Here at Luke, they use burner when they’re in air to ground config, (2 tanks, 2 TERs, bombs etc.), and don’t when they’re in air to air config, ( Centerline tank, 120s and 9s.). Sometimes you can see the burner and sometimes you can’t. On sunny days you can’t really see it, all you get is the heat blur, whereas on overcast days, and obviously dawn / dusk you can see it very well. Like Panther and MV said, us maintainers can tell just by looking, and you can tell it’s in burner just by hearing it too as it goes by. You can “feel” it! It’s awesome!!!