This is analogous to the automobile expenses in IRS publication 526
Car expenses. You can deduct unreimbursed out-of-pocket expenses, such as the cost of gas and oil, that are directly related to the use of your car in giving services to a charitable organization. You cannot deduct general repair and maintenance expenses, depreciation, registration fees, or the costs of tires or insurance.
If you do not want to deduct your actual expenses, you can use a standard mileage rate of 14 cents a mile to figure your contribution.
You can deduct parking fees and tolls, whether you use your actual expenses or the standard mileage rate.
You must keep reliable written records of your car expenses. For more information, see Car expenses under Records To Keep, later.
Where the government allows something like $0.50/mile for business use of a vehicle, they only allow $0.14 for charitable contributions. They pretty much allow only direct out of pocket expenses. In the case of your own aircraft, the only direct out of pocket expenses are fuel and oil, landing fees, parking fees, etc, that are directly related to the flight made.
In the case of a rented aircraft, the entire rental charge is directly attributable to the flight, and is probably deductible.