Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Taxiway
Air Traffic Control Issued New Clearance
Chart Or Publication; Human Factors; Procedure
DTW was in north flow. After pushback; we contacted Ramp Control for further instructions. We were told to taxi to Spot 5 and contact Ground Control. We taxied west to taxiway K; then south toward what we thought was Spot 5. After receiving taxi instructions to runway 4R; Ground Control notified us that we had taxied onto an active taxiway (K) without a clearance. We thought that the North Ramp consisted of the area leading up to the median separating taxiways K and Y.This event occurred due to lack of attention to detail. The chart for the North Ramp (10-9D) clearly shows that Spot 5 is located on 'Taxilane' E rather than Taxiway K. Furthermore; Gate notes; as well as text on the Company Departure page indicate the necessity to contact Ground Control prior to push back from those gates; as their proximity leads directly onto an active taxiway. We also noticed airport markings on the ramp area between the North Ramp and the movement area - these markings were difficult to notice from our starting location.I think that it would not be difficult for a crew that is unfamiliar with the DTW North Ramp to make a similar error in the future. An illustration on the North Ramp chart 10-9D of a line demarcating the North Ramp from the movement area would have helped to prevent this occurrence. Likewise; a cautionary note in the Company pages to supplement the current text would be helpful.
Departing DTW. After pushback was instructed by ramp control to 'taxi down to Spot 5 and contact ground...and spot 5 is abeam gate D-18.' Ramp control never specified to use taxiway(s) E or K. Spot 5 was not visible from pushback location. Taxied to the closest taxi line after push back which was taxiway K. Stopped abeam D-18 and contacted ground control. Received taxi instructions but was also advised we had taxied onto an active taxiway. Both taxi charts 10-9 & 10-9D DO NOT differentiate where the ramp ends; and where the active taxiway begins. In fact; upon taxi in after landing; ground control advised us to 'enter the ramp at XX'....while we were still taxing on taxiway Y. To us; this left the impression that both taxiway(s) E and K are under ramp control. A clear noted boundary between ramp and taxiway K are needed on both the 10-9 and 10-9D pages. Thank you for your attention to this matter.
Air carrier flight crew reported misunderstanding Ramp Control's taxi instructions and taxied on an active taxiway without clearance from Ground Control.