Narrative:

We were assigned and flying the eagul 6 RNAV to phx. We had been assigned runway 08 transition and were planning as such. An earlier approach controller asked us if we had preference for landing on the south side of phx. We said yes and he told us that 'runway 07R' would be on request. In order to have the FMS load a transition; we had to select runway 08. The FMS loaded the correct waypoints for the runway 08 transition and we were flying them correctly and on altitude. Shortly before the turn between queny and hiney; the controller told us to 'expect runway 07R'. Being slightly unfamiliar with phx and their specific procedures; I had misread the chart and thought that the transition for runway 07R differed from the transition for runway 08. This happened as my mind had a thought planted in it from reading the ATIS.ATIS had the guidance that 'traffic coming from the north landing runway 08; traffic from the south landing runway 07'. I inappropriately applied that comment to the eagul 6 arrival. When I looked at the arrival chart; I mistakenly applied the transitions for the west landing runways as the transition for the 'south arrivals'. When we were told to expect runway 07R; right before hiney; I was mistakenly expecting a different course and altitudes. I quickly conferred with the captain and pilot flying; asking him; do we need to continue our descent to 4;000 (the bottom altitude for the landing west transitions) or maintain the 7;000 we were almost to for the 08 transition? He incorrectly agreed that 4;000 should now be our new bottom altitude. We quickly decided to query ATC. We asked if we needed maintain the 7000; or continue for runway 07R transition. He responded with 'continue to 07R; maintain 4;000'. This let us further to believe that there should be a route change (which there wasn't); because he had confirmed the altitude we were expecting.I then loaded runway 07R into the FMS. This caused a new set of problems as the FMC reloaded the runway 08/07R/07L transition by placing homrr behind us in the legs page and adding a discontinuity after homrr. This essentially cancelled the ability of the FMS to navigate the airplane. I began searching for the incorrect waypoints (for the wrong transition) they weren't there. The same waypoints we had been flying were now in 'front of us' in the FMS; simply behind the discontinuity. Preoccupied by the FMS confusion; the aircraft FMS entered 'roll mode' (essentially a wings level attitude) and departed the depicted STAR route. This caused the aircraft to be off course and not turn towards obase; which should have been a flyover waypoint. The pilot flying disconnected the autopilot and began a turn as soon as it was recognized by the pilot not flying that something was incorrect. He initiated a turn towards obase. At about this time; ATC assigned a heading (270 degrees) and vectored us in to runway 07R. No deviations or loss of separations were mentioned by ATC and the flight was completed uneventfully.corrective actions should include a better understanding of the RNAV arrival chart; and not making assumptions on incorrect conclusions about the arrivals. A better review of the chart; and less mental mistakes; would have prevented the error. Familiarity with the airport would also improve the situational awareness. In houston; some of the RNAV arrivals have transitions specific to each runway. As a safeguard; it would be better not to make the runway change in the FMS until it is known that the aircraft will be on the right path. In this case; delaying the change until after the turn at hiney.

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Original NASA ASRS Text

Title: During descent into PHX; a runway change lead to anomalies in the FMC navigation process in compliance with the published RNAV arrival.

Narrative: We were assigned and flying the EAGUL 6 RNAV to PHX. We had been assigned Runway 08 transition and were planning as such. An earlier approach controller asked us if we had preference for landing on the south side of PHX. We said yes and he told us that 'RWY 07R' would be on request. In order to have the FMS load a transition; we had to select RWY 08. The FMS loaded the correct waypoints for the RWY 08 transition and we were flying them correctly and on altitude. Shortly before the turn between QUENY and HINEY; the controller told us to 'expect RWY 07R'. Being slightly unfamiliar with PHX and their specific procedures; I had misread the chart and thought that the Transition for RWY 07R differed from the transition for RWY 08. This happened as my mind had a thought planted in it from reading the ATIS.ATIS had the guidance that 'Traffic coming from the NORTH landing runway 08; traffic from the south landing RWY 07'. I inappropriately applied that comment to the EAGUL 6 arrival. When I looked at the Arrival chart; I mistakenly applied the transitions for the west landing runways as the transition for the 'south arrivals'. When we were told to expect RWY 07R; right before HINEY; I was mistakenly expecting a different course and altitudes. I quickly conferred with the captain and Pilot Flying; asking him; do we need to continue our descent to 4;000 (the bottom altitude for the landing west transitions) or maintain the 7;000 we were almost to for the 08 transition? He incorrectly agreed that 4;000 should now be our new bottom altitude. We quickly decided to query ATC. We asked if we needed maintain the 7000; or continue for RWY 07R transition. He responded with 'continue to 07R; maintain 4;000'. This let us further to believe that there should be a route change (which there wasn't); because he had confirmed the altitude we were expecting.I then loaded RWY 07R into the FMS. This caused a new set of problems as the FMC reloaded the RWY 08/07R/07L transition by placing HOMRR behind us in the legs page and adding a discontinuity after HOMRR. This essentially cancelled the ability of the FMS to navigate the airplane. I began searching for the incorrect waypoints (for the wrong transition) they weren't there. The same waypoints we had been flying were now in 'front of us' in the FMS; simply behind the discontinuity. Preoccupied by the FMS confusion; the aircraft FMS entered 'roll mode' (essentially a wings level attitude) and departed the depicted STAR route. This caused the aircraft to be off course and not turn towards OBASE; which should have been a flyover waypoint. The pilot flying disconnected the autopilot and began a turn as soon as it was recognized by the pilot not flying that something was incorrect. He initiated a turn towards OBASE. At about this time; ATC assigned a heading (270 degrees) and vectored us in to RWY 07R. No deviations or loss of separations were mentioned by ATC and the flight was completed uneventfully.Corrective actions should include a better understanding of the RNAV arrival chart; and not making assumptions on incorrect conclusions about the arrivals. A better review of the chart; and less mental mistakes; would have prevented the error. Familiarity with the airport would also improve the situational awareness. In Houston; some of the RNAV arrivals have transitions specific to each runway. As a safeguard; it would be better not to make the runway change in the FMS until it is known that the aircraft will be on the right path. In this case; delaying the change until after the turn at HINEY.

Data retrieved from NASA's ASRS site 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.