From Halopedia, the Halo wiki
Flyin' High is a medal in Halo 4, Halo 5: Guardians and Halo Infinite. In its first two appearances, it is earned by achieving a massive Mongoose or Warthog jump with a passenger and awards 5 points. In Halo Infinite it is awarded for achieving a massive jump in a fully-loaded vehicle, not just one passenger.
An easy way to obtain the "Flyin' High" medal is to drive a Mongoose with a passenger off one of the tower's launch pads in Ragnarok.