Narrative:

The weather at our destination was reported to be changing rapidly with snow; crosswinds; and low ceilings; so we were constantly monitoring the ATIS trying to keep up with the changes. As we neared the airport; we briefed the CAT2 ILS to xxr. While on the arrival; the ATIS was updated at least three times with visibilities varying from 0.5 to 1.5 miles; and crosswinds up to twenty knots requiring multiple references and modifications to the landing data. As the pilot monitoring; I was busy trying to keep up with the changes to the weather while the captain was left to fly the aircraft with less than optimal backup from me. We were vectored off the arrival and told to expect the ILS xxl. We re-briefed the approach; re-programmed the FMS; and confirmed with the ATIS that we were still within limits. As we got closer to the airport; we were given a heading of 270; which I confirmed was set correctly in the MCP; and then heard approach tell another aircraft that the RVR for xxl was 3000. I again checked the ATIS and ran the landing numbers; checking the 'RVR less than 4000' box; which revealed we were out of crosswind limits. About this time; I heard ATC ask us where we were going; and that we were supposed to be on a 270 heading. I looked back up to see the pilot flying making the turn back to 270 from a heading of approximately 350. Although I know I watched and confirmed the initial 270 heading; I cannot remember now if the aircraft actually began the turn. Because I was heads down re-evaluating the rapidly changing weather; I did not catch the deviation. ATC then told us; and the new ATIS confirmed that the visibility was 0.5 miles and we continued the approach. About twenty five miles from the runway and at 10;000 feet; we were given a heading of 310 to join and a new speed of 170. I identified the localizer on both sides. We noted that the 'runway' flag was visible on the captain's side ADI; and made a mental note of it. The first officer's side appeared normal. Shortly prior to the intercept; the flag went away; and I began to focus on my own instruments. As the CDI needle began to center on my side; I noted that the aircraft was not making a turn to intercept. Also about this time; the captain noted the return of the 'runway' flag; and began a turn back toward the localizer referencing my instruments. Again; ATC asked us about our deviation and we responded that we were returning to the course. I suggested that we switch the autopilots/navigation sources as my side appeared to be normal. With the switch in sides; the aircraft appeared to join the course normally and we elected to continue as the flags were now gone from the captain's instruments; and we were still approximately twenty miles from the field. The approach and landing were without event. Upon arrival at the gate; the captain notified maintenance regarding the flags on approachi believe that we fell into the standard trap of dividing our attention when the primary focus should have been on flying/monitoring the aircraft. With the rapid changes in weather; we were trying to be sure we were legal and safe to commence the approach. I was unable to back up the pilot flying as well as I would have liked given the necessity to keep updating the landing data and weather information. I think it might help crews during close in vectoring phases of flight if ATC would broadcast the changes to the weather; rather than stating; this would save a lot of heads down time in an already high workload environment; allowing the pilot monitoring to just verify landing data rather than getting the new ATIS via radio or ACARS first.

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Original NASA ASRS Text

Title: Excessive workload due to rapidly changing weather and runway assignments contributed to a course deviation for a B737-300 flight crew.

Narrative: The weather at our destination was reported to be changing rapidly with snow; crosswinds; and low ceilings; so we were constantly monitoring the ATIS trying to keep up with the changes. As we neared the airport; we briefed the CAT2 ILS to XXR. While on the arrival; the ATIS was updated at least three times with visibilities varying from 0.5 to 1.5 miles; and crosswinds up to twenty knots requiring multiple references and modifications to the landing data. As the pilot monitoring; I was busy trying to keep up with the changes to the weather while the Captain was left to fly the aircraft with less than optimal backup from me. We were vectored off the arrival and told to expect the ILS XXL. We re-briefed the approach; re-programmed the FMS; and confirmed with the ATIS that we were still within limits. As we got closer to the airport; we were given a heading of 270; which I confirmed was set correctly in the MCP; and then heard Approach tell another aircraft that the RVR for XXL was 3000. I again checked the ATIS and ran the landing numbers; checking the 'RVR less than 4000' box; which revealed we were out of crosswind limits. About this time; I heard ATC ask us where we were going; and that we were supposed to be on a 270 heading. I looked back up to see the pilot flying making the turn back to 270 from a heading of approximately 350. Although I know I watched and confirmed the initial 270 heading; I cannot remember now if the aircraft actually began the turn. Because I was heads down re-evaluating the rapidly changing weather; I did not catch the deviation. ATC then told us; and the new ATIS confirmed that the visibility was 0.5 miles and we continued the approach. About twenty five miles from the runway and at 10;000 feet; we were given a heading of 310 to join and a new speed of 170. I identified the localizer on both sides. We noted that the 'runway' flag was visible on the Captain's side ADI; and made a mental note of it. The First Officer's side appeared normal. Shortly prior to the intercept; the flag went away; and I began to focus on my own instruments. As the CDI needle began to center on my side; I noted that the aircraft was not making a turn to intercept. Also about this time; the Captain noted the return of the 'runway' flag; and began a turn back toward the Localizer referencing my instruments. Again; ATC asked us about our deviation and we responded that we were returning to the course. I suggested that we switch the autopilots/navigation sources as my side appeared to be normal. With the switch in sides; the aircraft appeared to join the course normally and we elected to continue as the flags were now gone from the Captain's instruments; and we were still approximately twenty miles from the field. The approach and landing were without event. Upon arrival at the gate; the Captain notified Maintenance regarding the flags on approachI believe that we fell into the standard trap of dividing our attention when the primary focus should have been on flying/monitoring the aircraft. With the rapid changes in weather; we were trying to be sure we were legal and safe to commence the approach. I was unable to back up the pilot flying as well as I would have liked given the necessity to keep updating the landing data and weather information. I think it might help crews during close in vectoring phases of flight if ATC would broadcast the changes to the weather; rather than stating; this would save a lot of heads down time in an already high workload environment; allowing the pilot monitoring to just verify landing data rather than getting the new ATIS via radio or ACARS first.

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.