Helicopter
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3.8
Confusion; Situational Awareness
Conflict NMAC
Flight Crew Requested ATC Assistance / Clarification
Procedure; Human Factors
I approved an opposite direction ILS full stop several miles in advance. Upon first contact with the opposite direction approach I was advised by them that they wanted a touch and go followed by picking up an IFR flight plan back to their airport. During the coordination between myself; Ground Control; and TRACON several other aircraft had called inbound to the airport. I proceeded to coordinate with Ground Control to get a runway and dump all of the other traffic onto this runway to avoid opposite direction traffic. During this time another aircraft came inbound and I placed them on a right base. Additionally Aircraft X called inbound to which I approved a charted arrival for. During this time I also had a practice approach inbound that I told to enter right base. An aircraft called inbound from the North for touch and go's that I instructed to enter right downwind. I cleared Aircraft Y to land and he started his descent towards final. Moments later Aircraft X asked about an aircraft on downwind heading towards the pattern and I told him Aircraft Y was on base leg. It wasn't until it was brought to my attention two weeks later that the Aircraft X reported a NMAC on frequency. After listening to the playback I seemed to be task saturated with working complex traffic and with the poor radar coverage to the south; just completely forgot about Aircraft X inbound from the west.I have always believed this procedure to be a poorly designed one in which it allows additional holes into the SMS. We are asking helicopters to under fly aircraft in the downwind by 500 feet but placing the cross over point 1 1/2 miles past the numbers which is direct conflict with descending aircraft; or worse for base leg traffic. I would recommend to be allowed to follow old procedures.
HIO Local Controller reported a helicopter filed a NMAC while complying with an arrival procedure.