Definition
The airspeed an airplane should have reached as it climbs through 50 feet above the ground at the end of the takeoff run, used as a standard reference point for measuring takeoff and climb performance. It is the speed published in performance charts that allows the airplane to clear an assumed 50-foot obstacle at the departure end of the runway.
Plain English
The speed the airplane should be flying when it passes 50 feet above the ground after takeoff. Manufacturers use this height as a fixed checkpoint so pilots can compare their airplane's takeoff performance under different conditions.
Context Anchor
Seen in takeoff performance charts and takeoff technique discussions, especially when planning takeoff distance over an obstacle.
Derivation
The 50-foot height comes from FAA certification standards, which use it as a standard obstacle height for measuring takeoff distance. Choosing a fixed height lets every airplane's takeoff performance be measured the same way.
Why Pilots Care
It verifies that the airplane is meeting the published climb gradient needed to clear obstacles safely beyond the runway end.
Grounding Statement
Picture the airplane just clearing an imaginary 50-foot obstacle beyond the runway; the speed at that moment is the 50-foot barrier speed.
Intuition Check
Do not read “barrier” as necessarily meaning a physical fence, wall, or object. Here it usually means a standard 50-foot reference height used for takeoff planning.
Example Sentence 1
On a short-field takeoff, the pilot held the climb attitude until reaching the 50-foot barrier speed published in the performance chart.
Example Sentence 2
With the flaps set and the aircraft light, the 50-foot barrier speed was achieved well before the end of the runway.