Neat problem to work on. The tail number lookup is the hard part and it sounds like you solved it the right way, by finding the people who actually track this obsessively rather than trying to scrape it yourself.

Two questions: how stale does the tail assignment data get in practice, and do you have a way to detect when an enthusiast spreadsheet goes unmaintained? And what happens to your probability estimate when an airline swaps aircraft last minute, which seems to happen pretty often on regional routes?