The six-seat, single-engine plane registered to Jeremiah 29:11 Inc, crashed under unknown circumstances killing all five passengers and the pilot.
Mr Valentine founded the company with his wife, which lists on its website the services provided including "pro bono flights for cancer patients, wounded veterans, boy scouts, and other individual and non-profit organizations".
The Independence Rural Fire Department said in a Facebook post that firefighter Nicholas Warner was also killed in the crash, along with two of his sons and his father, Bill Warner.
The Oklahoma Highway Patrol told News 9 that the group flew to Ponca City for breakfast and then crashed around 10:45am in a soybean field before it caught on fire.
Independence Community College head football coach Jason Brown paid tribute to his "friend" Mr Valentine.
Pirate Nation was devastated today with the sudden death of my friend and even better man, deepest condolences to his wife and kids our hearts hurt but he gave our program a great quote which we will never forget "success is not an accident" Fly forever
— Coach Brown (@INDYHEADCOACH1) August 5, 2018
RIP Tim Valentine pic.twitter.com/sSvEvdrTbU
He tweeted: "Pirate Nation was devastated today with the sudden death of my friend and even better man, deepest condolences to his wife and kids our hearts hurt but he gave our program a great quote which we will never forget 'success is not an accident'.
"Fly forever RIP Tim Valentine."
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