You could do this a number of ways, including going really basic and just using a bool that ticks true once the plane has collided once and is checked on each collision. If it’s true when you hit something, it would have to have already hit something once and will trigger the explosion.
You could also do something along the lines of incrementing an Int each time it hits something to give you more flexibility with multiple states possible in addition to your “Fresh, Burning, Exploding” ones.