If I were you I'd try to use my cross domain knowledge (a pilot!) to position myself in a niche where there are few competitors, I have a hard time imagining there would be a lot of people that can call themselves programmer/pilot (though on HN for sure we have a few). That seems to be your unique selling point, so try to get as much traction there by recycling your old skills for as much as they're worth. As for men…
Safety critical software is absolutely not the thing to get involved with (especially off the bat)... That and security critical software have mountains of approval to get through before they can be used. The FAA is notoriously old fashioned. Also, I'd personally hate to be responsible for some crash because my flight planning assistance SaaS had a minor, off-by-one bug in it somewhere, or misinterpreted "thar be tor…
I've written code for the aviation industry (fuel estimation programs, one thing you really don't want to mess up with) so I fully understand the ins and outs of that, but a pilots log book has already been mentioned and that would be a nice thing to start out with.