Narrative:

I was on a mission northeast of home base ZZZ2 and was canceled while in ZZZ1 class B airspace. I notified tower of cancellation of mission and told them I would exit class B to the south and return to ZZZ2 getting my own clrncs. I switched to ZZZ2 tower and received clearance into class B airspace. I was monitoring freeway (ZZZ) unicom; but not announcing my presence. On this occasion there were 3 aircraft in the local pattern (runway was 18L traffic). I was east of the airport heading about 200 degrees approximately 7 mi from ZZZ2 when we were assigned another mission with an approximately heading of 310 degrees. I checked out with ZZZ2 and switched to TRACON to let them know I was now a priority aircraft. I had switched off ZZZ unicom in preparation for landing at ZZZ2. While checking out with ZZZ2 and checking in with TRACON; I was making a right turn approximately 3 degrees per second. During this turn; I placed my aircraft into the pattern area of ZZZ. I started the turn and the radio switches without clearing myself. I saw the C172/182(?) in my 11:30 O'clock position; approximately 150-200 ft away at my altitude. I did not have to take evasive action because I believe they already had. I went between the evading aircraft and another aircraft climbing out after takeoff. Initially; I erroneously figured I was far enough from the pattern to not impact it. I failed to consider that 3 aircraft would expand the pattern. Additionally; I started my turn for the new mission without first clearing myself. In the future I will always announce my presence; even to an empty pattern; and I will go back to one of the basics that every new pilot practices; clear your airspace! Both ZZZ2 and TRACON advised me of aircraft in the ZZZ pattern.

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Original NASA ASRS Text

Title: SA365 DAUPHIN PLT HAS AN NMAC.

Narrative: I WAS ON A MISSION NE OF HOME BASE ZZZ2 AND WAS CANCELED WHILE IN ZZZ1 CLASS B AIRSPACE. I NOTIFIED TWR OF CANCELLATION OF MISSION AND TOLD THEM I WOULD EXIT CLASS B TO THE S AND RETURN TO ZZZ2 GETTING MY OWN CLRNCS. I SWITCHED TO ZZZ2 TWR AND RECEIVED CLRNC INTO CLASS B AIRSPACE. I WAS MONITORING FREEWAY (ZZZ) UNICOM; BUT NOT ANNOUNCING MY PRESENCE. ON THIS OCCASION THERE WERE 3 ACFT IN THE LCL PATTERN (RWY WAS 18L TFC). I WAS E OF THE ARPT HDG ABOUT 200 DEGS APPROX 7 MI FROM ZZZ2 WHEN WE WERE ASSIGNED ANOTHER MISSION WITH AN APPROX HDG OF 310 DEGS. I CHKED OUT WITH ZZZ2 AND SWITCHED TO TRACON TO LET THEM KNOW I WAS NOW A PRIORITY ACFT. I HAD SWITCHED OFF ZZZ UNICOM IN PREPARATION FOR LNDG AT ZZZ2. WHILE CHKING OUT WITH ZZZ2 AND CHKING IN WITH TRACON; I WAS MAKING A R TURN APPROX 3 DEGS PER SECOND. DURING THIS TURN; I PLACED MY ACFT INTO THE PATTERN AREA OF ZZZ. I STARTED THE TURN AND THE RADIO SWITCHES WITHOUT CLRING MYSELF. I SAW THE C172/182(?) IN MY 11:30 O'CLOCK POS; APPROX 150-200 FT AWAY AT MY ALT. I DID NOT HAVE TO TAKE EVASIVE ACTION BECAUSE I BELIEVE THEY ALREADY HAD. I WENT BTWN THE EVADING ACFT AND ANOTHER ACFT CLBING OUT AFTER TKOF. INITIALLY; I ERRONEOUSLY FIGURED I WAS FAR ENOUGH FROM THE PATTERN TO NOT IMPACT IT. I FAILED TO CONSIDER THAT 3 ACFT WOULD EXPAND THE PATTERN. ADDITIONALLY; I STARTED MY TURN FOR THE NEW MISSION WITHOUT FIRST CLRING MYSELF. IN THE FUTURE I WILL ALWAYS ANNOUNCE MY PRESENCE; EVEN TO AN EMPTY PATTERN; AND I WILL GO BACK TO ONE OF THE BASICS THAT EVERY NEW PLT PRACTICES; CLR YOUR AIRSPACE! BOTH ZZZ2 AND TRACON ADVISED ME OF ACFT IN THE ZZZ PATTERN.

Data retrieved from NASA's ASRS site as of January 2009 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.