(Reuters) -Australia's flag carrier Qantas Airways Ltd on Thursday posted a 12.8% fall in first-half profit and announced an additional on-market stock buyback of up to A$400 million. That marginally missed a consensus estimate of A$1.26 billion, according to Jefferies. Henry Jennings, a senior analyst at Marcustoday Financial Newsletter, said it is a positive to do another buyback, especially given the capital requirements of the company but does put some support under the stock.