Narrative:

I was returning to land at cos from a CFI training flight. I was flying from the right seat and my instructor was in the left seat. As we approached cos, approach control told us to 'expect left base for runway 17L.' we were then handed off to cos tower on 119.90. Upon reporting in to cos tower, we were told by a controller to enter left base for runway 17L, then were told to change that to runway 12 and that we were cleared to land #2 following a cessna on 1/2 mi final for runway 17R. We reported back cleared to land #2 behind the cessna on short final and that we had the landing traffic in sight. We were 2 mi out and I was completing my prelndg checks. As I was turning base to final (sun was a factor), I was looking down to reconfirm we had 3 green lights on the landing gear indicators. At that moment, my instructor yelled 'whoa' and she immediately pushed forward on the yoke. I looked up and saw the cessna heading toward us at a range of 1/2 mi and between 100-200 ft above. I, myself, pushed forward on the yoke. After the cessna passed, another controller came on the frequency and said 'sorry about that cherokee XXX, you are cleared to land on runway 12.' we repeated clearance back to him. He repeated it back to us. I once again repeated it back. We landed without incident. I don't think the other cessna ever saw us. I believe he was on a downwind for runway 17R. He was instructed to land behind us. If he was in the downwind for runway 17R, the tower should have had him do a 360 degree turn for spacing.

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Original NASA ASRS Text

Title: PA28 INSTRUCTOR ALERTS STUDENT OF DEVELOPING CONFLICT AS COS LCL CTLR NEGLECTS TO ISSUE OTHER CONFLICTING CESSNA TFC ON BASE LEG TO ANOTHER RWY.

Narrative: I WAS RETURNING TO LAND AT COS FROM A CFI TRAINING FLT. I WAS FLYING FROM THE R SEAT AND MY INSTRUCTOR WAS IN THE L SEAT. AS WE APCHED COS, APCH CTL TOLD US TO 'EXPECT L BASE FOR RWY 17L.' WE WERE THEN HANDED OFF TO COS TWR ON 119.90. UPON RPTING IN TO COS TWR, WE WERE TOLD BY A CTLR TO ENTER L BASE FOR RWY 17L, THEN WERE TOLD TO CHANGE THAT TO RWY 12 AND THAT WE WERE CLRED TO LAND #2 FOLLOWING A CESSNA ON 1/2 MI FINAL FOR RWY 17R. WE RPTED BACK CLRED TO LAND #2 BEHIND THE CESSNA ON SHORT FINAL AND THAT WE HAD THE LNDG TFC IN SIGHT. WE WERE 2 MI OUT AND I WAS COMPLETING MY PRELNDG CHKS. AS I WAS TURNING BASE TO FINAL (SUN WAS A FACTOR), I WAS LOOKING DOWN TO RECONFIRM WE HAD 3 GREEN LIGHTS ON THE LNDG GEAR INDICATORS. AT THAT MOMENT, MY INSTRUCTOR YELLED 'WHOA' AND SHE IMMEDIATELY PUSHED FORWARD ON THE YOKE. I LOOKED UP AND SAW THE CESSNA HEADING TOWARD US AT A RANGE OF 1/2 MI AND BTWN 100-200 FT ABOVE. I, MYSELF, PUSHED FORWARD ON THE YOKE. AFTER THE CESSNA PASSED, ANOTHER CTLR CAME ON THE FREQ AND SAID 'SORRY ABOUT THAT CHEROKEE XXX, YOU ARE CLRED TO LAND ON RWY 12.' WE REPEATED CLRNC BACK TO HIM. HE REPEATED IT BACK TO US. I ONCE AGAIN REPEATED IT BACK. WE LANDED WITHOUT INCIDENT. I DON'T THINK THE OTHER CESSNA EVER SAW US. I BELIEVE HE WAS ON A DOWNWIND FOR RWY 17R. HE WAS INSTRUCTED TO LAND BEHIND US. IF HE WAS IN THE DOWNWIND FOR RWY 17R, THE TWR SHOULD HAVE HAD HIM DO A 360 DEG TURN FOR SPACING.

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.