Forms of hydroplaning
Hydroplaning: water separates tyre from runway, grip lost. Three forms, different causes:
| Form | Water film | Speed | Condition |
|---|---|---|---|
| Dynamic | at least one-tenth of an inch deep | relatively high; onset near 9 × √(tyre pressure in psi) kt, rolling tyre (TC AIM AIR 1.6.6) |
- |
| Viscous | no more than one-thousandth of an inch deep suffices | much lower than dynamic | only smooth or smooth-acting surface, such as asphalt or touchdown area rubber-coated by earlier landings (AFH ch.9) |
| Reverted-rubber (steam) | only a thin film | can persist to groundspeeds of 20 kt or less | prolonged locked-wheel skid, heavy braking (AFH ch.9) |
- Dynamic: water wedge lifts tyre clear of runway. Higher tyre pressure raises onset speed (TC AIM AIR 1.6.6).
- Viscous: tyre rolls on top of film (AFH ch.9).
- Reverted-rubber: skid heat reverts rubber to uncured state, seals tyre footprint. Trapped water becomes steam, holds tyre off runway. Often follows dynamic hydroplaning with brakes locked. Remedy: release brakes, let wheels spin up, then brake moderately (AFH ch.9).
- Depends on water depth, tyre pressure, speed (TC AIM AIR 1.6.6).
Trap: use 9 for rolling tyre; 7.7 × √(psi) is locked (non-rotating) tyre, which hydroplanes at lower speed (TC AIM AIR 1.6.6).
References
- TC AIM AIR 1.6.6
- PHAK ch.11 (FAA-H-8083-25)
- AFH ch.9 (FAA-H-8083-3), Hydroplaning: dynamic, reverted-rubber, viscous