Narrative:

Arriving at lmo from the southwest; fit in perfectly with entry into the VFR pattern; 45 degrees to the downwind; landing runway 29. Already at pattern altitude; showing landing lights to enhance the chance of being seen. Had been monitoring unicom for several minutes; trying to keep track of several aircraft in the area and pattern. Had been announcing my position and intentions about every 2 miles. Just prior to turning right onto the downwind another single engine high-wing appeared in the windscreen; quite close. Impression from memory was that the other plane was approaching almost head-on from below and slightly to my left. However; it happened so fast the precise details are uncertain. Conflicting traffic was moving from left to right across my windscreen. An instant later the other plane was in a climbing left turn. My evasive action was a sharp left turn. I passed behind the other plane; entered the downwind; and landed in sequence. Lost contact with the other plane immediately after the incident. Questions; possibilities; and other factors: 1) I had not previously identified the other plane from traffic announcement heard on unicom. Nor had I spotted it visually although I was keeping a close watch. 2) had the other plane just departing lmo runway 29 and was remaining in the patter or (more likely) was departing in a climb to the south? Unknown. 3) one of the several other planes in the area/pattern was a twin being used to carry parachute jumpers aloft for jumps directly over the airport. That plane was entering the pattern from above (as it typically does) ahead of me at the time of our arrival. Trying to keep visual contact with that plane could have been a distraction factor. 4) very unlikely the other pilot saw me; certainly not until the very last moment. Was his turn an evasive maneuver or just a climb left turn to the east? 5) the encounter was close enough it could easily have had a bad outcome. 6) reemphasizes the need to keep especially good visual watch at a busy non-tower airport; as well as making and paying close attention to traffic calls on unicom; and the skydiving airplane is definitely a factor at lmo.

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Original NASA ASRS Text

Title: C182 pilot joining the traffic pattern on the 45 at LMO experienced a NMAC with another Cessna turning downwind or departing.

Narrative: Arriving at LMO from the southwest; fit in perfectly with entry into the VFR pattern; 45 degrees to the downwind; landing Runway 29. Already at pattern altitude; showing landing lights to enhance the chance of being seen. Had been monitoring UNICOM for several minutes; trying to keep track of several aircraft in the area and pattern. Had been announcing my position and intentions about every 2 miles. Just prior to turning right onto the downwind another single engine high-wing appeared in the windscreen; quite close. Impression from memory was that the other plane was approaching almost head-on from below and slightly to my left. However; it happened so fast the precise details are uncertain. Conflicting traffic was moving from left to right across my windscreen. An instant later the other plane was in a climbing left turn. My evasive action was a sharp left turn. I passed behind the other plane; entered the downwind; and landed in sequence. Lost contact with the other plane immediately after the incident. Questions; possibilities; and other factors: 1) I had not previously identified the other plane from traffic announcement heard on UNICOM. Nor had I spotted it visually although I was keeping a close watch. 2) Had the other plane just departing LMO Runway 29 and was remaining in the patter or (more likely) was departing in a climb to the south? Unknown. 3) One of the several other planes in the area/pattern was a twin being used to carry parachute jumpers aloft for jumps directly over the airport. That plane was entering the pattern from above (as it typically does) ahead of me at the time of our arrival. Trying to keep visual contact with that plane could have been a distraction factor. 4) Very unlikely the other pilot saw me; certainly not until the very last moment. Was his turn an evasive maneuver or just a climb left turn to the East? 5) The encounter was close enough it could easily have had a bad outcome. 6) Reemphasizes the need to keep especially good visual watch at a busy non-tower airport; as well as making and paying close attention to traffic calls on UNICOM; and the skydiving airplane is definitely a factor at LMO.

Data retrieved from NASA's ASRS site as of April 2012 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.