Drilling a stack made of fiber-reinforced plastic and metal layers is investigated and presented in this paper. Improvement of performance can be achieved if the process parameters will be adapted to the various drilled materials and drill position. Therefore, the true position of the drill should be precisely known. An algorithm for real time monitoring of drill position is suggested. Drill position is defined by analyzing acoustic emission signals from a sensor located near the drilling point. During drilling of CFRP and Al-stacks, it could be proved that material changeover can be identified ahead of time, especially when using stepped drills.