Narrative:

During this flight; I was the pilot flying and captain was the pilot monitoring. We were assigned to fly the mscot 4 RNAV and as we got closer to the top of descent; we were reassigned to the drllr 5 RNAV. We planned to fly the skler transition to runway 26R as per the arrival and I briefed the ILS 26R. I believe ATC assigned several speed changes during the descent which added to the workload. I don't remember exactly when we were told to expect the RNAV rnp Y 26R but I do remember it added to our workload because I was trying to make the tight altitude and speed restrictions which I had to manage with speedbrakes. As we approached skler; we had a conversation because the RNAV was programmed correctly in the FMC but it looked different on the navigation display (nd). The nd was showing two pink navigation lines. One showed the transition from skler then a 087 track for 3.0 miles and then to drkar and on to the rest of the approach to 26R. The other pink navigation line extended from skler on an indefinite 087 track. We double checked the FMC and determined that the aircraft would fly according to the FMC. As ATC noted; it did not. After drkar; the aircraft continued on a 087 track. We caught the mistake within seconds and I began to turn the aircraft in heading select. At this time; ATC gave us a heading. I incorrectly assumed that ATC had changed plans due to their own needs but I now know that it was because our aircraft didn't follow the RNAV as assigned. This incident is indeed unfortunate but I believe that there is a discrepancy somewhere in between the drllr 5 arrival and the RNAV Y 26R.

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Original NASA ASRS Text

Title: Air carrier First Officer reported a track deviation occurred on the DRLLR5 RNAV arrival to RNAV Y 26R at IAH; and expressed the opinion that there could be a discrepancy between the DRLLR5 arrival and the RNAV Y 26R approach.

Narrative: During this flight; I was the Pilot Flying and Captain was the Pilot Monitoring. We were assigned to fly the MSCOT 4 RNAV and as we got closer to the top of descent; we were reassigned to the DRLLR 5 RNAV. We planned to fly the SKLER transition to Runway 26R as per the arrival and I briefed the ILS 26R. I believe ATC assigned several speed changes during the descent which added to the workload. I don't remember exactly when we were told to expect the RNAV RNP Y 26R but I do remember it added to our workload because I was trying to make the tight altitude and speed restrictions which I had to manage with speedbrakes. As we approached SKLER; we had a conversation because the RNAV was programmed correctly in the FMC but it looked different on the Navigation Display (ND). The ND was showing two pink navigation lines. One showed the transition from SKLER then a 087 track for 3.0 miles and then to DRKAR and on to the rest of the approach to 26R. The other pink navigation line extended from SKLER on an indefinite 087 track. We double checked the FMC and determined that the aircraft would fly according to the FMC. As ATC noted; it did not. After DRKAR; the aircraft continued on a 087 track. We caught the mistake within seconds and I began to turn the aircraft in Heading Select. At this time; ATC gave us a heading. I incorrectly assumed that ATC had changed plans due to their own needs but I now know that it was because our aircraft didn't follow the RNAV as assigned. This incident is indeed unfortunate but I believe that there is a discrepancy somewhere in between the DRLLR 5 Arrival and the RNAV Y 26R.

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.