Narrative:

My student and I had returned to the apa airport at the end of a training flight and at the time of the incident had performed 2 touch-and-goes on apa runway 17L. After the second takeoff, we informed the tower controller that the next landing would be a full stop. On left downwind approximately abeam the tower (1, in diagram), we were instructed to continue our downwind to accommodate other landing traffic I believe stated to be over cherry creek reservoir and that tower would call our base turn. Still on downwind and approximately over arapaho road (2), about 1 mi north of the runway 17L threshold 'latitude' I saw traffic lower at my 9-10 O'clock position on final (3) and I reported this traffic using all of that location information. I do not remember the tower's response, but I remember being confident that that was our traffic to follow and after allowing maybe 5 seconds to pass, I instructed my student to turn base (4) and begin our descent. A few seconds later the tower questioned what I was doing and instructed something like 'keep the left turn coming.' I interpreted this to mean that I was to continue the left turn base to final and proceed down final. Shortly thereafter, my student and I saw another aircraft above and to the west on a right base turning final above us (5). Somehow this was apparently the traffic we were to have followed. Upon a quick query of the tower as to what they wanted me to do to resolve the conflict, they told me to 'keep the left turn coming' or something to that effect. I asked if they wanted me to continue the turn to the east and they said 'yes.' in fact, after a further interchange, I completed a left 360 degree turn and was cleared to land on runway 17L. There was definitely some miscom here. First of all, I did not follow tower's command that they would call my base turn, but after reporting the traffic on final as I did, I was under the impression that that was our traffic to follow. I am not sure why tower didn't say something about continuing my downwind further to the north after my report. The command to 'keep the left turn coming' was not very clear. A command of 'do a left 360 degree turn' or 'continue the left turn to an easterly heading' would have been much clrer. What will I do differently in the future? I am in the habit of and I teach identing traffic pointouts by reporting traffic direction from me ('traffic 10 O'clock...'), relative altitude ('...lower...') and direction if appropriate ('...on final.'), not just 'traffic in sight.' in the future I will preface this with 'traffic to follow in sight, 10 O'clock position, lower, etc.' this way, ATC will know that it is my understanding that I am to follow that aircraft. What should apa tower have done differently? The use of more standard phraseology would have helped. And I still don't know if the traffic that I interacted with was idented earlier by tower as being my traffic to follow or if they miscalled my traffic to follow earlier. Only a playback of the tapes would solve that mystery.

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Original NASA ASRS Text

Title: A C172 TRAINING FLT HAS AN NMAC WITH ANOTHER GA ACFT IN THE TFC PATTERN AT APA, CO.

Narrative: MY STUDENT AND I HAD RETURNED TO THE APA ARPT AT THE END OF A TRAINING FLT AND AT THE TIME OF THE INCIDENT HAD PERFORMED 2 TOUCH-AND-GOES ON APA RWY 17L. AFTER THE SECOND TKOF, WE INFORMED THE TWR CTLR THAT THE NEXT LNDG WOULD BE A FULL STOP. ON L DOWNWIND APPROX ABEAM THE TWR (1, IN DIAGRAM), WE WERE INSTRUCTED TO CONTINUE OUR DOWNWIND TO ACCOMMODATE OTHER LNDG TFC I BELIEVE STATED TO BE OVER CHERRY CREEK RESERVOIR AND THAT TWR WOULD CALL OUR BASE TURN. STILL ON DOWNWIND AND APPROX OVER ARAPAHO ROAD (2), ABOUT 1 MI N OF THE RWY 17L THRESHOLD 'LATITUDE' I SAW TFC LOWER AT MY 9-10 O'CLOCK POS ON FINAL (3) AND I RPTED THIS TFC USING ALL OF THAT LOCATION INFO. I DO NOT REMEMBER THE TWR'S RESPONSE, BUT I REMEMBER BEING CONFIDENT THAT THAT WAS OUR TFC TO FOLLOW AND AFTER ALLOWING MAYBE 5 SECONDS TO PASS, I INSTRUCTED MY STUDENT TO TURN BASE (4) AND BEGIN OUR DSCNT. A FEW SECONDS LATER THE TWR QUESTIONED WHAT I WAS DOING AND INSTRUCTED SOMETHING LIKE 'KEEP THE L TURN COMING.' I INTERPED THIS TO MEAN THAT I WAS TO CONTINUE THE L TURN BASE TO FINAL AND PROCEED DOWN FINAL. SHORTLY THEREAFTER, MY STUDENT AND I SAW ANOTHER ACFT ABOVE AND TO THE W ON A R BASE TURNING FINAL ABOVE US (5). SOMEHOW THIS WAS APPARENTLY THE TFC WE WERE TO HAVE FOLLOWED. UPON A QUICK QUERY OF THE TWR AS TO WHAT THEY WANTED ME TO DO TO RESOLVE THE CONFLICT, THEY TOLD ME TO 'KEEP THE L TURN COMING' OR SOMETHING TO THAT EFFECT. I ASKED IF THEY WANTED ME TO CONTINUE THE TURN TO THE E AND THEY SAID 'YES.' IN FACT, AFTER A FURTHER INTERCHANGE, I COMPLETED A L 360 DEG TURN AND WAS CLRED TO LAND ON RWY 17L. THERE WAS DEFINITELY SOME MISCOM HERE. FIRST OF ALL, I DID NOT FOLLOW TWR'S COMMAND THAT THEY WOULD CALL MY BASE TURN, BUT AFTER RPTING THE TFC ON FINAL AS I DID, I WAS UNDER THE IMPRESSION THAT THAT WAS OUR TFC TO FOLLOW. I AM NOT SURE WHY TWR DIDN'T SAY SOMETHING ABOUT CONTINUING MY DOWNWIND FURTHER TO THE N AFTER MY RPT. THE COMMAND TO 'KEEP THE L TURN COMING' WAS NOT VERY CLR. A COMMAND OF 'DO A L 360 DEG TURN' OR 'CONTINUE THE L TURN TO AN EASTERLY HDG' WOULD HAVE BEEN MUCH CLRER. WHAT WILL I DO DIFFERENTLY IN THE FUTURE? I AM IN THE HABIT OF AND I TEACH IDENTING TFC POINTOUTS BY RPTING TFC DIRECTION FROM ME ('TFC 10 O'CLOCK...'), RELATIVE ALT ('...LOWER...') AND DIRECTION IF APPROPRIATE ('...ON FINAL.'), NOT JUST 'TFC IN SIGHT.' IN THE FUTURE I WILL PREFACE THIS WITH 'TFC TO FOLLOW IN SIGHT, 10 O'CLOCK POS, LOWER, ETC.' THIS WAY, ATC WILL KNOW THAT IT IS MY UNDERSTANDING THAT I AM TO FOLLOW THAT ACFT. WHAT SHOULD APA TWR HAVE DONE DIFFERENTLY? THE USE OF MORE STANDARD PHRASEOLOGY WOULD HAVE HELPED. AND I STILL DON'T KNOW IF THE TFC THAT I INTERACTED WITH WAS IDENTED EARLIER BY TWR AS BEING MY TFC TO FOLLOW OR IF THEY MISCALLED MY TFC TO FOLLOW EARLIER. ONLY A PLAYBACK OF THE TAPES WOULD SOLVE THAT MYSTERY.

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.