Definition
A flight condition in a multi-engine aircraft in which one engine has failed or has been intentionally shut down, leaving the remaining engine or engines to provide all thrust. OEI performance data, procedures, and obstacle clearance requirements describe how the aircraft must be operated and what climb performance it must achieve when this condition exists, particularly during takeoff and the initial climb.
Plain English
OEI means one of the airplane's engines is not running. The pilot has to fly, climb, and clear obstacles using only the engine or engines still working.
Context Anchor
Seen in multiengine takeoff planning, climb performance, and obstacle-clearance requirements after takeoff.
Why Pilots Care
Determines whether the aircraft can safely climb and clear obstacles if an engine fails at the most critical point during takeoff.
Intuition Check
OEI does not always mean the engine has physically stopped turning. In performance planning, it means one engine is not providing usable help, so the aircraft must be treated as if that engine is unavailable.
Example Sentence 1
Before departing the short runway surrounded by terrain, the crew reviewed the OEI takeoff procedure and confirmed the aircraft could meet the required climb gradient with one engine inoperative.
Example Sentence 2
Pilots calculate OEI performance before every multi-engine takeoff to confirm obstacle clearance is still possible.