Definition
The lowest groundspeed at which a tire can begin dynamic hydroplaning on a wet runway. For a smooth, round tire, it is approximately 8.6 times the square root of the tire pressure in pounds per square inch (PSI). At or above this speed, standing water can lift the tire off the runway surface, causing loss of braking and steering effectiveness.
Plain English
The slowest speed at which your tires can start skimming on top of standing water instead of rolling on the runway. Below this speed the tires stay in contact with the pavement; at or above it, water can get under the tire and lift it.
Context Anchor
Seen in takeoff and landing performance discussions for runways with standing water, especially when judging braking and control after touchdown or during a rejected takeoff.
Derivation
‘Minimum’ here means the lowest speed at which the effect can occur, not a target or required speed. ‘Dynamic’ comes from the Greek dynamis (force, power) and refers to hydroplaning caused by the force of water building up under a moving tire. ‘Hydroplaning’ joins hydro- (water) with ‘plane’ in the sense of skimming or gliding across a surface.
Why Pilots Care
Above this speed braking and directional control are lost until speed drops or the runway dries.
Analogy
It is similar to a water ski: at low speed it sinks into the water, but at higher speed it rides on top. A tire can do a smaller version of that on a wet runway.
Grounding Statement
Picture a fast-moving tire meeting more water than it can squeeze out of the way, so the water lifts the tire and the runway grip fades.
Intuition Check
“Minimum” does not mean hydroplaning will always start exactly at that speed. It means this is the lowest estimated speed where dynamic hydroplaning can begin under the right wet-runway conditions.
Example Sentence 1
With main tires inflated to 49 PSI, the minimum dynamic hydroplaning speed is about 60 knots, so the pilot planned a longer landing roll on the wet runway.
Example Sentence 2
The pilot checked the minimum dynamic hydroplaning speed before landing on the rain-soaked runway.