A C401 PHOTO PLT ON A NO FLT PLAN FLT HAS AN INCURSION INTO CLASS A AIRSPACE AND HAS AN NMAC WITH AN ACR ACFT NE OF COS; CO.

Narrative

I WAS PERFORMING AERIAL MAPPING OF HWY 24 FROM PETERSON AFB TO CALHAN. THE ALT I WAS TRYING TO MAINTAIN FOR THIS PROJECT WAS 17900 FT MSL INDICATED. MY PLAN FOR THE FLT WAS TO REMAIN CLR OF CLASS A AIRSPACE AND AVOID FILING AN IFR FLT PLAN. I HAD RECEIVED COS LCL ATIS INFO AND SET MY ALTIMETER TO 29.68. WHILE FLYING THE PROJECT FLT LINE DOWN HWY 24; I NOTICED MY INDICATED ALT WAS REACHING FL180 AND PROMPTLY CORRECTED FOR 17900 FT MSL TO AVOID CLASS A AIRSPACE. THROUGHOUT THE WHOLE PROJECT; I WAS NOT IN COM WITH ANY CTLING AGENCY. I WAS MONITORING COS APCH. AFTER COMPLETING THE HWY 24 PROJECT I LEFT THE AREA AND DSNDED TO THE N FOR MORE WORK IN THE CENTENNIAL AREA. I CONTACTED APA TWR FOR CLRNC INTO THEIR AIRSPACE. CENTENNIAL SWITCHED ME TO 123.7. I CONTACTED THE TWR AND GAVE THEM THE INFO FOR MY SURVEY FLT AND WAS TOLD TO 'PROCEED AS REQUEST.' APA TWR CALLED FOR AN IDENT AND GAVE ME A PHONE NUMBER TO CONTACT ZDV. UPON LNDG; I CONTACTED THE WATCH SUPVR AT ZDV. HE INFORMED ME THAT I WAS OPERATING AT FL185 IN THE COS AND CAME WITHIN 100 FT OF AN AIRLINER. I TOLD HIM THAT I WAS ATTEMPTING TO REMAIN CLR OF CLASS A AIRSPACE AND SUSPECTED MY MODE C WAS IN ERROR. THE SUPVR TOLD ME MY MODE C WAS FINE BECAUSE THE IDENT AT APA WAS CORRECT; AND THE AIRLINER COULD VISUALLY TELL THAT I WAS AT FL185. THROUGHOUT THE FLT; MY INTENT WAS TO REMAIN CLR OF CLASS A AIRSPACE. IN THE FUTURE; I PLAN TO FILE AN IFR FLT PLAN FOR ANY PROJECT OVER 17000 FT MSL TO AVOID ANY POSSIBLE AIRSPACE VIOLATION.