Although uncommon and quite strong for this purpose, as a last resort can haloperidol theoretically be be used for plane anxiety?

Use rails or highway: A person with severe plane anxiety can travel by train (amtrak even has sleeper cars on their nicer trains), take a bus, or drive himself. Overseas travel can be done partly by cruise ship, if he absolutely won't take to the air.

Haloperidol : Theoretically, haloperidol can be used for phobias like fear of flying. However, i've never used it for this as the side effects can be severe. I recommend that you talk to your doctor about all the alternatives for flying phobia. You might also consider counseling or cognitive-behavioral therapy to help you overcome your phobia permanently.

Not Haldol (haloperidol): If you're going to treat this kind of anxiety medically, a benzodiazepine like valium makes more sense than haloperidol.