Definition
A runway whose approach, departure, and surrounding surfaces are clear of objects — such as trees, buildings, towers, terrain, or vehicles — that would penetrate the protected airspace required for safe takeoff, landing, and climb-out.
Plain English
A runway with nothing tall or solid in the way of taking off or landing. The path in and out of the runway is clear, so the aircraft has room to climb away or descend without anything to fly into.
Context Anchor
Pilots use this idea when deciding whether a runway is safe for takeoff, landing, or an emergency landing choice.
Derivation
“Obstruction” comes from a Latin word meaning “to block or build in the way.” “Free” means not blocked. In aviation, the phrase points to a runway that is not blocked by anything the aircraft could hit.
Why Pilots Care
Allows pilots to use standard performance charts and procedures without adding obstacle-avoidance margins, simplifying go/no-go decisions during training and operations.
Intuition Check
Do not assume obstruction-free means only that the painted runway surface looks empty. It also means there is nothing close enough to the aircraft’s takeoff or landing path to create a strike hazard.
Example Sentence 1
Given the short field and high density altitude, the instructor recommended choosing an obstruction-free runway for the student's first solo cross-country.
Example Sentence 2
During the lesson on runway selection, the instructor pointed out that the longer runway was obstruction-free, allowing a straight-out departure.