The thesis describes the algorithms design required to perform in-trail self-spacing during continuous descent approaches. Both distance-based and time-based spacing is treated. The CDA-procedure that is investigated is the Three-Degree Decelerating Approach (TDDA). The results of various off-line and simulator experiments as well as test flight data are presented and discussed. Both distance-based and time-based self-spacing are proven to be feasible solutions to the problem of introducing CDAs while maintaining realistic runway throughput numbers.