Narrative:

I was inbound to ksql from the woodside VOR and cleared by ksql tower to cross over the airport and report at 1200 feet. Runway 30 with a right traffic pattern was in use as usual. Just prior to reaching the airport; I was advised of helicopter traffic crossing under me right to left; which I had in sight and acknowledged. I was not made aware that this traffic was in the frequently-used non-standard left traffic pattern used for helicopter training. Immediately after my traffic acknowledgment I was given the instruction 'enter downwind'. Or at least; that is what I heard. It is possible that I was told 'continue downwind'; but I was most certainly not told 'extend your downwind and we will call your base turn'; which is a fairly common occurrence at this busy airport. I took the instruction to mean 'enter the downwind leg as soon as possible from your current position'; which is normal for the direction from which I was entering. I entered the downwind leg fairly close-in to the airport and was simultaneously descending and slowing the aircraft. Once past the numbers; I observed another high-wing cessna on final; waited until I was well past it; and executed my base turn; which due to my proximity to the extended centerline was immediately followed by a turn to final. At this point; I was also nearing the kpao airspace to the south; so a turn would be necessary shortly in order to avoid their airspace anyway. The helicopter asked if they were cleared to land; and was told by tower to 'follow the cessna on final; oh no; the other cessna on final behind... He's cut in front of you.' I looked to my left for the helicopter; and saw it close by on a converging course but above and behind me and descending rapidly from much higher than I'd been on my base turn. While I had the helicopter in sight; the helicopter pilot acknowledged seeing the first cessna and then acknowledged seeing me. I was then cleared to land; but admonished by the tower to; in the future; not turn base until instructed. Because I saw another aircraft on the runway ahead; and because I wanted to get reoriented; I elected to go around and landed uneventfully the next time around. This situation resulted from a variety of factors. 1) I was not made aware that the helicopter traffic was in fact in the non-standard opposite-side pattern and I assumed that it was simply passing through the airspace along the freeway. 2) because of #1; I was not looking for a helicopter on the far side of the traffic pattern which might be entering left base as I was entering right base. 3) the helicopter approach angle is significantly steeper than an airplane approach angle; so I did not see a helicopter abeam my position from my high-wing aircraft while on downwind or when starting my base turn. 4) the tower did not use phraseology in this case (though they often do) to clearly indicate that they were expecting me to continue flying downwind until the helicopter traffic had joined the final approach path 5) the tower did not advise me of the helicopter traffic at any time after it had passed beneath me and into a position I could not continue to monitor; 6) the tower did not provide me with sequence information (e.g.; 'you are number 3 after the helicopter') which would have alerted me as to the tower's intended landing sequence.in the future; the this conflict could be avoided if 1) the ATIS specifically mentioned the simultaneous use of a left traffic pattern for helicopter operations to remind pilots of this possibility 2) the tower clearly states every time they are expecting the base turn to be delayed (as they typically do by saying 'extend your downwind and we will call your base turn'); 3) the tower provides pilots with sequence information as early as possible (e.g.; 'enter downwind; you are #4 after a helicopter'); 4) all pilots; including myself; request explicit clearance to make the base turn prior to executing the turn. Because of the steep approach angle ofthe helicopter and the high-wing configuration of my aircraft; the 5th suggestion -- 'visually verify that there are no helicopters entering from the other side' -- is unfortunately not possible to implement. This could also be avoided by requiring helicopters to use the same traffic pattern when landing on the same runway; but I understand that this would complicate operations in other ways.

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Original NASA ASRS Text

Title: A Cessna 177R had a close encounter with an R22 helicopter in the traffic pattern.

Narrative: I was inbound to KSQL from the Woodside VOR and cleared by KSQL tower to cross over the airport and report at 1200 feet. Runway 30 with a right traffic pattern was in use as usual. Just prior to reaching the airport; I was advised of helicopter traffic crossing under me right to left; which I had in sight and acknowledged. I was not made aware that this traffic was in the frequently-used non-standard left traffic pattern used for helicopter training. Immediately after my traffic acknowledgment I was given the instruction 'enter downwind'. Or at least; that is what I heard. It is possible that I was told 'continue downwind'; but I was most certainly NOT told 'extend your downwind and we will call your base turn'; which is a fairly common occurrence at this busy airport. I took the instruction to mean 'enter the downwind leg as soon as possible from your current position'; which is normal for the direction from which I was entering. I entered the downwind leg fairly close-in to the airport and was simultaneously descending and slowing the aircraft. Once past the numbers; I observed another high-wing Cessna on final; waited until I was well past it; and executed my base turn; which due to my proximity to the extended centerline was immediately followed by a turn to final. At this point; I was also nearing the KPAO airspace to the south; so a turn would be necessary shortly in order to avoid their airspace anyway. The helicopter asked if they were cleared to land; and was told by tower to 'follow the Cessna on final; oh no; the other Cessna on final behind... He's cut in front of you.' I looked to my left for the helicopter; and saw it close by on a converging course but above and behind me and descending rapidly from much higher than I'd been on my base turn. While I had the helicopter in sight; the helicopter pilot acknowledged seeing the first Cessna and then acknowledged seeing me. I was then cleared to land; but admonished by the tower to; in the future; not turn base until instructed. Because I saw another aircraft on the runway ahead; and because I wanted to get reoriented; I elected to go around and landed uneventfully the next time around. This situation resulted from a variety of factors. 1) I was not made aware that the helicopter traffic was in fact in the non-standard opposite-side pattern and I assumed that it was simply passing through the airspace along the freeway. 2) Because of #1; I was not looking for a helicopter on the far side of the traffic pattern which might be entering left base as I was entering right base. 3) The helicopter approach angle is significantly steeper than an airplane approach angle; so I did not see a helicopter abeam my position from my high-wing aircraft while on downwind or when starting my base turn. 4) The Tower did not use phraseology in this case (though they often do) to clearly indicate that they were expecting me to continue flying downwind until the helicopter traffic had joined the final approach path 5) The tower did not advise me of the helicopter traffic at any time after it had passed beneath me and into a position I could not continue to monitor; 6) The tower did not provide me with sequence information (e.g.; 'you are number 3 after the helicopter') which would have alerted me as to the tower's intended landing sequence.In the future; the this conflict could be avoided if 1) The ATIS specifically mentioned the simultaneous use of a left traffic pattern for helicopter operations to remind pilots of this possibility 2) The tower clearly states EVERY TIME they are expecting the base turn to be delayed (as they typically do by saying 'extend your downwind and we will call your base turn'); 3) The tower provides pilots with sequence information as early as possible (e.g.; 'enter downwind; you are #4 after a helicopter'); 4) All pilots; including myself; request explicit clearance to make the base turn prior to executing the turn. Because of the steep approach angle ofthe helicopter and the high-wing configuration of my aircraft; the 5th suggestion -- 'visually verify that there are no helicopters entering from the other side' -- is unfortunately not possible to implement. This could also be avoided by requiring helicopters to use the same traffic pattern when landing on the same runway; but I understand that this would complicate operations in other ways.

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.