I think it is widely accepted that the "Kyeema" accident in 1938 was the call to arms the Government could no longer ignore. However it followed two other high profile crashes, the ANA's Southern Cloud in 1931 and Airlines of Australia's Stinson in 1937.
The Government apparently already had plans for operational control centres at the capital city airports, but only Parafield, Archerfield and Mascot were completed before the war.