Narrative:

While taxiing out for departure; we were following 3 aircraft along taxiway G and transitioning to taxiway east for departure on runway 31C. The visibility was reduced to an ATIS reported 1/2 SM due to snow and freezing fog. The taxiways were all snow covered and the markings were not visible. The runway itself had been just been plowed prior to the preceding aircraft departing. The 3 aircraft ahead of us had all departed and as we approached where we believed the hold short line was to be located; the captain brought the aircraft to a stop and began to question our position in regards to the hold short line. The captain then commented that he couldn't find the hold short line. We both began searching out our windows in an attempt to find the hold short line and just a moment later we were asked by midway tower if we were holding short of runway 31C. The captain responded that we were unable to find it due to the snow covered taxiway. I also responded to tower that I thought that we had passed over it. There was an aircraft on short final who was instructed to go around. After the inbound aircraft executed its go-around; we were given takeoff clearance on runway 31C. We were never able to locate the hold short line to the runway due to the poor weather conditions but believe that we were in fact over the hold short line. I am still unsure about how far we were actually over the line though. I believe that the biggest contributing factor was the inclement weather and the snow obscuring the taxiways. Better signage and/or runway boundary lighting for the hold short areas for runway 31C. Better depiction of hold short lines on the charts. Better attention by the crew of location; especially during inclement weather.

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Original NASA ASRS Text

Title: An air carrier pilot crossed the MDW runway 31C hold short line on taxiway E in snow and freezing fog causing an aircraft on approach to go around. The runway was clear but snow covered the taxiway markings.

Narrative: While taxiing out for departure; we were following 3 aircraft along Taxiway G and transitioning to Taxiway E for departure on Runway 31C. The visibility was reduced to an ATIS reported 1/2 SM due to snow and freezing fog. The taxiways were all snow covered and the markings were not visible. The runway itself had been just been plowed prior to the preceding aircraft departing. The 3 aircraft ahead of us had all departed and as we approached where we believed the hold short line was to be located; the Captain brought the aircraft to a stop and began to question our position in regards to the hold short line. The Captain then commented that he couldn't find the hold short line. We both began searching out our windows in an attempt to find the hold short line and just a moment later we were asked by Midway Tower if we were holding short of Runway 31C. The Captain responded that we were unable to find it due to the snow covered taxiway. I also responded to Tower that I thought that we had passed over it. There was an aircraft on short final who was instructed to go around. After the inbound aircraft executed its go-around; we were given takeoff clearance on Runway 31C. We were never able to locate the hold short line to the runway due to the poor weather conditions but believe that we were in fact over the hold short line. I am still unsure about how far we were actually over the line though. I believe that the biggest contributing factor was the inclement weather and the snow obscuring the taxiways. Better signage and/or runway boundary lighting for the hold short areas for Runway 31C. Better depiction of hold short lines on the charts. Better attention by the crew of location; especially during inclement weather.

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.