The 2 formulas are 9xsquare root of the tire px for take off and 7.7xsquare root of the tire px for landing. As you can see the aquaplaning speed for landing is lower than for take off. The difference in speeds is due to the wheel either spinning down (rejected take off) or spinning up (landing).
When the tire hits the fluid, momentary fluid stagnation occurs when the tire tread pattern or the runway surface profile does not allow the fluid to escape. The fluid pressure build up is directly proportional to the fluid density and the ground speed squared. Therefore this speed can be accurately predicted and occurs when the stagnation pressure equals tire pressure. It also explains why a slippery surface and poor tread increases the likelihood of aquaplaning.
Hope this helps.
