How to up the score?

This is my second question on this project. I am almost completely finished but I would like to know how I can implement a score into my world. I have it split between two 3d text's. ("Score:" and "0"). What would I use to make it to where for every second the player doesnt crash, the score goes up? (My game is kinda like a flight simulator? just has a plane flying)

Thanks
-Zack