What makes an itinerary invalid is if it meets one of three conditions:
- It has overlapping flights in terms of times (i.e. two flights that are to be in the air at the same time.)
- Arrival and departure airports are not the same AND the departure airport is repeated within 12 hours.
- The flight number, departure and arrival information does not match a published schedule in our system.
This condition seems complicated, but its purpose is to identify when you're making the same point A to point B trip twice even if you are going via point C (e.g. PDX to LAS, then PDX to SEA and SEA to LAS) without invalidating co-terminal connections (it is perfectly valid to fly into LGA and out of JFK) or short business trips (e.g. SEA to PDX to LAX then LAX to PDX to SEA a few hours later.)