After take-off in instrument conditions, a pilot cannot simply turn toward the destination. Terrain, noise-sensitive areas and other traffic all have to be considered. A Standard Instrument Departure (SID) solves this with a published route from the runway to the en-route structure, the same for every aircraft that flies it.
Why SIDs exist
- They guarantee obstacle clearance during the climb.
- They keep departures separated from arrivals and other airports' traffic.
- They cut radio workload: ATC can say "cleared via the SID" instead of reading out every turn and altitude.
How SIDs are named
A SID is usually named after the waypoint where it ends, followed by a number and often a letter, for example WAYPOINT 1A. The number is the revision; it changes whenever the procedure is amended. The letter distinguishes versions, for example for different runways.
Watch: a SID chart breakdown
What is on the chart
- Runway and initial climb: the departure runway(s) the SID applies to and the first instruction, for example "climb on runway heading to 1,500 ft, then turn right".
- Route: tracks, radials or RNAV legs between waypoints.
- Altitude constraints: shown as "at or above", "at or below" or "at" a given altitude at specific points.
- Speed limits: maximum speeds for turns or segments.
- Initial altitude: the level to stop climbing at until ATC clears higher.
- Transition altitude: where pilots change to the standard setting of 1013.25 hPa.
- Frequencies and notes: departure frequency, noise abatement rules, minimum climb gradients.
Conventional vs RNAV SIDs
Conventional SIDs are built on VORs, NDBs and DME. RNAV SIDs use waypoints flown by the flight management system, which allows more flexible and efficient routes. Many airports in India now publish RNAV SIDs alongside or instead of conventional ones.
How pilots use a SID
- Check the expected SID during flight planning and load it into the FMS.
- Brief it before departure: turns, constraints, initial altitude, what to do if an engine fails.
- Confirm the SID in the ATC clearance and read it back exactly.
- Fly it as published unless ATC gives radar vectors or a direct routing.
Exam summary
- SID = published IFR departure route from runway to en-route structure.
- Name = end waypoint + revision number + version letter.
- Altitude constraints: at or above, at or below, at.
- Initial altitude: do not climb above without clearance.
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