Chapter 1$_{ }$ Departure Procedures  Introduction  Thousands of instrument flight rules (IFR) takeoffs and  departures occur daily in the National Airspace System  (NAS). In order to accommodate this volume of IFR traffic, air  traffic control (ATC) must rely on pilots to use charted airport  sketches and diagrams, as well as departure procedures  (DPs) that include both standard instrument departures  (SIDs) and obstacle departure procedures (ODPs). While  many charted (and uncharted) departures are based on  radar vectors, the bulk of IFR departures in the NAS require  pilots to navigate out of the terminal environment to the  en route phase. 