Allegiant Travel Company is on the hunt for a dozen used A320s to economically feed its transition to a single fleet type and jump-start capacity growth. The ultra-low-cost carrier plans to end 2017 with 89 aircraft, including 37 McDonnell-Douglas MD-80s. It will retire the venerable twinjets in 2018 while adding 30 Airbus aircraft, leading to a net drop of seven aircraft in its fleet. By the of 2020, however, plans call for the airline to be operating 110 aircraft, including 37 A319s. The ...