The Situation is so embellished that it contains elements of scenes later in your hierarchy. Rewrite the description of this item. You are focusing on a scene too long for the intensity of anxiety it has the power to produce. Decrease the amount of time imagining the scene. Rewrite the item to break it into two new items.
Some people call it a graduation flight.
You might feel comfortable doing this on your own, or you might want a psychologist to accompany you, either on a commercial airline or on a small charter aircraft. Either way, remember that once you make one flight, the next flights become easier. Before each flight, you should work through your anxiety hierarchy to reinforce your ability to remain relaxed. Above all, remember to practice your relaxation technique on a daily basis, so you can both cope with daily stress and also improvise short desensitization sessions as needed. Psychotherapy by reciprocal inhibition.