[ehaughee]

A couple ideas come to mind solving slightly different problems

1. Flight discovery

It would be interesting to propose a date and (optional) arrival time and location and have the service look up like the top 5 cheapest flights or something and link to a purchasing site (affiliate link kickbacks might be a viable way to generate revenue here but I have effectively zero context/experience here).

The rest of the user story/flow (aka what happens when someone chooses to purchase a flight from the list) is interesting here but simpler is probably better (e.g. just have them follow the flow in point 2 below) unless there's some simple way for Calenday to know which flight you bought and surface that to collaborators.

2. Flight coordination

It would be nice if the trip "vanguard" or leader could put in their flight details and have that shown with some rich information from some flight tracker API. Might be able to simplify the flight details input portion with some kind of flight tracker API (e.g. Airline, flight number, date and then it would pull the departure/boarding times, terminals, gates, or whatever is available).

Going a bit more democractic, and maybe what you were talking about with showing availability, if people buy different flights from one another (e.g. coming from diverse origins, or differing availabilities or price sensitivities), having an easy way to see when each collaborator/co-traveler will land in the given destination would be very useful/cool.