Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) .7
Communication Breakdown
ATC Issue All Types; Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Aircraft; Human Factors; Procedure
A Light Sport aircraft inbound on Campbell Arrival [receiving] radar advisories with A11.  Instructed to enter left base Runway 25. A Piper Aztec departed Runway 25 on Campbell Departure.  Traffic was not issued with the Aztec's takeoff clearance because the Light Sport was over Campbell airstrip 110 knots on the Campbell arrival and should not have been a conflict for the Aztec per the lateral separation provided by the Campbell Departure.  A radar replay showed that the Light Sport did not fly the Campbell Arrival correctly.  From Campbell airstrip he overflew Tudor Bus Barn to Providence Hospital putting him in conflict with the Aztec outbound via Tudor Bus Barn on Campbell Departure.  If he had flown the Campbell Arrival to the left base 25 over Boniface as depicted; there would not have been a conflict.  Aircraft reported inbound from the northwest; and A11 called on the land line regarding that aircraft.  I relayed Approach's information to the pilot and issued traffic for another aircraft inbound from the northwest.  I did not return my scan back to the south until the Light Sport and the Aztec passed; at which time the Light Sport reported NMAC.  The Aztec was still on frequency and stated; 'It was not that close.'Pilot forum explaining the imperativeness of flying arrival/departure procedures precisely.  Maybe using radar replays or flight simulator depictions.
MRI Controller reports of an aircraft that is supposed to follow a route into the airport and does not; while a departure reports having a NMAC with the arriving aircraft. Routes would have been separated if the arrival was following the prescribed route.