I understand that the time frame by which all new a/c must be fitted with mode s is about september this year and all older aircraft will have to be retrofitted by Sept 05. Also Enhanced mode S is on the way and will be implemented late 05. Enhanced will transmit more data for example not just heading but also pre selected heading and preselected (armed) alt. Then there is ADS-B. of which I know nothing. Anyone care to enlighten?