Narrative:

On a flight to sac; I approached the airport from the south west; passing 1 NM west of the sac VOR. On initial call up; I recall tower instructing me to enter right traffic for runway 20 and report downwind. I maneuvered to enter the standard left pattern for runway 20. While entering downwind; I noticed a departing aircraft making a left crosswind turn. I notified tower and requested a right 360 as it appeared that this would keep me clear of the aircraft's path on crosswind. Tower asked who was requesting a right 360. Once tower understood who and where I was; tower asked if the departing aircraft had me in sight (they did) and advised that I continue on downwind in the left pattern. The departing aircraft passed behind me below my altitude. A contributing factor to this event was the lack of terminal radar services; this was announced on ATIS. It was also a busy time; with multiple aircraft arriving and departing; including two aircraft in the pattern. While briefing myself for the approach after picking up ATIS; I reviewed the standard pattern for the runway in use; 20. The standard pattern is left traffic. On a flight with my instructor to this airport; I had made the mistake of thinking I was to enter right traffic; when in fact at this earlier time I was instructed by tower to enter left traffic. In reviewing the pattern information; I created a sense of certainty about what to expect; to the degree that I believe I read back tower's instruction to enter right traffic without realizing the conflict with what I was expecting and changing my mental plan for the approach to match tower's instruction. Since I thought tower's instructions matched what I expected; I didn't write them down. Due to the lack of radar I placed a greater emphasis on looking out for other traffic; perhaps to the extent that I mentally moved on too quickly after tower's pattern instruction. While reviewing standard approach information and being prepared for what is likely to come is always a good thing to do; I will go one step further in the future to include alternatives; such as 'what if I'm not assigned standard traffic; what will I do?'. Given my position on initial call up; perhaps I should have anticipated that tower would give me right traffic to decrease the distance traveled for pattern entry. I will try to write down ATC instructions; even when they match what I expect and are something I think I can remember. Had I written down the instruction; I might have caught my error by doing so.

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Original NASA ASRS Text

Title: A low time small aircraft pilot entered the SAC Runway 20 traffic pattern incorrectly because his mental model of how the traffic pattern was constructed did not fit ATC's instructions.

Narrative: On a flight to SAC; I approached the airport from the south west; passing 1 NM west of the SAC VOR. On initial call up; I recall Tower instructing me to enter right traffic for Runway 20 and report downwind. I maneuvered to enter the standard left pattern for Runway 20. While entering downwind; I noticed a departing aircraft making a left crosswind turn. I notified Tower and requested a right 360 as it appeared that this would keep me clear of the aircraft's path on crosswind. Tower asked who was requesting a right 360. Once Tower understood who and where I was; Tower asked if the departing aircraft had me in sight (they did) and advised that I continue on downwind in the left pattern. The departing aircraft passed behind me below my altitude. A contributing factor to this event was the lack of terminal radar services; this was announced on ATIS. It was also a busy time; with multiple aircraft arriving and departing; including two aircraft in the pattern. While briefing myself for the approach after picking up ATIS; I reviewed the standard pattern for the Runway in use; 20. The standard pattern is left traffic. On a flight with my instructor to this airport; I had made the mistake of thinking I was to enter right traffic; when in fact at this earlier time I was instructed by Tower to enter left traffic. In reviewing the pattern information; I created a sense of certainty about what to expect; to the degree that I believe I read back Tower's instruction to enter right traffic without realizing the conflict with what I was expecting and changing my mental plan for the approach to match Tower's instruction. Since I thought Tower's instructions matched what I expected; I didn't write them down. Due to the lack of radar I placed a greater emphasis on looking out for other traffic; perhaps to the extent that I mentally moved on too quickly after Tower's pattern instruction. While reviewing standard approach information and being prepared for what is likely to come is always a good thing to do; I will go one step further in the future to include alternatives; such as 'what if I'm not assigned standard traffic; what will I do?'. Given my position on initial call up; perhaps I should have anticipated that Tower would give me right traffic to decrease the distance traveled for pattern entry. I will try to write down ATC instructions; even when they match what I expect and are something I think I can remember. Had I written down the instruction; I might have caught my error by doing so.

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.