Narrative:

Aircraft X departed ZZZ on an IFR flight plan southwest bound. He checked on; was radar identified leaving 1;500 ft and climbed to 8;000 ft. I spoke to another aircraft; then returned to the C172 and turned him right heading 250. I had 2 other aircraft in the vicinity of the C172 that could be a factor so I just so happened to be paying close attention. The aircraft was last seen at 1;700 ft; but then I noticed the altitude showed XXX; which would typically mean a climb or descent too fast for our old equipment to keep up with. The aircraft's tag then showed CST and wasn't staying with the primary target. This also happens occasionally on our old equipment when an aircraft is moving too slow or fast for the ARTS iie to track. When the tag re-acquired; the aircraft appeared to be tracking northbound. I asked the pilot to confirm heading 250. The pilot initially started to respond normally; then shouted 'wait a minute; wait a minute;' pause; 'we have a problem.' I issued the altimeter and gave the pilot his indicated altitude of 1;100 ft. I tried to point out the airport; but the ceiling was 600 ft ovc. Shortly after the pilot stated he could see the ground. I asked the pilot if he was climbing or needed to return to the airport to land. He said he needed to land and needed a heading. We declared it an emergency and I vectored the aircraft below the MVA to safety. I told the pilot to fly heading 360. Shortly after; I noticed the aircraft appeared to be tracking westbound. I asked the pilot about it and he corrected. I instructed him to stay below the clouds and issued small vectors at a time to keep the pilot from becoming any more disoriented. I continued to point out the airport hoping the pilot would see the runway. He kept the ground in sight and my supervisor instructed me to clear the aircraft for a contact approach. I cleared him for a contact approach to either runway and the pilot got the airport in sight about a mile north of the runway. The tower gave me permission to clear the aircraft to land as we did not want the pilot to worry about changing frequencies. The pilot advised me when he had landed safely and I switched him to tower frequency. In the end we found out that his artificial horizon indicator wasn't functioning correctly. Recommendation; though everything turned out ok; the result could have been devastating. We listened to and watched the replay today and it was apparent that the pilot was within seconds of losing his life. We also spoke to the pilot and he thought everything seemed normal. When I asked him to confirm his heading; he realized something was wrong. He was in a downward spiral to the ground and banking to the right to pull out of it. The pilot got as low as 800 ft MSL; or about 200 ft AGL. In the replay; which is more advanced than our actual radar equipment; the pilot's incorrect track and altitude would have been noticed instantly. The replay on nop showed the pilot spiraling and descending where all I could see on my radar was some XXX's for altitude; and CST on a coasting tag. Loss of radar identification and these tracking problems happen on our old radar equipment so often that it isn't initially as alarming as it should be. Those few seconds wasted not knowing the true track and altitude could have cost this pilot his life had I not used gut instinct. This event really alarmed me and knew others must be notified of our equipment issues. It makes it very hard to work with equipment that you can't trust! Does someone have to lose their life in order for someone to listen and realize that it imperative for us to have new equipment to work our increasing volume of traffic safely?

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Original NASA ASRS Text

Title: TRACON Controller described an ATC declared emergency event when noting an IFR C172 data tag displaying 'XXX' and CST. The pilot then indicated that there was a problem and the needed to land.

Narrative: Aircraft X departed ZZZ on an IFR flight plan southwest bound. He checked on; was RADAR identified leaving 1;500 FT and climbed to 8;000 FT. I spoke to another aircraft; then returned to the C172 and turned him right heading 250. I had 2 other aircraft in the vicinity of the C172 that could be a factor so I just so happened to be paying close attention. The aircraft was last seen at 1;700 FT; but then I noticed the altitude showed XXX; which would typically mean a climb or descent too fast for our old equipment to keep up with. The aircraft's tag then showed CST and wasn't staying with the primary target. This also happens occasionally on our old equipment when an aircraft is moving too slow or fast for the ARTS IIE to track. When the tag re-acquired; the aircraft appeared to be tracking northbound. I asked the pilot to confirm heading 250. The pilot initially started to respond normally; then shouted 'Wait a minute; wait a minute;' pause; 'We have a problem.' I issued the altimeter and gave the pilot his indicated altitude of 1;100 FT. I tried to point out the airport; but the ceiling was 600 FT OVC. Shortly after the pilot stated he could see the ground. I asked the pilot if he was climbing or needed to return to the airport to land. He said he needed to land and needed a heading. We declared it an emergency and I vectored the aircraft below the MVA to safety. I told the pilot to fly heading 360. Shortly after; I noticed the aircraft appeared to be tracking westbound. I asked the pilot about it and he corrected. I instructed him to stay below the clouds and issued small vectors at a time to keep the pilot from becoming any more disoriented. I continued to point out the airport hoping the pilot would see the runway. He kept the ground in sight and my Supervisor instructed me to clear the aircraft for a Contact Approach. I cleared him for a Contact Approach to either runway and the pilot got the airport in sight about a mile north of the runway. The Tower gave me permission to clear the aircraft to land as we did not want the pilot to worry about changing frequencies. The pilot advised me when he had landed safely and I switched him to Tower frequency. In the end we found out that his artificial horizon indicator wasn't functioning correctly. Recommendation; though everything turned out OK; the result could have been devastating. We listened to and watched the replay today and it was apparent that the pilot was within seconds of losing his life. We also spoke to the pilot and he thought everything seemed normal. When I asked him to confirm his heading; he realized something was wrong. He was in a downward spiral to the ground and banking to the right to pull out of it. The pilot got as low as 800 FT MSL; or about 200 FT AGL. In the replay; which is more advanced than our actual RADAR equipment; the pilot's incorrect track and altitude would have been noticed instantly. The replay on NOP showed the pilot spiraling and descending where all I could see on my RADAR was some XXX's for altitude; and CST on a coasting tag. Loss of RADAR identification and these tracking problems happen on our old RADAR equipment so often that it isn't initially as alarming as it should be. Those few seconds wasted not knowing the true track and altitude could have cost this pilot his life had I not used gut instinct. This event really alarmed me and knew others must be notified of our equipment issues. It makes it very hard to work with equipment that you can't trust! Does someone have to lose their life in order for someone to listen and realize that it imperative for us to have new equipment to work our increasing volume of traffic safely?

Data retrieved from NASA's ASRS site as of July 2013 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.