Narrative:

I was working the south radar position at portland, me, TRACON. Traffic was mdt-heavy with the majority of the traffic between ene VOR and the pwm airport. Small aircraft X 25-35 mi northwest of the airport swbnd was being given advisories at 6500'. Almost all my attention was on the aircraft in the vicinity of the airport and I did not notice when I lost radar on the 6500' traffic. When I did get a chance to review all my traffic I observed a target squawking 1200 at 6500' swbnd in just about the same area where small aircraft X was flying. Assuming that small aircraft X had changed his beacon code to 1200 west/O notifying me because he couldn't get through on the frequency (this happens several times a week), and because it was a VFR aircraft and I was still very busy I did not question the new beacon code. Finally, the aircraft asked if I was going to hand him off did I discover that I had lost radar on small aircraft X there was a VFR aircraft at the same altitude in the same vicinity. This also happened to be in an area near (but not in) a section of airspace where we have a problem with radar coverage due to a well documented radar problem at pwm. (Someone built a hotel next to the radar site). I advised small aircraft X that radar contact was lost and subsequently reidented him 1 mi from aircraft Y on a converging course. I issued traffic, which small aircraft X saw immediately. I see two problems in what occurred. I made the 'big' mistake by assuming that small aircraft X changed to a 1200 code. The radar problems at pwm are definitely more of a problem than the FAA flight check first revealed. In this instance, I lost radar on an aircraft at 6500' where we have a minimum vectoring altitude of 4000'. At the same time I had radar on aircraft Y within a couple of mi of small aircraft X, same altitude. Assuming if I had one of the airplanes, I would surely have both, I believed I only had one airplane there. The two aircraft got within 1 mi of each other at the same altitude and could have gotten closer. The FAA should take another look at portland's radar.

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Original NASA ASRS Text

Title: APCH CTLR WAS ATTEMPTING TO PROVIDE RADAR SERVICE IN AN AREA THAT IS A KNOWN AREA OF NON-RADAR COVERAGE. SITUATION; RADAR ANTENNA OBSTRUCTION.

Narrative: I WAS WORKING THE S RADAR POS AT PORTLAND, ME, TRACON. TFC WAS MDT-HVY WITH THE MAJORITY OF THE TFC BTWN ENE VOR AND THE PWM ARPT. SMA X 25-35 MI NW OF THE ARPT SWBND WAS BEING GIVEN ADVISORIES AT 6500'. ALMOST ALL MY ATTN WAS ON THE ACFT IN THE VICINITY OF THE ARPT AND I DID NOT NOTICE WHEN I LOST RADAR ON THE 6500' TFC. WHEN I DID GET A CHANCE TO REVIEW ALL MY TFC I OBSERVED A TARGET SQUAWKING 1200 AT 6500' SWBND IN JUST ABOUT THE SAME AREA WHERE SMA X WAS FLYING. ASSUMING THAT SMA X HAD CHANGED HIS BEACON CODE TO 1200 W/O NOTIFYING ME BECAUSE HE COULDN'T GET THROUGH ON THE FREQ (THIS HAPPENS SEVERAL TIMES A WK), AND BECAUSE IT WAS A VFR ACFT AND I WAS STILL VERY BUSY I DID NOT QUESTION THE NEW BEACON CODE. FINALLY, THE ACFT ASKED IF I WAS GOING TO HAND HIM OFF DID I DISCOVER THAT I HAD LOST RADAR ON SMA X THERE WAS A VFR ACFT AT THE SAME ALT IN THE SAME VICINITY. THIS ALSO HAPPENED TO BE IN AN AREA NEAR (BUT NOT IN) A SECTION OF AIRSPACE WHERE WE HAVE A PROB WITH RADAR COVERAGE DUE TO A WELL DOCUMENTED RADAR PROB AT PWM. (SOMEONE BUILT A HOTEL NEXT TO THE RADAR SITE). I ADVISED SMA X THAT RADAR CONTACT WAS LOST AND SUBSEQUENTLY REIDENTED HIM 1 MI FROM ACFT Y ON A CONVERGING COURSE. I ISSUED TFC, WHICH SMA X SAW IMMEDIATELY. I SEE TWO PROBS IN WHAT OCCURRED. I MADE THE 'BIG' MISTAKE BY ASSUMING THAT SMA X CHANGED TO A 1200 CODE. THE RADAR PROBS AT PWM ARE DEFINITELY MORE OF A PROB THAN THE FAA FLT CHK FIRST REVEALED. IN THIS INSTANCE, I LOST RADAR ON AN ACFT AT 6500' WHERE WE HAVE A MINIMUM VECTORING ALT OF 4000'. AT THE SAME TIME I HAD RADAR ON ACFT Y WITHIN A COUPLE OF MI OF SMA X, SAME ALT. ASSUMING IF I HAD ONE OF THE AIRPLANES, I WOULD SURELY HAVE BOTH, I BELIEVED I ONLY HAD ONE AIRPLANE THERE. THE TWO ACFT GOT WITHIN 1 MI OF EACH OTHER AT THE SAME ALT AND COULD HAVE GOTTEN CLOSER. THE FAA SHOULD TAKE ANOTHER LOOK AT PORTLAND'S RADAR.

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.