A drilling rig assembly having a longitudinal axis and comprising a drilling rig skid and a derrick assembly having a derrick assembly pivot axis and being adapted to move relative to the drilling rig skid. The derrick assembly comprises a pair of derrick masts disposed on opposite sides of the longitudinal axis and comprising a rack, and a carriage assembly being substantially disposed between the pair of derrick masts, being adapted to move along the pair of derrick masts and comprising a pinion. The drilling rig assembly also comprises a means for moving the derrick assembly relative to the drilling rig skid, a pipe loader assembly having a pipe loader assembly pivot axis, and a means for moving the pipe loader assembly relative to the drilling rig skid. The derrick assembly pivot axis and the pipe loader assembly pivot axis are co-axial.