You won't see a specific place to enter aircraft mileage as a business expense, either on a Form 1040, Schedule C (self-employment), or a business entity tax return, such as Form 1120, 1120S, or 1065.
Business mileage, per the IRS, is really for wheeled ground transportation -- think of cars and trucks. For your aircraft, you'll need to enter the actual expenses of operation. There is no standard business mileage rate for air travel as far as it pertains to personal aircraft operation.
Where you record the actual aircraft operating expenses (crew, fuel, maintenance, insurance, airport fees, etc.) is somewhat left up to your discretion. One suggestion, after totaling up your expense receipts, is to report this on a business expense line for "other." You can then name your own category. (Please see the screen capture images attached to this answer for a visual aid.)
TurboTax has a place near the end of the business interview where you'll have the opportunity to input these "other" expenses.
Thanks for asking this important question and safe flying!
