Narrative:

A helicopter was VFR inbound from the north/northeast; approved to land at the ramp. Aircraft X a VFR inbound from the southeast cleared to land runway 31. Aircraft Z; IFR; visual approach from the south; cleared to land runway 35R. Aircraft Y; IFR; visual approach; cleared to land runway 35R. Aircraft X was on approach to runway 31 while aircraft Z was on final approach to runway 35R. Because of the disparities in speed; aircraft X was estimated to reach the eastern edge of runway 35R at the same time aircraft Z was estimated to cross the runway threshold. Approximately 1/2-3/4 mile from the eastern edge of runway 35R; I instructed aircraft X to; 'go around; turn right heading 350'. Aircraft X read back the instructions correctly and complied. Aircraft Z landed without incident. Aircraft X was turned right to a 350 heading because the helicopter was crossing the departure end of runway 35R; on track to cross over the departure end of runway 31; en-route to the ramp. I provided aircraft X with traffic information on the helicopter which he reported in sight. Aircraft X was instructed to; 'pass behind the helicopter; turn left and enter a left downwind for runway 35L; runway 35L cleared to land'. Additionally; I reiterated the same instructions two additional times which were read back correctly. I observed aircraft X turn left and commit to a westerly heading as instructed. Aircraft Y was approximately two miles from runway 35R threshold.I turned around to face south and visually verify that aircraft Z had exited runway 35R and was taxiing as instructed; observe the progress of aircraft Y; and then turned to the west to observe the progress of the helicopter. As I was searching the left downwind to runway 35L for aircraft X and aircraft Y was coming to a stop near taxiway E5; aircraft X contacted the ATCT stating; 'tower; there is an aircraft landing opposite direction to us'. I turned around and looked at the approach end of runway 17L and aircraft X had landed and was rolling out between taxiways E3/E4. Aircraft Y contacted the ATCT and said; 'we're stopped on the runway at E5'. I informed aircraft X that he landed runway 17L and taxied him to parking. Once aircraft X was off the runway; I taxied aircraft Y to parking and then read aircraft X the 'brasher notification'.reevaluate traffic priorities and be cognizant of which aircraft require greater portions of available attention.

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Original NASA ASRS Text

Title: COS Tower Controller reported a small general aviation aircraft landed on the wrong runway opposite direction of an air carrier that had also landed and was on the runway.

Narrative: A helicopter was VFR inbound from the N/NE; approved to land at the ramp. Aircraft X a VFR inbound from the southeast cleared to land Runway 31. Aircraft Z; IFR; Visual Approach from the south; cleared to land Runway 35R. Aircraft Y; IFR; Visual Approach; cleared to land Runway 35R. Aircraft X was on approach to Runway 31 while Aircraft Z was on final approach to Runway 35R. Because of the disparities in speed; Aircraft X was estimated to reach the eastern edge of Runway 35R at the same time Aircraft Z was estimated to cross the runway threshold. Approximately 1/2-3/4 mile from the eastern edge of Runway 35R; I instructed Aircraft X to; 'go around; turn right heading 350'. Aircraft X read back the instructions correctly and complied. Aircraft Z landed without incident. Aircraft X was turned right to a 350 heading because the helicopter was crossing the departure end of Runway 35R; on track to cross over the departure end of Runway 31; en-route to the ramp. I provided Aircraft X with traffic information on the helicopter which he reported in sight. Aircraft X was instructed to; 'pass behind the helicopter; turn left and enter a left downwind for Runway 35L; Runway 35L cleared to land'. Additionally; I reiterated the same instructions two additional times which were read back correctly. I observed Aircraft X turn left and commit to a westerly heading as instructed. Aircraft Y was approximately two miles from RWY 35R threshold.I turned around to face south and visually verify that Aircraft Z had exited RWY 35R and was taxiing as instructed; observe the progress of Aircraft Y; and then turned to the west to observe the progress of the helicopter. As I was searching the left downwind to Runway 35L for Aircraft X and Aircraft Y was coming to a stop near taxiway E5; Aircraft X contacted the ATCT stating; 'Tower; there is an aircraft landing opposite direction to us'. I turned around and looked at the approach end of Runway 17L and Aircraft X had landed and was rolling out between Taxiways E3/E4. Aircraft Y contacted the ATCT and said; 'we're stopped on the runway at E5'. I informed Aircraft X that he landed Runway 17L and taxied him to parking. Once Aircraft X was off the runway; I taxied Aircraft Y to parking and then read Aircraft X the 'Brasher Notification'.Reevaluate traffic priorities and be cognizant of which aircraft require greater portions of available attention.

Data retrieved from NASA's ASRS site 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.