HELI IN PRACTICE AREA EXPERIENCED NMAC NEAR NON TWR ARPT.

Narrative

LONGMONT HAS HELI PRACTICE AREA THAT A LCL OPERATOR ESTABLISHED. WAS WORKING IN THAT AREA AND ON THE ARPT BOUNDARY. AT THE BOUNDARY; THERE IS AN IRRIGATION XING THAT IS GOOD FOR PINNACLE LNDGS AND SLOPE LNDGS. NORMAL RADIO CALLS FOR POS AND POSITIONING WERE MADE. HAD 1 CESSNA SEE IN THE LCL PATTERN FOR FAVORED RWY 29. EXPERIMENTAL ACFT (SEL) MADE NORMAL TKOF TO W. SHORTLY; THE EXPERIMENTAL ACFT CALLED IN AND WOULD BE MAKING A LNDG 'IN THE GRASS;' RWY 11. I HAD THE CESSNA AND I INITIALLY HAD THE OPPOSITE DIRECTION EXPERIMENTAL. I WAS BTWN 30-20 FT APCHING THE PINNACLE WHERE I REALIZED THE EXPERIMENTAL ACFT WAS AT MY 11:30 O'CLOCK POS; AT OR NEAR MY ALT. THE EXPERIMENTAL DID A GAR AND I BROKE OFF THE APCH AS WELL. LONGMONT HAS A TURF RWY; BUT THE EXPERIMENTAL WAS LNDG ON AN UNIMPROVED AREA WELL S OF THE TURF RWY. I WAS OPERATING IN AN AREA THAT SHOULD HAVE BEEN WELL CLR. I OBVIOUSLY LOST SIGHT OF THE EXPERIMENTAL AND I BELIEVED THAT THEY WOULD BE USING THE TURF STRIP. INVALID ASSUMPTIONS! AS SOON AS THE EXPERIMENTAL DECIDED TO GO OPPOSITE DIRECTION; I SHOULD HAVE BEEN MORE ALERT. I WAS IN A LOW ALT; HIGH WORKLOAD OP AND WAS SURPRISED BY THE NON STANDARD AIRPLANE OP.