Definition
In aviation, objects on or near the ground — natural or man-made — that project high enough to interfere with the safe flight path of an aircraft, particularly during takeoff, climb, approach, and landing. Examples include trees, terrain, towers, buildings, antennas, power lines, and other aircraft.
Plain English
Things sticking up off the ground that an airplane needs to fly over or around safely — like trees at the end of a runway, a hill on the climb-out, or a radio tower near the approach path.
Context Anchor
Seen in takeoff planning, landing planning, airport diagrams, performance charts, and weight and balance discussions.
Derivation
From the Latin obstaculum, meaning 'something standing in the way' (ob- 'against' + stare 'to stand'). In aviation it keeps that literal sense — something standing in the path the aircraft needs to fly through.
Why Pilots Care
Excessive aircraft weight can reduce climb performance enough to strike obstacles, directly affecting takeoff weight limits and safety margins.
Grounding Statement
Picture taking off toward a line of trees at the end of the runway: those trees are obstacles because the airplane must be high enough to pass safely over them.
Intuition Check
Do not think of obstacles only as small objects sitting on the runway. In aviation, obstacles can also be tall structures, trees, rising ground, or anything near the flight path that the aircraft must avoid.
Example Sentence 1
On a hot day at maximum gross weight, the pilot calculated the takeoff distance carefully to make sure the aircraft would clear the obstacles at the end of the short runway.
Example Sentence 2
Weight and balance restrictions are set so the airplane maintains the climb gradient needed to avoid obstacles during departure.