Fair enough. I've seen enough bad UI choices in the mobile world that this made something itch between my ears is all, but it sounds like you've got a plan. Real world convenience is going to depend on the platform too, I suppose i.e. touchscreen vs mouse and keyboard. The Android app "Skydiving Logbook" has a decent solution with a pre-populated list of aircraft, DZs, jump types, etc. that a user is free to redefine or add to. It's either clunky or convenient, depending on the person, but could be one approach.
I just recently did something similar--but less intelligent on the data entry side--in a script for Google Spreadsheets (and Google Forms), so it'll be interesting to see where yours goes. Automatic email/calendar reminders for the customer are nice if you can figure out a good system for that.