If you are running late and flying a simple route, FMS1 requires less programming and has less potential for subtle imbedded bugs to cause problems. If you are flying a more complex route where ETP, nearest airport, multiple directs, etc are of more importance, the FMS2 is more capable. To complicate matters, some of our aircraft have a hybrid version (FMS 1 1/2?) that incorporates most of the benefits of FMS2 with the simplicity of FMS1. Of course it is only 4 airframes and no longer supported! Cheers Cropduster.