Definition
An obstruction is any natural or man-made object — such as a tower, building, tree, terrain feature, or construction crane — that rises into navigable airspace and may pose a hazard to aircraft, particularly during takeoff, approach, and low-altitude operations. The abbreviation OBST is used on charts, in NOTAMs, and in airport documentation to flag these hazards.
Plain English
Something tall enough to get in the way of an aircraft. OBST is just the short way of writing 'obstruction' on charts and in flight notices.
Context Anchor
Seen in aviation notices, airport information, and preflight briefings when something such as a crane, tower, vehicle, equipment, or terrain may affect aircraft movement.
Derivation
From the Latin 'obstruere', meaning 'to build against' or 'block up'. The aviation use keeps that core idea: something built or standing in the way of the path you want to fly.
Why Pilots Care
Unmarked or unknown obstructions create collision risk, especially during low-altitude operations, night flight, or instrument approaches.
Intuition Check
Do not read obstruction as only a full blockage. In aviation, an obstruction can be anything that creates a hazard or reduces safe clearance, even if the aircraft can still pass near it.
Example Sentence 1
The NOTAM listed a new OBST — a 280-foot crane — half a mile off the departure end of Runway 27.
Example Sentence 2
A NOTAM warned of a new OBST near the final approach course.