Pilots reported a taxiway excursion at MKE airport due to poor lighting and charting.
Synopsis
Pilots reported a taxiway excursion at MKE airport due to poor lighting and charting.
Narrative
Pushed back from Gate XX in MKE at XA:59 in nighttime conditions. Received clearance from Ground Control to taxi to the West Deice Pad via Taxiways B and V. Confirmed the clearance on the 10-9 (airport diagram) and taxied towards Taxiway B. The Company 10-9 page erroneously depicts Taxiway B as a STRAIGHT taxiway delineating the edge of the ramp. In actuality; the ramp has a rectangular cutout area that extends past Taxiway B. Upon approaching the edge of the ramp; we turned to join what we thought was Taxiway B but found ourselves turning into the end of the cutout and onto the snow-covered; grassy area at the edge of the ramp. The aircraft came to a gentle stop. Upon realizing we had departed the ramp area; we contacted MKE Operations and Maintenance Personnel. The aircraft gear pins were inserted. After conferring with Company Ground Operations; Maintenance Control; Dispatch; and MKE Airport Operations; it became clear that the best course of action would be to deplane the Passengers before attempting to reposition the aircraft. We briefed the Cabin Crew and Passengers in-person from the cabin.To ensure a safe deplaning on an otherwise slippery; ice-covered ramp; gravel/sand was placed on the ramp along the aft footprint of the aircraft. Flight Attendants provided a water service to the Passengers while we awaited the arrival of the 'TSA-cleared' buses. The Passengers were deplaned by the Flight Attendants in a very orderly fashion; three rows at a time; from the aft entry door via airstairs and taken via buses to the terminal. The checked bags were unloaded. The aircraft was defueled; repositioned to a terminal gate; and placed back into service. No injuries or aircraft damage were reported during the event.MKE Airport Operations informed us that plans were in the works to mark off the ramp area in question with 'xxx' markings and place lights to better delineate the irregular taxiway boundary. An update to the MKE 10-9 chart would help provide better situational awareness during taxi operations particularly during periods of inclement weather and/or in the presence of ground clutter.
Second reporter narrative
We pushed off Gate XX in MKE at approximately XB:00 AM. We decided to taxi out on one engine because of a longer taxi to Runway 1L and the need to deice. Due to the Runway 1L departure; we expected to use the South Deice Pad. We were given taxi instructions to the West Deice Pad. We discussed the routing and began to taxi. Due to the angle of the pushback; Taxiway B to join V was farther behind us than we realized. As we made the left turn from the gate area; I set up the number 2 radio with the West Deice Pad frequencies; instead of the South Deice Pad I had preloaded at the gate. I should have waited until we had joined the taxiway adjacent to the ramp; so that both of us ensured compliance with taxi instructions. When I looked up from the radio; I knew the aircraft was in the wrong place. Due to the position of the airplane; and the direction we were facing; I suggested an immediate right-hand turn in the direction of the terminal.At that time; Ground pointed out Taxiway B was to the left. With only the #2 running; Ground's input; and my inability to see out the CA (Captain) window; I had no reason to question the decision to turn left. Moments later; the nose wheel departed the pavement. We stopped and coordinated with ATC and Operations. The Passengers and luggage were deplaned and re-accommodated.Limited ramp lighting; taxi lines and marking obscured by reflections on the moisture from the previous evening's snowfall; and the 10-9 not reflecting the actual layout of the pavement contributed to the event. The light covering of snow also obscured the pavement edge. A MKE County Operations Employee indicated that they will be adding markings to the pavement that is not illustrated on the 10-9. The taxi diagram gives the impression that the pavement is continuous and even; when in reality there are cutouts between the fuel farm and Taxiway V; where the nose wheel departed the pavement.I should have maintained situational awareness by delaying changing radio frequencies until we were established on the correct taxiway. Adding the fuel farm and additional pavement; even if it is not intended for aircraft use; to the 10-9 will help enhance situational awareness. When I first recognized we weren't where we should have been; we should have stopped and sorted things out before moving again.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.