Hydroplaning

Hydroplaning is loss of tyre grip when water separates the tyre from the runway. Three forms, each a different cause:

• Dynamic: standing water builds a wedge that lifts the tyre clear of the runway. Onset is near 9 × √(tyre pressure in psi) knots for a rolling (rotating) tyre (TC AIM AIR 1.6.6), so a higher tyre pressure raises the speed at which it starts.
• Viscous: a thin film on a smooth surface (rubber deposits, paint) stops the tyre gripping, and it can happen at low speed.
• Reverted-rubber: a locked, skidding tyre boils the trapped water to steam, which reverts the rubber and holds the tyre off the surface.

The non-rotating (locked) tyre hydroplanes even lower, near 7.7 × √(psi) (TC AIM AIR 1.6.6).

Note: the 9 × √(psi) onset speed is in the TC AIM (AIR 1.6.6); the dynamic / viscous / reverted-rubber three-form naming is the standard NASA/FAA breakdown, not spelled out in the TC AIM.

Trap: do not assume hydroplaning needs standing water and high speed. That is only the dynamic form; viscous hydroplaning needs just a thin film and can happen slowly.

Practice