professional armchair pilot
A professional armchair pilot is a person who is obsessed with aviation and aircraft, but has no actual pilot training or experience. They may spend hours studying flight manuals, watching aviation videos, and discussing the finer points of aircraft performance, yet they have never even set foot in the cockpit of an actual plane. Despite their lack of practical knowledge, these individuals may still consider themselves experts on all things aviation and may even offer their unsolicited opinions on piloting techniques and aircraft design.
"I asked John for his advice on flying my small aircraft, but it turns out he's just a professional armchair pilot who's never even been in a cockpit. I think I'll go with the advice of the actual pilot I know."