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50 ft OBS — Aviation Definition | Keynomen Aviation

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50 ft OBS

OBS is the abbreviation for obstacle.

Plain English Meaning

An imaginary 50-foot-tall obstacle the chart pretends is sitting at the end of the runway. The takeoff distance shown is how far it takes the airplane to get off the ground and climb up over that 50-foot mark.

Full Definition

A standard 50-foot obstacle used as the reference height for measuring takeoff distance in aircraft performance charts. Takeoff distance is calculated from the start of the takeoff roll to the point where the aircraft has climbed to 50 feet above the runway surface, simulating clearance over a typical obstacle at the end of the runway.

50 ft OBS

Context Anchor

Seen as a label or column in takeoff distance charts when checking whether a runway is long enough for the planned takeoff.

Derivation

Obstacle comes from a Latin idea meaning “to stand in the way.” That fits the aviation use: it is something in the takeoff path that the airplane must climb over. ft is simply the shortened form of feet.

Why Pilots Care

It tells the pilot whether the runway is long enough to clear obstacles at the departure end under given conditions.

Grounding Statement

The key point is that 50 ft OBS includes both getting airborne and climbing high enough to clear a 50-foot object.

Intuition Check

Do not read 50 ft OBS as just the ground roll. It means the total distance needed to take off and clear a 50-foot obstacle.

Example Sentence 1

The chart showed a takeoff distance of 1,400 feet to clear the 50 ft OBS at our weight and density altitude.

Example Sentence 2

Higher temperature increased the 50 ft OBS distance shown for this aircraft.