I thought that TAA did the smart thing in keeping the DC9 in service until the B737-300 became available. Ansett (ie Abeles) bought the B737-200 as an interim aircraft until the B737-300 arrived. This was a very expensive process and the resale value of the -200s was significantly reduced once the high bypass turbo-fan equipped -300s started coming off the production line. TAA only had to introduce one type of aircraft and thus had lower "change over" costs. IMHO