I was told once in a human factors course that dehydration by as little as two percent has a measurable effect on a person's decision-making ability. The course was generally dull and redundant--I remember entertaining myself by devising and sharing "Buzzword Bingo" cards--but that factoid struck a chord. I don't have a reference to the study that determined that effect, but it's referred to here, and there's more advanced information on pilot dehydration here.
I carry a 750 mL water bottle with me in the cockpit, sometimes bringing an extra litre in the summer, so I never have to ration myself on water--but then I run up against the problem that not all the water my body processes is lost in sweat or water vapour in respiration. European researchers say that the need to urinate enhances the ability to make decisions but another study says the extreme need to urinate reduces cognition and working memory as much as a 0.05% blood alcohol level.
Flying requires decision making and working memory. I heard a pilot today advise ATC that they were landing "with one secured." If I decide to shut down one engine in flight and am thus landing with the power of only one, it would probably be a good decision to delay putting the gear down until I was sure I would not need to overshoot. But despite all the things I might be thinking during that approach, I would need the working memory to remember that I haven't extended the gear yet. And I'd really rather not be landing with my legs crossed.
There are a lot of resources available through Transport Canada and other aviation agencies around the world to help us pilots improve our ability to make safe decisions. We can get information on accidents others have suffered or avoided, information on weather, deicing, aerodynamics, communication, psychology, physiology and ... I don't have time to read it all. I like to think I have the general idea, however.
There's one thing I'm out of touch on, though. How can you call yourself a professional pilot and take people's life into your hands while impaired on recreational drugs? I'm disgusted. Yellowknife is not a big place, and Tindi hires through the ramp, so he wasn't new in town. There were undoubtedly people who knew what Matthew Bromley's job was, when he was flying and what he was smoking. They are irresponsible too.
I still think this anti pot-smoking poster is hilarious, but I want my fellow pilots to be responsible. Their behaviour reflects on me.