AFAIK applying for more than one 'trade' is kinda like applying to a few different companies... One really has nothing to do with the other. I don't think the AEC selection people are too interested in your/our application for pilot, shouldn't affect their selection process... Unless of course Pilot phones first and you accept? Then I would guess that your file would show as "unavailable" if the AEC group went to select you. I've never heard of someone getting a job offer for two different trades a couple weeks apart...
My guess is if you get an offer for a trade and decline, other trade applications should be completely unaffected. I was also told when selecting trades to apply for, YOU may look at your choices as #1, #2 and #3, but they see it as you've applied to 3 different jobs, each with completely separate criteria and selection systems... May as well be different employers! If so fortunate as to be wanted by many, just a matter of who calls first?
Read on other threads that Vocational Transfer from one trade to another isn't easy, or quick. If you got your heart set on Pilot, then by all means let that process play out first, declining others. IF for some reason it don't work out, can always call Recruiter to see if they can re-open your file or just reapply totally for other choice(s).