The route is not transmitted from the aircraft. We are receiving the call sign of the flight from the aircraft and comparing it with large databases of airline and airport schedules to find the matching flight number.
Once the call sign is matched to a flight number, we are able to show the route of the flight. Routes may be missing if an airline has not submitted a flight schedule or we have failed to make a match for some reason, for example, due to an incorrect call sign or a severely delayed flight.
Many deliveries, positioning and charter flights may be missing route information as this data is often missing in the databases that we use.
We are working continuously to acquire as much route data as possible.