To enhance the ability to compare across airlines, determine depreciation

expense for each $$100$ gross value of aircraft for each airline.

Do the choices the airlines make to account for depreciation matter? Are the

differences material?

How does the average age of each airline$$s fleet impact their depreciation expense?

What theoretical and practical reasons could be given to support the differences in depreciation method, residual values and useful lives used by the three airlines? Is different treatment proper? What does each airline gain or lose by doing so$?$ How do these relate to the companies$$ overall strategies?