Small aircraft at cruise has near midair collision with medium large transport climbing.

Attributes
ACN	239716
Time
Date	199304
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : cos
State Reference	CO
Altitude	msl bound lower : 11200 msl bound upper : 11500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cos
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	None
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 35 flight time total : 1200 flight time type : 500
ASRS Report	239716
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	other controllera
Resolutory Action	other other
Consequence	Other
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was in contact with cos approach when I was notified of traffic. At time of notice to conflicting traffic was less than 1/4 mi and reporting 11200 ft and climbing. The conflicting traffic was, I believe, an medium large transport. I do not believe he was aware or had any warning of my presence until I was warned of traffic conflict. The controller was busy with another plane that appeared to have transponder trouble immediately preceding the warning comment. He immediately returned to the other aircraft upon issuing the warning and continued working with transponder problem. The other aircraft, medium large transport, expressed concern to controller upon 'near miss' with no comment from ATC. My altitude was 11500 ft and verified by ATC. I was level at said altitude for approximately 5-8 mins prior to incident.

Original NASA ASRS Text

Title: SMA AT CRUISE HAS NMAC WITH MLG CLBING.

Narrative: I WAS IN CONTACT WITH COS APCH WHEN I WAS NOTIFIED OF TFC. AT TIME OF NOTICE TO CONFLICTING TFC WAS LESS THAN 1/4 MI AND RPTING 11200 FT AND CLBING. THE CONFLICTING TFC WAS, I BELIEVE, AN MLG. I DO NOT BELIEVE HE WAS AWARE OR HAD ANY WARNING OF MY PRESENCE UNTIL I WAS WARNED OF TFC CONFLICT. THE CTLR WAS BUSY WITH ANOTHER PLANE THAT APPEARED TO HAVE XPONDER TROUBLE IMMEDIATELY PRECEDING THE WARNING COMMENT. HE IMMEDIATELY RETURNED TO THE OTHER ACFT UPON ISSUING THE WARNING AND CONTINUED WORKING WITH XPONDER PROB. THE OTHER ACFT, MLG, EXPRESSED CONCERN TO CTLR UPON 'NEAR MISS' WITH NO COMMENT FROM ATC. MY ALT WAS 11500 FT AND VERIFIED BY ATC. I WAS LEVEL AT SAID ALT FOR APPROX 5-8 MINS PRIOR TO INCIDENT.

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.