were going to perform maintenance on the rcag. Suddenly all targets were off by several (10-15) mi. The MD80 was nearing terrain in the climb. I could no longer monitor his climb rate with respect to the terrain, and higher MVA he was nearing. Luckily, he was VMC and able to provide his own terrain separation. I had 2 other aircraft (the B737 and a CV58) in the airspace at the time. I felt reasonably certain that they were clear of traffic and terrain, so I took no immediate action. The radar subsequently changed azimuth by about 90 degrees! This same thing happened to me about 2 weeks ago, although this time the technician gave a 'heads up.' but, he said he was only going to work on the rcag, which should not have affected anything. This has got to stop before we kill someone.

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Original NASA ASRS Text

Title: RPTR AT ANC TRACON ALLEGES THAT AIRWAYS FACILITIES TECHNICIAN CAUSED ASR-9 RADAR TO FAIL WHILE HE PERFORMED A MAINT FUNCTION. NO INCIDENTS OCCURRED DURING OUTAGE.

Narrative: ANC TRACON RADAR MAINT ADVISED ATC THEY WERE GOING TO PERFORM A MAINT FUNCTION ON THE RADAR. SOON THEREAFTER, THINGS WENT AWRY. ACFT POS WAS INSTANTLY OFF BY 10 MI, HDG OFF BY 30 DEGS. I ASKED IFR ACFT IF HE WAS IN VFR CONDITIONS, TERMINATED RADAR SVC, AND ADVISED PLT OF RADAR FAILURE. I INSTRUCTED PLT TO MAINTAIN VFR AND GAVE POS OF KNOWN TFC, A POTENTIALLY CONFLICTING SBOUND CV58. PLT ADVISED HE HAD FIELD IN SIGHT AND WAS CLRED FOR VISUAL APCH. SHORTLY AFTER, RADAR RETURNED TO NORMAL. NO CONFLICT WAS EVIDENT, MD11 SHIPPED TO TWR. THIS IS THE SECOND SUCH OCCURRENCE IN LESS THAN 2 WKS. SUPPLEMENTAL INFO FROM ACN 348770: RADAR MAINT ADVISED THAT THEY WERE GOING TO PERFORM MAINT ON THE RCAG. SUDDENLY ALL TARGETS WERE OFF BY SEVERAL (10-15) MI. THE MD80 WAS NEARING TERRAIN IN THE CLB. I COULD NO LONGER MONITOR HIS CLB RATE WITH RESPECT TO THE TERRAIN, AND HIGHER MVA HE WAS NEARING. LUCKILY, HE WAS VMC AND ABLE TO PROVIDE HIS OWN TERRAIN SEPARATION. I HAD 2 OTHER ACFT (THE B737 AND A CV58) IN THE AIRSPACE AT THE TIME. I FELT REASONABLY CERTAIN THAT THEY WERE CLR OF TFC AND TERRAIN, SO I TOOK NO IMMEDIATE ACTION. THE RADAR SUBSEQUENTLY CHANGED AZIMUTH BY ABOUT 90 DEGS! THIS SAME THING HAPPENED TO ME ABOUT 2 WKS AGO, ALTHOUGH THIS TIME THE TECHNICIAN GAVE A 'HEADS UP.' BUT, HE SAID HE WAS ONLY GOING TO WORK ON THE RCAG, WHICH SHOULD NOT HAVE AFFECTED ANYTHING. THIS HAS GOT TO STOP BEFORE WE KILL SOMEONE.

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.