Definition
A preplanned instrument flight rules (IFR) departure procedure published in graphic and/or textual form, providing pilots with a structured route from the runway to the en route structure while ensuring obstacle clearance and orderly traffic flow. DPs include Standard Instrument Departures (SIDs) and Obstacle Departure Procedures (ODPs).
Plain English
A pre-published set of instructions for flying out of an airport under instrument rules. It tells the pilot exactly what headings, altitudes, and routes to follow after takeoff so the airplane stays clear of terrain and obstacles and fits into the air traffic system.
Context Anchor
Seen during IFR preflight planning, in departure clearances, and on instrument procedure charts for the airport you are leaving.
Derivation
From Latin 'instrumentum' (a tool) and 'departure' (from Old French 'departir', to divide or go away). 'Instrument' here points to flight by reference to cockpit instruments rather than by looking outside, which is the regime these procedures are designed for.
Why Pilots Care
Following the published DP guarantees obstacle clearance and a predictable path to join the enroute system when visibility is low.
Intuition Check
Do not read “procedure” as casual advice. In instrument flying, a DP is a published path or set of instructions that matters for obstacle clearance, and some DPs must be specifically assigned or cleared by air traffic control before you fly them.
Example Sentence 1
After receiving their IFR clearance, the crew briefed the DP, noting the initial heading, crossing altitude, and the fix where they would join the en route airway.
Example Sentence 2
During the instrument departure the controller confirmed the aircraft was on the assigned DP.