Narrative:

Flight instructor with a japanese student (1.0 hours solo). I was to evaluate my student's ability to enter and exit high density traffic patterns (non-radar). My aircraft was right downwind abeam the approach end of runway 21. Another aircraft reported a 2 mile right base. The tower controller instructed us to follow that traffic which required us to make a 45 degree correction to the left. The student responded that he was looking for the traffic. I spotted the traffic and instructed my student to look further to his left for the traffic. I then heard another aircraft report 7.2 DME on the localizer (runway 21). The controller then told us to widen out even more to follow the traffic on base (not yet in sight to my student) and told the other aircraft to report 4.2 DME. My student reported traffic in sight (on base). We were cleared to land behind that traffic. We were on a wide right base about a mi from the localizer when the controller asked the position of the aircraft on final. They responded 4.4 DME. We were then instructed to follow this traffic. I informed the tower that the traffic was not in sight. I could tell by his voice that he was uncomfortable with what was happening when he issued a second TA about the traffic about 4.3 DME. I again replied 'negative contact.' he immediately issued instructions to 'turn left now!!' I took the controls and made a 60 degree bank climbing turn at approach speed. After I rolled out of the turn I saw the aircraft on the localizer directly ahead but slightly lower. We passed within 100 ft of each other. Had we been at the same altitude there would have been no time to avoid a head on midair collision. The remainder of the flight was uneventful. The next day I contacted the controller I spoke with on the radio. We both understand each other's position and each explained our side of the story, and we resolved the situation.

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Original NASA ASRS Text

Title: INSTRUCTOR WITH A STUDENT ON BASE LEG TAKES EVASIVE ACTION CLB TURN TO AVOID TFC NOT OBSERVED BUT SOUNDING CLOSE BY TWR CTLR RESULTS IN NMAC.

Narrative: FLT INSTRUCTOR WITH A JAPANESE STUDENT (1.0 HRS SOLO). I WAS TO EVALUATE MY STUDENT'S ABILITY TO ENTER AND EXIT HIGH DENSITY TFC PATTERNS (NON-RADAR). MY ACFT WAS R DOWNWIND ABEAM THE APCH END OF RWY 21. ANOTHER ACFT RPTED A 2 MILE R BASE. THE TWR CTLR INSTRUCTED US TO FOLLOW THAT TFC WHICH REQUIRED US TO MAKE A 45 DEG CORRECTION TO THE L. THE STUDENT RESPONDED THAT HE WAS LOOKING FOR THE TFC. I SPOTTED THE TFC AND INSTRUCTED MY STUDENT TO LOOK FURTHER TO HIS L FOR THE TFC. I THEN HEARD ANOTHER ACFT RPT 7.2 DME ON THE LOC (RWY 21). THE CTLR THEN TOLD US TO WIDEN OUT EVEN MORE TO FOLLOW THE TFC ON BASE (NOT YET IN SIGHT TO MY STUDENT) AND TOLD THE OTHER ACFT TO RPT 4.2 DME. MY STUDENT RPTED TFC IN SIGHT (ON BASE). WE WERE CLRED TO LAND BEHIND THAT TFC. WE WERE ON A WIDE R BASE ABOUT A MI FROM THE LOC WHEN THE CTLR ASKED THE POS OF THE ACFT ON FINAL. THEY RESPONDED 4.4 DME. WE WERE THEN INSTRUCTED TO FOLLOW THIS TFC. I INFORMED THE TWR THAT THE TFC WAS NOT IN SIGHT. I COULD TELL BY HIS VOICE THAT HE WAS UNCOMFORTABLE WITH WHAT WAS HAPPENING WHEN HE ISSUED A SECOND TA ABOUT THE TFC ABOUT 4.3 DME. I AGAIN REPLIED 'NEGATIVE CONTACT.' HE IMMEDIATELY ISSUED INSTRUCTIONS TO 'TURN L NOW!!' I TOOK THE CTLS AND MADE A 60 DEG BANK CLBING TURN AT APCH SPD. AFTER I ROLLED OUT OF THE TURN I SAW THE ACFT ON THE LOC DIRECTLY AHEAD BUT SLIGHTLY LOWER. WE PASSED WITHIN 100 FT OF EACH OTHER. HAD WE BEEN AT THE SAME ALT THERE WOULD HAVE BEEN NO TIME TO AVOID A HEAD ON MIDAIR COLLISION. THE REMAINDER OF THE FLT WAS UNEVENTFUL. THE NEXT DAY I CONTACTED THE CTLR I SPOKE WITH ON THE RADIO. WE BOTH UNDERSTAND EACH OTHER'S POS AND EACH EXPLAINED OUR SIDE OF THE STORY, AND WE RESOLVED THE SITUATION.

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.