Narrative:

While on a visual approach to runway xxc; we began to overtake a 737 who apparently had slowed early. I was hand flying and most of my attention was focused on intercepting the localizer and glide slope. We had been assigned a speed of 170 kts. Tower stated we were closing on the 737 in front of us so I asked for the gear and began to slow the aircraft immediately. As we slowed through 165 kts.; I asked for flaps 30; landing checklist and out of my periphery; I saw the captain move her hand over and move the flaps lever. During this time there was an inordinate amount of focus on the separation with the 737 in front of us and the potential for a go-around. The captain verbalized the potential for a go-around and verbalized the callouts for a go-around. There was more discussion between tower; the 737; our flight and between the captain and I regarding the separation. That's when I heard the caution tones and the master caution light up. I then asked the captain; what's the caution for. She said it was for an incomplete checklist and she didn't get the flaps all the way to 30. She moved the handle to 30; closed the checklist and I confirmed the 30 setting. I was more focused on whether the 737 was going to make the high speed and it didn't dawn on me that the checklist caution comes on at 500 ft. And we had hit criteria for an unstabilized approach. We continued the approach and I made a nice smooth landing. It wasn't until we began the debrief process that we discovered through discussion; we had actually violated SOP and the stabilized approach criteria. Usually the way unstabilized approach is presented; we describe each gate as if we are behind the airplane. As we try to catch up and meet the stabilized approach criteria prior to each 1;500 ft.; 1;000 ft. And 500 ft. Gate; we put a line in the sand to make a final decision at 500 ft. Whether to go around or continue. That was not the case in this instance. We had been 'stabilized' prior to 1;500 ft. Due to configuring early for the separation. Unfortunately; due to the distraction of a potential go around for other reasons; the stabilization was at flaps 25 and not flaps 30. Once reconfigured to flaps 30 and the problem corrected; a safe approach and landing was never in doubt. Here is an example of decision bias in full throw during a high task saturation moment. The decision bias was to go around due to an aircraft on the runway and with that fully ingrained in both my head and the captain's head; we didn't make a decision to go around for not having the flaps at 30 at 500 ft.

Related reports:

Google
 

Original NASA ASRS Text

Title: B787 First Officer reported high workload and distraction due to traffic on final that resulted in an unstabilized approach and violation of SOP.

Narrative: While on a visual approach to Runway XXC; we began to overtake a 737 who apparently had slowed early. I was hand flying and most of my attention was focused on intercepting the localizer and glide slope. We had been assigned a speed of 170 kts. Tower stated we were closing on the 737 in front of us so I asked for the gear and began to slow the aircraft immediately. As we slowed through 165 kts.; I asked for flaps 30; landing checklist and out of my periphery; I saw the Captain move her hand over and move the flaps lever. During this time there was an inordinate amount of focus on the separation with the 737 in front of us and the potential for a go-around. The Captain verbalized the potential for a go-around and verbalized the callouts for a go-around. There was more discussion between Tower; the 737; our flight and between the Captain and I regarding the separation. That's when I heard the Caution tones and the Master Caution light up. I then asked the Captain; what's the caution for. She said it was for an incomplete checklist and she didn't get the flaps all the way to 30. She moved the handle to 30; closed the checklist and I confirmed the 30 setting. I was more focused on whether the 737 was going to make the high speed and it didn't dawn on me that the checklist caution comes on at 500 ft. and we had hit criteria for an unstabilized approach. We continued the approach and I made a nice smooth landing. It wasn't until we began the debrief process that we discovered through discussion; we had actually violated SOP and the stabilized approach criteria. Usually the way unstabilized approach is presented; we describe each gate as if we are behind the airplane. As we try to catch up and meet the stabilized approach criteria prior to each 1;500 ft.; 1;000 ft. and 500 ft. gate; we put a line in the sand to make a final decision at 500 ft. whether to go around or continue. That was not the case in this instance. We had been 'stabilized' prior to 1;500 ft. due to configuring early for the separation. Unfortunately; due to the distraction of a potential go around for other reasons; the stabilization was at flaps 25 and not flaps 30. Once reconfigured to flaps 30 and the problem corrected; a safe approach and landing was never in doubt. Here is an example of decision bias in full throw during a high task saturation moment. The decision bias was to go around due to an aircraft on the runway and with that fully ingrained in both my head and the Captain's head; we didn't make a decision to go around for not having the flaps at 30 at 500 ft.

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.