Date: 202102
Local time of day: 0601-1200
Location: ORD.Airport, IL
Flight conditions: VMC
Weather elements / visibility: Rain
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Airspace: Class B ORD
ATC / advisory: Ramp ORD
Aircraft component: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Communication Breakdown
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Ground Event / Encounter Ground Equipment Issue; Ground Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control
Contributing factors: Airport; Procedure; Weather
Primary problem: Procedure

Narrative: After arrival [at] ORD Flight Attendant advises door 2L has been disarmed but the slide armed light was still illuminated. ELB report of write up was sent and maintenance was verbally advised. Station operations and ramp control advised of irregular door situation. Jet bridge was unsuccessfully re-positioned to remove passengers via door 1L. Idea to taxi aircraft to [gate] was rejected after Captain consulted maintenance and MRD was broken therefore pushback unauthorized. Move team was called to tow aircraft. Duty Manager was contacted for authorization. Move team plugged headset into aircraft and plan was discussed on towing aircraft to [gate]. Pilots ran all normal checklists and consulted QRH tow in supplementary procedure. Move team advised pilots he would be providing all Ramp and ATC communications. He also stated that after he commanded the pilots to release parking brake he would need to disconnect headset with no further communications available until reaching [gate]. After parking aircraft at [gate] he would re plug in headset and advise pilot to set parking brake. As aircraft approached [gate] ramp area was covered with ice and snow. Digital sign read slippery conditions. Braking action appeared to be poor. Aircraft was brought to a stop. Captain was unsure if towing was complete; tug was sliding in slippery conditions or another white tug that was parked in front of aircraft was an obstruction. After a few seconds aircraft began to move forward again at the same feel; rate and speed as under tow. Soon mechanics were seen on both sides of the aircraft frantically giving the set parking brake signal. Both Captain and First Officer immediately and simultaneously pushed down brake pedals. Captain then set parking brake. Move team plugged in headset. Captain asked the question what happened? Move team replied they followed their correct procedures which was to chock main tires; disconnect tug; and they were in the process of chocking nose gear and plugging in headset when the aircraft jumped the main chocks and began uncommanded aircraft movement towards the terminal of approximately 10 ft forward lasting several seconds. Weight of aircraft was approximately 217;000 lbs. Aircraft made no contact with any person; jet bridge or equipment.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air Carrier flight crew reported while ground crew was repositioning aircraft in snow and ice; there was loss of aircraft control.