The FIDS API is specifically designed to provide the data needed by FIDS (Flight Information Display System) displays such as those commonly deployed in airport terminals, hotel lobbies, and other places travelers are found.
It uses a weighted algorithm and is not designed to retrieve all flights. Rather, it is designed to show a reasonable number of the most relevant flights and the results can be affected by the time of day, number of scheduled flights, current airport delays, and other specified filtering. The FIDS API has the notion of an arbitrarily specified rolling time window. It also will carry over delayed flights that are now estimated to depart in the specified time window.