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Aircraft Hydroplaning

Slippery When Wet

An unintentional stall close to the ground is one of the more dangerous situations a pilot can experience. Crosswind landings at mountain airports that have paved runways pose a special problem when the runway surface is wet because of hydroplaning. Hydroplaning is hazardous because it, like a stall, creates a loss of control.

Hydroplaning has traditionally been thought to pose a problem to larger aircraft, airliners and jets, however small aircraft are just as susceptible to the hydroplane condition.

By definition, a hydroplane is a motorboat that has been designed to skim long the surface of water. An aircraft tire on a wet runway hasn’t been designed to skim the surface, but it can.

Newton’s third law of motion states: “If body one exerts on body two a force, then body two exerts on body one a force that is equal in magnitude but exactly opposite in direction.” Substitute the tire for “force one” and a wet surface for “force two.” As the speed of the tire is increased the dynamic forces, that is, the relation between motion, energy and the forces affecting the motion, create a control problem in three ways.

Dynamic Hydroplaning

Dynamic hydroplaning is a condition where the tire is lifted completely above the surface of the runway. As little as one-tenth inch of water combined with the “NASA critical speed” of the tire is the causal factor.

Viscous Hydroplaning

Viscous hydroplaning can occur at slower speeds and rather than the water lifting the tire from the pavement, the tire slips on a thin film. This occurs on smooth runways.

Reverted Rubber (Steam) Hydroplaning

Encountering an emergency during takeoff or landing often causes the pilot to “lock” the brakes. If this occurs on a wet runway, the tire track area heats up due to friction causing some of the rubber to “revert back” to a gummy state, trapping water. The water turns to steam and steam pressure lifts the tire from the runway.


NASA has performed extensive tests and developed a formula that is applicable to all size aircraft. With sufficient water (0.1 inch), hydroplaning will occur at and above the speed predicted by this formula.

        NASA critical speed = 9 * (SQRT P)

The hydroplaning speed in knots (NASA critical speed) is equal to 9 times the square root of the tire pressure (pounds per square inch).

It is nearly impossible to land an airplane at a speed below the NASA critical speed, but pilot adhering to the following techniques can reduce the effects of hydroplaning.

  • Approach to land at the slowest airspeed consistent with safety, that is, the short-field landing technique.
  • Land firmly, rather than making the smooth, “greaser-type” landing.
  • Lower the nose wheel to the surface as soon as the main wheels are firmly on the surface.
  • Know the NASA critical speed and avoid heavy braking above this speed.
  • Retract the flaps immediately after landing to place more weight on the tires.
  • Divert to an alternate airport when conditions indicate hydroplaning potential on runways experiencing a strong crosswind.
















A slick runway surface producing hydroplaning is normally thought of as a surface with standing water associated with rain, but it can also be created by ice, snow, frost and dew.

(Keep this information in mind while driving to the airport, this formula will work for your vehicle too!)

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