Definition
In instrument flying, to set the aircraft on a specified flight condition — such as a heading, altitude, course, airspeed, or rate of climb or descent — and hold it steady within tolerances, with the appropriate instrument indications confirmed and stable.
Plain English
To get the airplane onto the exact flight path or flight condition you've been told to fly, and keep it there steady enough that the instruments confirm you're holding it.
Context Anchor
Used in attitude instrument flying when setting a new attitude, heading, climb, descent, or other controlled condition by reference to the flight display.
Derivation
From the Latin stabilire, meaning 'to make stable or firm.' In aviation it carries that same idea — not just reaching a condition, but settling into it so it holds.
Why Pilots Care
Many IFR procedures and ATC instructions only take effect once the aircraft is established. For example, certain altitudes can only be descended to once established on a published segment of an approach. Reporting 'established' too early — before the aircraft is actually steady on course — can lead to altitude busts or terrain conflicts.
Intuition Check
Do not read establish as merely “start.” In this context, it means set the airplane into the desired condition and make sure it is steady there.
Example Sentence 1
Once established on the inbound course, the pilot began the descent to the next altitude.
Example Sentence 2
After intercepting the localizer, establish the aircraft on the approach course with wings level and proper descent rate.