This first happens in mission The Arbiter. It should be unmissable if you're playing solo. (It's possible to miss this in co-op) About a third of way through the mission. The Heretic leader will run away and jump into a yellow banshee. Follow him, and hop into another yellow banshee. The achievement should pop immediately.
If it doesn't, the next area has a bunch more yellow banshees. You could also unlock this achievement in the next mission, with another yellow banshee.
Note: It is possible that this method of unlocking the achievement might be unintentional. Let me know if the solution stops working. Certain skulls might disable this achievement.