Narrative:

As we were returning to twf from the southwest after a training flight; another cherokee reported several mi north. The local controller instructed my student to report on a left downwind for runway 25. The other cherokee was instructed to report 2 mi north. My student reported left downwind and initiated the landing sequence. As we turned base I looked for the other cherokee; but did not see it. I wasn't worried because I had not heard him report 2 mi out; so I assumed that he was still more than 2 mi from the airport. The cherokee then reported 2 mi out and he was told that he was '#2 behind a cherokee turning from downwind to left base.' he acknowledged. As my student starting making his turn from base to final the controller told the other cherokee 'you are ahead of the other cherokee; you are cleared to land; aircraft X you are now #2.' I told the tower that we did not have the other plane in sight. My student was now in his turn to final and I saw the other plane to our right -- further from the airport; and slightly below us. I took control of the plane; initiated a left climbing turn to avoid a collision. The controller then instructed us to continue our turn and follow the other cherokee. When things calmed down the controller explained that he had misjudged our distance because of our crab angle and thought we were further out than we were. Had we not started the climbing turn when we did the other plane would have been within a very few feet of us when we completed the turn; or possibly have collided with us. I believe there were 2 factors in this near miss. The other cherokee seems to have been much closer than 2 mi when he reported. The local controller grossly misjudged our distance from the field.

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Original NASA ASRS Text

Title: PA28 ON BASE TO TWF RWY 25 EXPERIENCED CONFLICT WITH STRAIGHT IN TFC; ATC'S SPACING/SEQUENCING JUDGEMENT LISTED AS CONTRIBUTORY.

Narrative: AS WE WERE RETURNING TO TWF FROM THE SW AFTER A TRAINING FLT; ANOTHER CHEROKEE RPTED SEVERAL MI N. THE LCL CTLR INSTRUCTED MY STUDENT TO RPT ON A L DOWNWIND FOR RWY 25. THE OTHER CHEROKEE WAS INSTRUCTED TO RPT 2 MI N. MY STUDENT RPTED L DOWNWIND AND INITIATED THE LNDG SEQUENCE. AS WE TURNED BASE I LOOKED FOR THE OTHER CHEROKEE; BUT DID NOT SEE IT. I WASN'T WORRIED BECAUSE I HAD NOT HEARD HIM RPT 2 MI OUT; SO I ASSUMED THAT HE WAS STILL MORE THAN 2 MI FROM THE ARPT. THE CHEROKEE THEN RPTED 2 MI OUT AND HE WAS TOLD THAT HE WAS '#2 BEHIND A CHEROKEE TURNING FROM DOWNWIND TO L BASE.' HE ACKNOWLEDGED. AS MY STUDENT STARTING MAKING HIS TURN FROM BASE TO FINAL THE CTLR TOLD THE OTHER CHEROKEE 'YOU ARE AHEAD OF THE OTHER CHEROKEE; YOU ARE CLRED TO LAND; ACFT X YOU ARE NOW #2.' I TOLD THE TWR THAT WE DID NOT HAVE THE OTHER PLANE IN SIGHT. MY STUDENT WAS NOW IN HIS TURN TO FINAL AND I SAW THE OTHER PLANE TO OUR R -- FURTHER FROM THE ARPT; AND SLIGHTLY BELOW US. I TOOK CTL OF THE PLANE; INITIATED A L CLBING TURN TO AVOID A COLLISION. THE CTLR THEN INSTRUCTED US TO CONTINUE OUR TURN AND FOLLOW THE OTHER CHEROKEE. WHEN THINGS CALMED DOWN THE CTLR EXPLAINED THAT HE HAD MISJUDGED OUR DISTANCE BECAUSE OF OUR CRAB ANGLE AND THOUGHT WE WERE FURTHER OUT THAN WE WERE. HAD WE NOT STARTED THE CLBING TURN WHEN WE DID THE OTHER PLANE WOULD HAVE BEEN WITHIN A VERY FEW FEET OF US WHEN WE COMPLETED THE TURN; OR POSSIBLY HAVE COLLIDED WITH US. I BELIEVE THERE WERE 2 FACTORS IN THIS NEAR MISS. THE OTHER CHEROKEE SEEMS TO HAVE BEEN MUCH CLOSER THAN 2 MI WHEN HE RPTED. THE LCL CTLR GROSSLY MISJUDGED OUR DISTANCE FROM THE FIELD.

Data retrieved from NASA's ASRS site as of January 2009 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.