Perusing Flightaware today and found a wacky flight number for SY
The destination is Escanaba MI. Now I am pretty sure SY didn't get a slot for service to Escanaba. They do have service to MSP via LAN. Given the flight number, I assume that it is a charter of some type.
This begs the question, what are the rules for charters into DCA? Given the slot restrictions and security considerations, I can't imagine just any Tom,, Dick, or Harry (or Tanya, Debbie, or Hannah for that matter) with an airplane can land at DCA. Who decides what charters are allowed?