We analyze the coexistence between the L-band Digital Aeronautical Communication System¿option 2 (L-DACS2), which is a preselected candidate to support future continental communications, and the distance measuring equipment (DME), which is an L-band radionavigation system in use for decades, now implemented in all aircrafts. We focus on the impact of L-DACS2 interference on the DME performance under the cosite scenario, where both equipment are located in the same aircraft. After a brief presentation of both systems, we study this critical scenario (from the system coexistence viewpoint), by proposing a new approach (different from classical frequency-domain analysis) that takes into account system dynamics and their technology characteristics. Based on various implementation methodologies, we show in the last part of the paper, the effect of some parameters on the coexistence between the on-board L-DACS2 transmitter and the on-board DME receiver.