Definition
The difference between the airplane's current airspeed and its stall speed in the existing configuration. A positive margin of speed means the airplane is flying fast enough that the wing is producing reliable lift and is not on the edge of stalling.
Plain English
How much faster you are flying than the speed at which the wing would stop producing enough lift to keep flying. The bigger the gap, the safer you are from a stall.
Context Anchor
Used when discussing liftoff, especially avoiding an early liftoff before the airplane has enough speed to climb safely.
Derivation
Margin' comes from the Latin 'margo,' meaning edge or border. Here it describes the cushion of speed you have above the dangerous edge — stall speed. The bigger the margin, the further you are from that edge.
Why Pilots Care
A sufficient margin prevents an aerodynamic stall or loss of control immediately after the wheels leave the ground.
Grounding Statement
At liftoff, the airplane should have enough speed not only to leave the ground, but to keep flying and begin climbing under control.
Intuition Check
Do not read “margin of speed” as just “going fast.” It means a safety cushion above the minimum speed needed to fly.
Example Sentence 1
The pilot held the airplane on the runway a few extra seconds to build a comfortable margin of speed before lifting off.
Example Sentence 2
A reduced margin of speed increases the risk of stall if the pilot over-rotates or encounters wind shear.