Aug 11 (Reuters) - Nav Canada NAVCA.UL
* Nav Canada - will proceed with its proposal to decrease existing base rates charged to its customers by an average of 3.5 per cent
* Nav Canada - will also implement a temporary one-year rate reduction of 0.4 per cent
* Nav Canada - company also announced its decision to reimburse its customers approximately $60 million in a one-time 4.6 per cent refund
* Nav Canada - 3.5 per cent average reduction to base rates and 0.4 per cent one-time rate reduction will both become effective on September 1, 2017