PILOT ON REMOTE SENSING MISSION IN HNL CLASS B HAS CRITICAL CONFLICT WITH DASH8.

Narrative

I WAS ON A SINGLE PLT AERIAL SENSING MISSION OVER DIAMOND HEAD AND TO THE E APPROX 4 MI AT 2500 FT MSL AND WITHIN THE HNL SURFACE B AREA. PRIOR TO THE FLT; I HAD CALLED THE HCF SUPVR TO COORD THE MISSION WITHIN THE CLASS B SINCE THE AREA I INTENDED TO WORK WAS IN THE DEP CORRIDOR OF RWY 8L/R. I TOOK OFF FROM HNL LESS THAN 30 MINS EARLIER AND STAYED ON WITH THE LCL DEP CTLR. I HEARD A DASH-8 CHK IN AFTER TKOF AND HE WAS ASSIGNED A HDG AND ALT. I LOOKED BRIEFLY BUT WAS NOT ABLE TO MAKE CONTACT WITH THE DASH-8. AT THIS POINT I WAS APPROX 3 MI ESE OF THE ARPT EBOUND AT 2500 FT SO THE ARPT WAS BEHIND AND SLIGHTLY TO MY L. AS I WAS APCHING THE BEACH AT DIAMOND HEAD I HEARD THE DASH-8 SAY THEY WERE DSNDING DUE TO AN RA. I LOOKED OVER MY SHOULDER IN TIME TO SEE THE DASH-8 PASS DIRECTLY UNDER ME AND A FEW HUNDRED FT BELOW. BY THE TIME I STARTED A CLB; THE OTHER AIRPLANE HAD ALREADY PASSED. AFTER TAKING A FEW SECONDS TO COLLECT MYSELF; I CHKED MY ALTIMETER WHICH READ ABOUT 2350 FT. THE PLT OF THE DASH-8 SAID THAT THEY WERE INDICATING 200 FT OF SEPARATION. IN MY OPINION; THE CONFLICT AROSE PRIMARILY FROM MY FIXATION ON OTHER INSTS IN THE COURSE OF MY AERIAL SENSING MISSION AND NOT MAINTAINING A VISUAL LOOKOUT IN VMC. MY ATTN WAS FOCUSED ON KEEPING MY GND TRACK ON THE PRESCRIBED FLT LINE AND I DRIFTED OFF MY ALT. THE PLANE WAS FAIRLY WELL TRIMMED BUT IT WAS NOT PERFECT. I MAKE SIGNIFICANT THROTTLE ADJUSTMENTS ON EACH LINE TO KEEP MY GND SPD WITHIN THE LIMITS FOR THE SENSING EQUIP. WITH SHORT LINES AND QUICK TURNAROUNDS; I OFTEN DON'T HAVE TIME TO FINE TUNE THE ELEVATOR TRIM. ADDITIONAL FACTORS MAY HAVE BEEN THE DASH-8 PLT'S NOT MAINTAINING A VISUAL LOOKOUT IN VMC AND THE CTLR'S ASSIGNING THE DASH-8 A CONVERGING HDG. HOWEVER; HAD I MAINTAINED 2500 FT; WE WOULD HAVE HAD 500 FT OF VERT SEPARATION DURING THE XING. I PLACE THE BLAME ON MYSELF. MY BAD; LESSON LEARNED.