Narrative:

Taxiing outbound; instructions were a; left on A18; D to runway 22L. Just prior to reaching where I thought A18 was; turned left onto a service road. In the turn I realized my mistake but was too late to turn back onto a. I determined best; safest course was to proceed slowly; carefully 50 ft to turn onto D. No signs or lights were struck or damaged and no aircraft damaged occurred. Ramps and taxiways (and service roads) were covered in varying degrees of ice and snow; so I was taxiing slowly to begin with; but feel that the width of plowed taxiways and the service road was the same or very similar in width. And believe snow covering the painted lines may have added to the confusion. First officer was heads down at the start of the turn getting new takeoff data (not his fault). At runway 22L holding pad received concurrence from maintenance that no damage occurred and flight continued to destination and back all ops normal. First (and last) occurrence in 20 years and will obviously be even more diligent than already am; before making turns; especially into situations from which you cannot turn back.

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Original NASA ASRS Text

Title: Captain mistakes a service road for Taxiway A18 during the aftermath of a snow storm at ORD and taxis A; service road; D to Runway 22L. No damage occurs and the aircraft is inspected by maintenance prior to departure.

Narrative: Taxiing outbound; instructions were A; left on A18; D to Runway 22L. Just prior to reaching where I thought A18 was; turned left onto a service road. In the turn I realized my mistake but was too late to turn back onto A. I determined best; safest course was to proceed slowly; carefully 50 FT to turn onto D. No signs or lights were struck or damaged and no aircraft damaged occurred. Ramps and taxiways (and service roads) were covered in varying degrees of ice and snow; so I was taxiing slowly to begin with; but feel that the width of plowed taxiways and the service road was the same or very similar in width. And believe snow covering the painted lines may have added to the confusion. First Officer was heads down at the start of the turn getting new takeoff data (not his fault). At Runway 22L holding pad received concurrence from maintenance that no damage occurred and flight continued to destination and back all ops normal. First (and last) occurrence in 20 years and will obviously be even more diligent than already am; before making turns; especially into situations from which you cannot turn back.

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.