Definition
A preplanned instrument flight rules (IFR) procedure published for pilot use, in graphic or textual form, that provides obstruction clearance from the terminal area to the appropriate en route structure. There are two types: Obstacle Departure Procedures (ODPs), which are designed solely to provide obstacle clearance, and Standard Instrument Departures (SIDs), which are typically designed to provide a transition from the airport to the en route structure and may also include ATC requirements such as climb gradients, communication points, and crossing restrictions.
Plain English
A published, ready-made route for leaving an airport in the clouds or low visibility, designed to keep you safely above terrain and obstacles until you join your en route course. Some are built only to keep you clear of obstacles; others also help organize traffic flow and tell you what altitudes and headings to fly.
Context Anchor
A pilot encounters this during instrument flight planning, in an instrument clearance, or on a published departure chart for an airport.
Derivation
"Departure" comes from the Old French departir, meaning "to divide" or "to go away." In aviation, the word focuses the procedure on the leaving phase of flight -- specifically, the climb-out from the airport to the en route structure.
Why Pilots Care
Following the procedure ensures required obstacle clearance during instrument departures from airports where terrain or traffic complexity makes a standard climb unsafe.
Intuition Check
Do not read this as simply “a departure where the pilot looks at instruments.” It is a specific planned procedure for leaving an airport under instrument flight rules, and it may matter even when the weather looks good.
Example Sentence 1
Before takeoff, the pilot reviewed the Instrument Departure Procedure to confirm the required climb gradient and initial heading.
Example Sentence 2
ATC assigned the Instrument Departure Procedure to keep the aircraft above terrain during the initial climb in low visibility.