Standard Instrument Departure / Standard Terminal Arrival Route

What are SID/STAR?

Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) are pre-published procedures that define the path an aircraft follows when leaving or approaching an airport. A SID specifies the route from the runway to the en-route airway structure, including waypoints, altitude restrictions, and speed constraints. A STAR does the reverse, guiding aircraft from the en-route phase through the terminal area to a point where they can begin an instrument approach.

These procedures serve multiple purposes. They separate departing and arriving traffic from each other, provide noise abatement routing over less populated areas, ensure terrain clearance in mountainous regions, and sequence traffic flows to maximize airport capacity. At busy airports, dozens of SIDs and STARs may be published, each serving different runway configurations, traffic directions, and operational conditions. London Heathrow, for example, publishes over 50 SIDs and STARs to manage its complex traffic flows.

Modern SIDs and STARs are increasingly designed as RNAV procedures, defined by GPS waypoints rather than ground-based navigation aids. RNAV SIDs/STARs enable more precise, repeatable flight paths with tighter spacing between routes, which increases airspace capacity. Many airports have replaced their conventional SIDs and STARs entirely with RNAV versions, while others maintain both conventional (ground-based) and RNAV (GPS-based) variants as backup.

Why It Matters for Airspace Risk

When SIDs and STARs are designed exclusively around RNAV/GNSS waypoints, GPS interference can render them unflyable. If an aircraft cannot navigate to the waypoints on an RNAV SID, ATC must provide radar vectors — manual turn-by-turn instructions from the controller. This works at well-staffed radar-equipped airports but dramatically reduces capacity, as controllers can only handle a fraction of the traffic compared to self-navigating RNAV procedures. At airports without radar, the loss of RNAV SIDs/STARs can effectively halt instrument operations.

Airports that have maintained conventional SIDs and STARs alongside RNAV versions have built-in resilience. When GPS is denied, traffic can revert to conventional procedures using VOR and DME. This comes at a cost — conventional procedures are less efficient and support lower traffic volumes — but they keep the airport operational. For airspace risk purposes, knowing whether an airport has GPS-independent departure and arrival procedures directly determines its vulnerability to GNSS interference. Airports in GPS-contested regions that rely solely on RNAV SIDs/STARs represent a higher risk category for operational disruption.

Key Facts

• •SIDs define the departure path from runway to airway; STARs define the arrival path from airway to approach.
• •Modern RNAV SIDs/STARs are defined by GPS waypoints, enabling precision routing but creating GPS dependency.
• •Major airports publish 30-50+ SIDs and STARs covering different runway configurations and traffic flows.
• •GPS denial forces reversion to radar vectors, reducing airport capacity by 30-50% at facilities without conventional procedures.
• •Continuous Descent Approaches (CDAs) embedded in modern STARs reduce fuel burn and noise but require precise navigation.

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