What clues could i make for a surprise plane ride?

This Girl and i have been talking for two years, off and on, but things are getting pretty serious, I have planned a surprise single engine plane ride for the two of us. She is a missionary and loves to fly so i know she'll like it, she keeps asking me what the surprise is and i cant give her a clue because i literally do not have one... Any ideas? Also, do you think that if i asked her to be my girlfriend afterwards shed say yes?What clues could i make for a surprise plane ride?don't know a good clue- my bf said play freebird - but then again that can be taken very bad too - but do ask her steady i guess if you say it is getting more serious i take it you have hooked up- but ask her while in air for sure- when she gets that glazed lok in her eyes looking down on all- ask! this she will say yes if it is going as i think it is. have fun-