Small Aircraft; High Wing; 1 Eng; Fixed Gear
Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 15; Flight Crew Total 1870; Flight Crew Type 560
Situational Awareness
ATC Issue All Types; Conflict NMAC
Flight Crew Took Evasive Action
Human Factors; Procedure
I was involved in a Near Mid-Air Collision (NMAC) in the Aurora State Airport; Oregon (UAO) airport traffic pattern. I immediately reported the incident to the UAO air traffic control tower (ATCT); advising them of a near miss. At the time of the incident; UAO Runway 17 was active.Prior to the incident; I was on an instrument flight plan and flying the VOR/DME-A approach into UAO. The instrument approach procedure (IAP) starts at Newburg VORTAC (UBG) and proceeds outbound along the UBG 105 radial and crosses midfield and nearly perpendicular to the UAO Runway 17/35 at 10.7 DME. At approximately 6 DME from UBG (EMILL) on the IAP; I received a handoff from Portland Approach to the ATCT; which included an advisory of traffic near the UAO airport.During the IAP; I was in and out of few to scattered clouds. Weather at UAO was VFR; to include VFR aircraft operating in the traffic pattern.Following the handoff; initially; I had an incorrect ATCT frequency set in my radio.  I believe I had set 120.15; instead of the correct frequency of 120.35. It took about 15 seconds to recognize and correct my error. Once I had the correct frequency set; I had to wait for a break in communications before I could make my initial contact with tower. I estimate my initial contact with tower occurred at about 8 DME from UBG (REYTO); which is only about 2.7 NM prior to the airport and about 1.7 NM prior to the right downwind leg to the UAO traffic pattern. I can't remember the exact words; but I was cleared by Tower for right traffic to runway 17.  The incident occurred near the intersection of the UBG 105 radial and the right downwind traffic pattern for UAO Runway 17; at near traffic pattern altitude. I passed slightly above [a small aircraft]. The aircraft passed from my right to left; consistent with a normal traffic pattern. I estimate closest point of approach to be 200 ft vertically and 200 ft horizontally. Following the incident; evasive action was taken to include a slight climb and maneuvering to increase separation and prevent a subsequent incident. I was next sequenced by tower to follow the other aircraft for landing. I'm unsure if the other aircraft noticed the near miss; I did not see any maneuvering or hear any radio calls that would indicate their awareness of the incident.The near miss could have been avoided by better situational awareness and better scanning (see and avoid) from the other aircraft; the tower controller; and myself.An earlier hand-off from Portland Approach Control to Aurora tower could have also helped prevent this near miss. Perhaps the reason for the relatively late handoff; is due to the IAP design and high terrain. Approach control may want to monitor aircraft along the IAP until they clear an area of high terrain at 6 DME from UBG (EMILL). For example; while flying at 2;200 ft between 3 and 6 DME; Approach controller advised me of a terrain alert. I could hear their alarms going off in the background of the transmission. However; 2;200 ft is the published minimum altitude for that sector of the IAP. Perhaps the IAP should be redesigned to include 2;400 ft (or higher) as the minimum altitude until reaching 6 DME. It seems to me; that IAP minimums should not be set so low as to set off ATC terrain alarms. Any change to the UAO VOR/DME-A IAP altitudes should require a change to the similar UAO RNAV (GPS)-B IAP altitudes.As a side note; the Hillsboro (HIO) VOR/DME-C IAP has some similarities with the UAO VOR/DME-A IAP. Both fly a radial from the UBG VORTAC to the near midpoint of the runway and both cover about the same distance. HIO is 10.9 NM and UAO is 10.7 NM. However; I traditionally receive the handoff from Approach Control to Tower much earlier on the HIO approach. This HIO handoff often occurs immediately after passing inbound over the UBG VORTAC. This allows for a much smoother transition with Tower.Also; UAO tower just became operational in [the last few months]. Coordination between UAO tower and Portland Approach is all brand new. I highly recommend they review their hand off procedures regarding both the VOR/DME-A and RNAV (GPS)-B IAPs; to ensure the handoff is complete well prior to reaching the airport.
Pilot reported a NMAC during an instrument approach to UAO Airport while in contact with the Local Tower Controller.