Complex sentence: Approval was given on 26 January 1973 for full-scale development of the AWACS system, with orders being placed for three pre-production aircraft to allow further development of the aircraft's systems, with the first of these aircraft flying in February 1975.
Split into simpler sentences: Approval was given on 26 January 1973 for full-scale development of the AWACS system. To allow further development of the aircraft's systems, orders were placed for three pre-production aircraft, the first of which performed its maiden flight in February 1975.