Aquaplaning is a common wet weather threat for all pilots.

Bad weather presents many issues that pilots may face upon take-off, landing, and especially during flight. A common threat is aquaplaning, which can happen with any vehicle and cause a complete loss of control after attempting to slow down on water-covered roads or runways. Let’s look at how this happens, the types of aquaplaning that can occur and how pilots can be equipped to handle it.

While it also relates to cars on roads, in aviation, aquaplaning is when an aircraft lands on a runway contaminated with water, slush, or wet snow, the Federal Aviation Administration (FAA) says.

While the incident can cause severe damage, it happens more often than one might think and isn’t as fatal as it sounds (as of yet). Most incidents have resulted in minor injuries and damage to the aircraft, such as the Qantas Flight 1 runway excursion, which led to over 30 passenger injuries. Most recently, the National Transportation Safety Board (NTSB) released a report in 2021 based on a Boeing 737-800 overrun on a Jacksonville Naval Air Station, Florida runway in 2019 caused by loss of braking due to aquaplaning, where one person was injured.

As an aircraft lands on the runway, a layer of water – a minimum of 3 mm of water depth – builds up beneath the tire in “increasing resistance to displacement by the pressure of the wheel,” SKYbrary explains. Further:

“Eventually, this results in the formation of a wedge between the runway and the tyre. This resistance to water displacement has a vertical component which progressively lifts the tyre and reduces the area in contact with the runway until the aircraft is completely water-borne. In this condition, the tyre is no longer capable of providing directional control or effective braking because the drag forces are so low.”

With water less than 3mm deep, aquaplaning is less likely to occur, with an exception in some cases. In Europe, the measurement helps determine in an investigation whether an aircraft excursion is caused by water build-up or a different reason.

There are three main types of aquaplaning: dynamic, reverted Rubber, and viscous. The FAA describes each of the types as quite similar.

Dynamic hydroplaning is when the aircraft is landing at “relatively” high speeds. It occurs when there is a film of water on the runway – at least one-tenth of an inch deep - and as the speed of the aircraft increases, the water builds up an increasing resistance to displacement and forms a wedge of water between the tire and runway.

According to the FAA, when the water pressure equals the aircraft’s weight, the tire slowly lifts off the surface and ceases rotating, resulting in losing control and braking. “Dynamic hydroplaning is often affected by tire inflation pressure,” the regulator said.

Reverted Rubber hydroplaning usually occurs during heavy braking, creating a “prolonged locked-wheel skid.” This type of aquaplaning is sneaky, as pilots often miss signs of it happening. It only requires a small amount of water, as the skid creates so much heat that the Rubber in contact with the runway will turn into its original “uncured” material as if it has melted.

The FAA describes the melted material as a seal between the tire and runway. Because the water cannot exit, the water continues to heat and then turns into steam. The FAA says:

“Reverted Rubber hydroplaning frequently follows dynamic hydroplaning, during which time the pilot may have the brakes locked in an attempt to slow the airplane. Eventually, the airplane slows enough to where the tires make contact with the runway surface and the airplane begins to skid.”

Lastly, viscous hydroplaning only requires the tiniest amount of water – as small as one-thousandth of an inch – to cause a runway excursion. Usually, it occurs at a far lower speed than dynamic hydroplaning and requires a smooth surface such as asphalt or an area covered with Rubber from past landings. The smoothness can replicate characteristics of wet ice. The FAA says viscous hydroplaning occurs when the tire cannot ride through the fluid; therefore, it rolls on top of the water.

The American regulator nods to how pilots can avoid hydroplaning, such as choosing runways with a grooved surface, touching down as slowly as possible, and using moderate braking. However, controlling a plane already experiencing aquaplaning requires the nose to be lifted, and aerodynamic drag used to decelerate enough for the brakes to work again. At any sign of a skid, the pilot should release the brake pressure and “allow the wheels to spin up,” the FAA says.

In the case of many hydroplaning incidents, there are many contributing factors, such as a lack of training, poor communication with air traffic controllers, and miscalculations regarding landing in wet weather conditions. The Jacksonville 2019 incident proved many reasons led to the incident. Most notably, the NTSB said former charter airline Miami Air International did not provide adequate guidance to pilots when landing during stormy conditions. The report cited:

“The flight crew did not follow procedures, including continuing an un-stabilised approach, landing the airplane at an excessive approach speed and delaying deployment of the speed brakes… However, investigators determined that even if none of those errors occurred, the airplane still would not have stopped on the un-grooved runway because the rainfall rate and runway characteristics contributed to water depths that caused the aircraft to hydroplane.”

Sources: FAA, NTSB report, SKYbrary