Depreciation is loss in book value.
You will not lost directly your net cash income, because your airplane is loosing on it's book value. You will deprive your virtual amount of money in your books, and add then this virtual value to your expenses, which is artificially expense increase to pay lesser taxes. Nowhere is real money.
Book value =/= Cash income
And currently this heavily impacts the cash income.
It's not calculated in the operational cash flow though, that's why the cash flow graph is usually more than your income graph. For example, last week my airline made $7 mil in profit, that's including depreciation, however, my actually cash flow into my balance was $14 mil, because depreciation isn't calculated into your balance.