How eligibility is checked at the time of the flight
FlyerOS checks a booking against how the world will be when the flight happens, not how it is when you book.
Last reviewed
FlyerOS checks a booking against the state at the scheduled moment, not the moment you make it. A booking for three weeks' time is judged by how things will be then, not how they are today.
Why this matters
Say you book an aircraft today for the 14th, and that aircraft is due for a 100-hour check on the 12th at its current rate of flying. Checking "is it serviceable now?" would let the booking through, and it would strand a student at the aircraft on the day. FlyerOS instead asks "will it be serviceable on the 14th?", and blocks the booking now, while there is still time to move it.
The same applies to people. A rating that expires on the 10th does not stop a flight today, but it does stop a flight booked for the 11th, because on the 11th the rating will have lapsed.
Checked again at dispatch
The forward check when you book is not the last word. The world changes, a snag is raised, a medical lapses, a check comes due. So the booking is validated again at dispatch, against the state at that moment. Anything that has changed since it was booked is caught before the aircraft leaves.
What you see
When a future condition will fail, the reason names the date. "Expires 3 September, booking is 11 September" tells you the check is looking ahead to the 11th and finding the medical already expired by then. Fix the future cause and the booking clears.