Where empty legs come from
When a jet flies a client one way, it often has to fly back or on to its next trip with no passengers. That repositioning flight is an empty leg.
Operators would rather sell it at a lower price than fly it empty.
The trade-offs
The route, date and time are fixed by the original trip. If that trip changes, the empty leg can move or disappear.
Empty legs work best when your plans are flexible.
How to catch one
Set a route alert and you will hear when a matching flight appears. They go quickly, so a short hold lets you confirm with the operator.
When to book a normal charter instead
If your date and time cannot move, book on demand. You choose the schedule and the aircraft waits for you.