Hi guys,
when you are already airborne and your FMS crashes I would accept you continueing and not only at low level but at normal crusing level. But if you are on ground I would say go back to the gate and get it fixed.
In Zürich (according our book) we accept non RNAV aircraft over the alpine area up to FL160 (not sure if CFMU will accept as well).
@Denti: please confirm you were airborne and ATC Zürich told you you are not accepted as long you have no RNAV?!?
greetz
Johannes