Depending on the circumstances of the event, time lapse since the event and the persons subsequent feelings toward themselves after the event, it is possible that anything ranging from outright grief to Post Traumatic Stress Disorder / Syndrome could have something to do with your friends apparent behaviour.
Grief is a time process whereby a person will go through different recognisable phases. An interruption to any of these phases can result in the lengthening of the grieving period. A sudden change in lifestyle, a traumatic event, separation, or the ending of something like a job a person just loves doing may trigger a grief response. It depends alot on the person.
PTSD can be the result of a single event or a series of events, that may have been beyond the persons ability to deal with them in a percieved normal fashion. It is usually quite manageable depending on severity, the cause and the stability of the patient themselves. It is very possible to return to normality but it takes time. Occasionally lots of it, especially around event anniversary times.
Without getting into details, I went from not being able to remember very basic stuff like starting a car to full recovery after a particularly nasty event. I had help along the way from a recommended professional psycologist, my family and later when I could face them again, my friends. The first six months were hell, as alot of life then was purely reactive, not proactive and I wasnt acting my logical self, even though I could reason logically.... then Id kick myself for being over reactive, and silly. (like the complusive checking door locks, windows and curtains repeatedly even though I knew everything was okay). This behaviour resulted in severe self doubting about my ability to conduct life in a normal fashion. That is going to work happy, flying, interacting comfortably, coming home, socialising etc.
It is not a death knoll on a career but can stretch the timing out a bit.
The symptoms as you describe them, (flying had nothing to do with his loss of confidence in machinery), its more possibly a feeling of being not totally in control after a nasty time resulting in triggering the grief process or at worst, PTSD.
Your willingness to help is primarily a supportive role, in the fact that I wonder if his self confidence appears to have been shattered. Life goes on as normal around the person, and feeling alone or different from others, even amonst close friends can be an issue. Tiredness resulting from lack of sleep, mood swings and so on. Support and normality, and slow bites back into life are the usual tact.