Narrative:

We were level at 3;000 flying base vectors for the ILS runway 5R at ind. We were given at turn to intercept and cleared for approach at or above 2;500 MSL. We started the turn; but I did not arm the approach. Just as it was apparent we were going to not intercept; the pilot monitoring mentioned I needed to arm the approach. I adjusted the heading to avoid overshoot; but we still ended up overshooting. The approach controller gave just a heading to again intercept. I had the localizer armed; but neglected to arm approach. This time; we did intercept; but since I had only pushed localizer; we were not descending and were high on the approach. When we realized this; I disengaged the autopilot and tried to increase descent with speed brake. Our configuration was gear down; flaps 20; with speed brake out. Our sink rate caused the GPWS to call out 'sink rate.' we decided to initiate a go-around; as we were not going to be stable. Tower asked us our reason and we told them we were not stable. The controller said no problem and had us continue to 3;000 and handed us back to approach. We were vectored back around and fly the same 5R approach and landed. As pilot flying; I did not arm the approach when cleared. This started a chain of errors which included me then only arming localizer when again; I should have armed approach. One factor that did distract us was the ATC radios as we arrived in the 25 NM area of ind. It was extremely busy and many were given vectors off the gibbs arrival; only to be directed back to knight. There were a couple aircraft who received runway changes and another aircraft who answered instructions that were not meant for them. I really got engulfed trying to figure out how our aircraft was going to work in the sequence. I let this distract me too much from also focusing on flying the aircraft correctly (i.e.; get cleared and arm the approach mode).don't forget basic procedures like arming the approach when cleared and in a position to intercept localizer course.

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Original NASA ASRS Text

Title: Air carrier flight crew reported executing a go-around after the approach became unstabilized following failure to arm the approach mode.

Narrative: We were level at 3;000 flying base vectors for the ILS RWY 5R at IND. We were given at turn to intercept and cleared for approach at or above 2;500 MSL. We started the turn; but I did not arm the approach. Just as it was apparent we were going to not intercept; the Pilot Monitoring mentioned I needed to arm the approach. I adjusted the heading to avoid overshoot; but we still ended up overshooting. The Approach Controller gave just a heading to again intercept. I had the LOC armed; but neglected to arm approach. This time; we did intercept; but since I had only pushed LOC; we were not descending and were high on the approach. When we realized this; I disengaged the autopilot and tried to increase descent with speed brake. Our configuration was gear down; flaps 20; with speed brake out. Our sink rate caused the GPWS to call out 'sink rate.' We decided to initiate a go-around; as we were not going to be stable. Tower asked us our reason and we told them we were not stable. The Controller said no problem and had us continue to 3;000 and handed us back to Approach. We were vectored back around and fly the same 5R approach and landed. As Pilot Flying; I did not arm the Approach when cleared. This started a chain of errors which included me then only arming LOC when again; I should have armed Approach. One factor that did distract us was the ATC radios as we arrived in the 25 NM area of IND. It was extremely busy and many were given vectors off the GIBBS arrival; only to be directed back to Knight. There were a couple aircraft who received runway changes and another aircraft who answered instructions that were not meant for them. I really got engulfed trying to figure out how our aircraft was going to work in the sequence. I let this distract me too much from also focusing on flying the aircraft correctly (i.e.; get cleared and arm the Approach mode).Don't forget basic procedures like arming the approach when cleared and in a position to intercept localizer course.

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.