three-eight-hotel wrote:

snip
I would do it whether there was a tax advantage or not, but it would be
great knowing that it is a completely legitimate write-off.

I calculated the actual costs for the flight (fuel, oil, used for flight's
duration), then included those expenses in my charitable contributions for
the year. I also noted in my logbook that the flight was a charity flight
and included the organization name in the comments section.

The organization then sent me the required letter after the auction
completed that stated no goods or services were received in exchange for my
donation.

You obviously need to clear this with your tax accountant, but IME, as long
as the charity is recognized by the IRS (US tax collector), I am eligible
to write off the donated flight.

--
Peter