There are a number of reasons why someone may end up with a fear of flying (aka aerophobia). For example, difficulties in one’s personal or professional life or merely a sense of worry or dread about events in the world (such as economic or political crises, or even crime or natural disasters, as communicated via mass media).
Someone with this elevated level of generalised anxiety is in a state of heightened susceptibility to negative impressions, and if required to fly, any incident during the flight which could remotely lend itself to negative interpretation will be seized upon, with the person imagining that something bad is happening.
This negative interpretation in turns generates more immediate anxiety, reinforcing the notion that something bad is happening, and leading to an obsessive attention with everything that he or she observes on the flight and the sense that an accident is imminent.
After the flight is over, between those negative associations and the related anxiety, a retroactive feedback loop can form in which all it takes is a memory, idea, or touch of nerves to provoke a reaction unpleasant enough to make flying something the sufferer would want to avoid forever after.
So the phobia is not so much the result of what actually happens to an aerophobia sufferer inflight as to what goes through his or her mind in these circumstances. At the end of the day, what generates fear and anxiety is like the proverbial mountain from a molehill – taking a perhaps insignificant incident observed on a flight and transforming it into a catastrophic threat. One always needs to keep this in mind!