Narrative:

I was the pilot flying on the first leg that landed on time. Flight was delayed a couple of hours; so I took a mid-afternoon nap before meeting captain for dinner. Our pickup was delayed 1.5 hours and the flight was delayed a total of 3 hours with a revised departure time.boarding; preflight; takeoff and en route operations were normal. Chicago weather at our arrival time was forecast to have blowing snow; 2NM visibility; winds gusting up to 24 knots out of the northwest and ceilings between 800-1500 feet. ATIS advertised arrivals to 28C; 28R and 4R at various times en route. Approach planning began an hour out with the latest ATIS advertising an ILS approach to 4R. We planned a primary approach to 4R and pulled landing data for 28C/28R in case of further changes. ATIS advertised braking action of 5-5-5 for 4R. The landing data calculation produced a 7000 foot stopping distance for good braking action with auto brakes 3 and flaps 30. Stopping distance declined to 6500 feet for auto brakes 4. We discussed both braking options. Captain initially chose AB4 while I favored AB3. He ultimately chose AB3. ATIS called the winds 34023g29 which drove a target speed of 151 knots. Tower verified the same winds at initial check-in. Engine anti-ice (ai) was on for the entire approach. Wing ai was off pending any indication of ice buildup on the forward body that did not occur. We were configured early and told to maintain 170 knots until the final marker (rekks). We were fully configured and slowed to final approach speed well before the mandated stabilized approach criteria gates. The landing was smooth and uneventful.captain used full reverse thrust and stowed the reversers passing 80 knots. He called 3000 feet runway remaining at the appropriate location and seemed to have complete control of the aircraft. At that point he asked me to disengage the auto brakes. I noted the airspeed decelerating through 70 knots and stowed the speed brakes in order to disengage the auto brakes. I expected captain to use manual braking at that point to ensure control of the aircraft as we decelerated to taxi speed. The aircraft did not decelerate like I expected between 3000 and 1000 feet remaining. At that point; I could see the end of the runway approaching rapidly and told captain that he needed to come left to exit the runway. That was when I realized that he was trying to stop the aircraft and bring it left without success. The runway end identifier and taxiway lights came up quickly at that point and we slid right as the right main gear departed the prepared surface. It took me a brief period of time to realize that the main gear had departed the prepared surface. I called O'hare tower to tell them that we had departed the runway and would not be able to clear 4R. After our situation was clarified with tower; I started the APU and shut down engine number 2.

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Original NASA ASRS Text

Title: Air carrier pilots and Dispatcher reported a runway excursion during rolling out due to 'nil' braking action. The main gear left the runway surface as the aircraft came to a rest. Passengers had to be deplaned and bussed to the terminal.

Narrative: I was the pilot flying on the first leg that landed on time. Flight was delayed a couple of hours; so I took a mid-afternoon nap before meeting Captain for dinner. Our pickup was delayed 1.5 hours and the flight was delayed a total of 3 hours with a revised departure time.Boarding; preflight; takeoff and en route operations were normal. Chicago weather at our arrival time was forecast to have blowing snow; 2NM visibility; winds gusting up to 24 knots out of the northwest and ceilings between 800-1500 feet. ATIS advertised arrivals to 28C; 28R and 4R at various times en route. Approach planning began an hour out with the latest ATIS advertising an ILS approach to 4R. We planned a primary approach to 4R and pulled landing data for 28C/28R in case of further changes. ATIS advertised braking action of 5-5-5 for 4R. The landing data calculation produced a 7000 foot stopping distance for good braking action with auto brakes 3 and flaps 30. Stopping distance declined to 6500 feet for auto brakes 4. We discussed both braking options. Captain initially chose AB4 while I favored AB3. He ultimately chose AB3. ATIS called the winds 34023G29 which drove a target speed of 151 knots. Tower verified the same winds at initial check-in. Engine Anti-Ice (AI) was on for the entire approach. Wing AI was off pending any indication of ice buildup on the forward body that did not occur. We were configured early and told to maintain 170 knots until the final marker (REKKS). We were fully configured and slowed to final approach speed well before the mandated stabilized approach criteria gates. The landing was smooth and uneventful.Captain used full reverse thrust and stowed the reversers passing 80 knots. He called 3000 feet runway remaining at the appropriate location and seemed to have complete control of the aircraft. At that point he asked me to disengage the auto brakes. I noted the airspeed decelerating through 70 knots and stowed the speed brakes in order to disengage the auto brakes. I expected Captain to use manual braking at that point to ensure control of the aircraft as we decelerated to taxi speed. The aircraft did not decelerate like I expected between 3000 and 1000 feet remaining. At that point; I could see the end of the runway approaching rapidly and told Captain that he needed to come left to exit the runway. That was when I realized that he was trying to stop the aircraft and bring it left without success. The runway end identifier and taxiway lights came up quickly at that point and we slid right as the right main gear departed the prepared surface. It took me a brief period of time to realize that the main gear had departed the prepared surface. I called O'Hare tower to tell them that we had departed the runway and would not be able to clear 4R. After our situation was clarified with tower; I started the APU and shut down engine number 2.

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.