In order to cope with the increasing demand of communication capacity in the aeronautical sector, the Future Communications Infrastructure has been developed. For air ground communications currently two candidates are considered for the L-band digital aeronautical communication system. Both L-band systems use frequency bands assigned to both civil and military navigation systems. Hereby of special interest is the distance measurement equipment due to its wide and extensive use in the civil aviation. Prior to the deployment of any of the candidates, the compatibility towards those legacy systems has to be confirmed. This paper presents the result obtained during compatibility measurements of LDACS1 carried out at labs of the German air navigation service provider in March and August, 2011. Both results for interference on the DME caused by LDACS1 and vice versa are dealt with.