Narrative:

I was departing koa from runway 17 departure full length. At 3/4 length runway length, still on runway heading, I turned crosswind at 400 ft AGL. Koa tower came on 120.3 and reported to a robinson helicopter entering the pattern on a left downwind (I was on a left turnout) that I was departing and to look for me. This was the first I heard from tower that another aircraft was in the pattern and I had seen no one else near the airport when I lined up for departure. When I heard tower talk to the helicopter I looked for him and he was taking evasive left turn and I took evasive left turn because we were both at approximately 500 ft AGL. I told tower that I had traffic in sight and that that was a close call. The helicopter never said anything. The tower then told me that I should have notified them that I was going to make an early left turn for downwind departure. I felt that the tower should have told me of the other traffic prior to departure so I would have known to be looking. I also know that I should have stayed on runway heading until departure runways 35 had been made and then have initiated my turnout. Regardless of altitude, it is extremely important to maintain runway heading until end of runway before turning crosswind. It is also extremely important to absolutely clear the pattern on takeoff visually so near misses will never be a factor. I fault myself for both of my mistakes and am thankful to learn from them.

Related reports:

Google
 

Original NASA ASRS Text

Title: NMAC. TFC PATTERN DEV.

Narrative: I WAS DEPARTING KOA FROM RWY 17 DEP FULL LENGTH. AT 3/4 LENGTH RWY LENGTH, STILL ON RWY HDG, I TURNED XWIND AT 400 FT AGL. KOA TWR CAME ON 120.3 AND RPTED TO A ROBINSON HELI ENTERING THE PATTERN ON A L DOWNWIND (I WAS ON A L TURNOUT) THAT I WAS DEPARTING AND TO LOOK FOR ME. THIS WAS THE FIRST I HEARD FROM TWR THAT ANOTHER ACFT WAS IN THE PATTERN AND I HAD SEEN NO ONE ELSE NEAR THE ARPT WHEN I LINED UP FOR DEP. WHEN I HEARD TWR TALK TO THE HELI I LOOKED FOR HIM AND HE WAS TAKING EVASIVE L TURN AND I TOOK EVASIVE L TURN BECAUSE WE WERE BOTH AT APPROX 500 FT AGL. I TOLD TWR THAT I HAD TFC IN SIGHT AND THAT THAT WAS A CLOSE CALL. THE HELI NEVER SAID ANYTHING. THE TWR THEN TOLD ME THAT I SHOULD HAVE NOTIFIED THEM THAT I WAS GOING TO MAKE AN EARLY L TURN FOR DOWNWIND DEP. I FELT THAT THE TWR SHOULD HAVE TOLD ME OF THE OTHER TFC PRIOR TO DEP SO I WOULD HAVE KNOWN TO BE LOOKING. I ALSO KNOW THAT I SHOULD HAVE STAYED ON RWY HDG UNTIL DEP RWYS 35 HAD BEEN MADE AND THEN HAVE INITIATED MY TURNOUT. REGARDLESS OF ALT, IT IS EXTREMELY IMPORTANT TO MAINTAIN RWY HDG UNTIL END OF RWY BEFORE TURNING XWIND. IT IS ALSO EXTREMELY IMPORTANT TO ABSOLUTELY CLR THE PATTERN ON TKOF VISUALLY SO NEAR MISSES WILL NEVER BE A FACTOR. I FAULT MYSELF FOR BOTH OF MY MISTAKES AND AM THANKFUL TO LEARN FROM THEM.

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.