Narrative:

During arrival into cos from the east, we were level at 14000 ft MSL. There were numerous traffic images on the TCASII and approach (cos) was calling traffic as well. We had a TCASII resolution which said climb, climb at which time I disconnected the autoplt and initiated a climb. The resolution only lasted a few more seconds at which time, after climbing only about 100 ft, I descended back to 14000 ft and engaged the autoplt because of all the traffic. With the sun in our eyes I did not realize the autoplt did not engage right away. The aircraft descended another 200-240 ft at which time I initiated a climb back to 14000 ft. Shortly thereafter ATC (approach) descended us to 10000 ft and before reaching 10000 ft cleared us for a visual approach. My recommendation is: with the tremendous increase of traffic flow into and out of the colorado springs airport to include a significant amount of student pilot activity (military academy and others) I think it would be wise to consider an airspace change around the cos area to more restrictive. During certain time of the day in VMC conditions it is very difficult to see and be seen. At times there can be as many as 10 or more targets within a 10 mi range on the TCASII screen.

Related reports:

Google
 

Original NASA ASRS Text

Title: MLG FLC HAS TCASII ALERT WITH WHICH THEY COMPLY BUT ON RETURN TO ALT THEY DSND BELOW ASSIGNED ALT 240 FT.

Narrative: DURING ARR INTO COS FROM THE E, WE WERE LEVEL AT 14000 FT MSL. THERE WERE NUMEROUS TFC IMAGES ON THE TCASII AND APCH (COS) WAS CALLING TFC AS WELL. WE HAD A TCASII RESOLUTION WHICH SAID CLB, CLB AT WHICH TIME I DISCONNECTED THE AUTOPLT AND INITIATED A CLB. THE RESOLUTION ONLY LASTED A FEW MORE SECONDS AT WHICH TIME, AFTER CLBING ONLY ABOUT 100 FT, I DSNDED BACK TO 14000 FT AND ENGAGED THE AUTOPLT BECAUSE OF ALL THE TFC. WITH THE SUN IN OUR EYES I DID NOT REALIZE THE AUTOPLT DID NOT ENGAGE RIGHT AWAY. THE ACFT DSNDED ANOTHER 200-240 FT AT WHICH TIME I INITIATED A CLB BACK TO 14000 FT. SHORTLY THEREAFTER ATC (APCH) DSNDED US TO 10000 FT AND BEFORE REACHING 10000 FT CLRED US FOR A VISUAL APCH. MY RECOMMENDATION IS: WITH THE TREMENDOUS INCREASE OF TFC FLOW INTO AND OUT OF THE COLORADO SPRINGS ARPT TO INCLUDE A SIGNIFICANT AMOUNT OF STUDENT PLT ACTIVITY (MIL ACADEMY AND OTHERS) I THINK IT WOULD BE WISE TO CONSIDER AN AIRSPACE CHANGE AROUND THE COS AREA TO MORE RESTRICTIVE. DURING CERTAIN TIME OF THE DAY IN VMC CONDITIONS IT IS VERY DIFFICULT TO SEE AND BE SEEN. AT TIMES THERE CAN BE AS MANY AS 10 OR MORE TARGETS WITHIN A 10 MI RANGE ON THE TCASII SCREEN.

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.