all these cost assessments are numbers on a spreadsheet. let's see what the numbers look like after 20 years on the line, with SrA mechanics and most flight hours by new Lt's and Captains. if they over-estimate the engine rebuild time, or if it really takes 2 hours instead of 30 minutes to remove and replace an avionics box (as was forecast), the calculation can veer in the other direction quickly. i predict the F35 will be the most expensive by flying hour of any (line) aircraft that has come before it.