Narrative:

After returning to the tower cabin attendant from a break; I was directed to relieve the supervisor from local control south. Traffic was heavy; with 5 aircraft in the south pattern and 10 departures waiting to go. After receiving a position relief briefing from the supervisor; I accepted the position and began to scan the runways and traffic pattern. Approximately 10 seconds after taking the position; I noticed 2 aircraft on final approach; a piper cherokee on short final to runway 7R and a piper seminole about 1.5 mi in trail. Upon further scanning; I noticed that another piper cherokee was out of sequence on a base leg on an intercept course toward the seminole on final. I advised the seminole pilot that it appeared that a student solo cherokee was on base leg and was about to intercept final directly in front of his aircraft. The seminole pilot then advised that he observed the cherokee and was taking evasive maneuvers to avoid an near midair collision. I spoke with the seminole pilot in person; and he advised that his aircraft was within 20 ft ot the cherokee in question. This event was due to 1 of 2 things: 1) supervisor being relieved did not ensure proper sequence for aircraft in pattern. 2) student solo pilot failed to observe traffic and/or follow ATC instructions.

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Original NASA ASRS Text

Title: NMAC OCCURRED BTWN PATTERN TFC WHEN ACFT TURNED BASE CONFLICTING WITH STRAIGHT-IN TFC.

Narrative: AFTER RETURNING TO THE TWR CAB FROM A BREAK; I WAS DIRECTED TO RELIEVE THE SUPVR FROM LCL CTL S. TFC WAS HVY; WITH 5 ACFT IN THE S PATTERN AND 10 DEPS WAITING TO GO. AFTER RECEIVING A POS RELIEF BRIEFING FROM THE SUPVR; I ACCEPTED THE POS AND BEGAN TO SCAN THE RWYS AND TFC PATTERN. APPROX 10 SECONDS AFTER TAKING THE POS; I NOTICED 2 ACFT ON FINAL APCH; A PIPER CHEROKEE ON SHORT FINAL TO RWY 7R AND A PIPER SEMINOLE ABOUT 1.5 MI IN TRAIL. UPON FURTHER SCANNING; I NOTICED THAT ANOTHER PIPER CHEROKEE WAS OUT OF SEQUENCE ON A BASE LEG ON AN INTERCEPT COURSE TOWARD THE SEMINOLE ON FINAL. I ADVISED THE SEMINOLE PLT THAT IT APPEARED THAT A STUDENT SOLO CHEROKEE WAS ON BASE LEG AND WAS ABOUT TO INTERCEPT FINAL DIRECTLY IN FRONT OF HIS ACFT. THE SEMINOLE PLT THEN ADVISED THAT HE OBSERVED THE CHEROKEE AND WAS TAKING EVASIVE MANEUVERS TO AVOID AN NMAC. I SPOKE WITH THE SEMINOLE PLT IN PERSON; AND HE ADVISED THAT HIS ACFT WAS WITHIN 20 FT OT THE CHEROKEE IN QUESTION. THIS EVENT WAS DUE TO 1 OF 2 THINGS: 1) SUPVR BEING RELIEVED DID NOT ENSURE PROPER SEQUENCE FOR ACFT IN PATTERN. 2) STUDENT SOLO PLT FAILED TO OBSERVE TFC AND/OR FOLLOW ATC INSTRUCTIONS.

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.