Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Flight Crew Last 90 Days 40; Flight Crew Total 6000; Flight Crew Type 4000
Situational Awareness
Ground Excursion Taxiway
Flight Crew Requested ATC Assistance / Clarification
Airport; Human Factors; Aircraft
After normal preflight and engine start operations we received a taxi clearance. Paraphrasing; taxi to RWY 25L via Taxiway A; A13; hold short of RWY 25L. It was the taxi clearance we expected and briefed. As we started the taxi we commenced with the taxi checklist. The taxi checklist was completed. As we approached the 90 degree turn from Taxiway A onto Taxiway A13 we discussed the narrow taxiway and the tight 90 degree turn. During the turn; even though we favored the left side of the taxiway; the right main wheel went off the taxiway. We contacted ground control for assistance.  Suggest an Airport Operations  review of the DVT intersection of Taxiway A and A13.  Convergence of two narrow taxiways.  The inside of the turn is not a smooth arc for transition from Taxiway A to A13. The old   taxiway had a smooth arc inside of the turn.  The taxiway markings are at the very edge of the taxiway with no hard surface margins. The old   taxiway had hard surface outside of the taxiway markings creating a margin.For narrow taxiways the crew should use the onboard cameras for situational awareness for wheel/edge proximity.
G450 First Officer experiences a taxiway excursion at DVT during a turn from Taxiway A to A13. The right main gear departs the paved surface during the turn.