Landing on wet runways a matter of the right technique

Landing on a runway recently soaked by a thunderstorm needs a modified technique.

Summer is on the way.

Landing on a wet runway when a thunderstorm has deposited prodigious amounts of water on the tarmac needs a modified technique to avoid problems. A pilot attempt at a “greaser”of a landing to impress the passengers can lead to problems on the landing roll.

All jet aircraft have anti-skid braking systems that rely on firm contact with the runway surface and wheel “spin-up” so the system can modulate the brake applications to avoid wheel skid.

It is necessary to have a firm landing to break through the surface film of water to ensure positive contact with the tyre rubber and the tarmac and ensure wheel spin-up, otherwise the tyres can slide over the surface of the water, skidding in a condition known as hydroplaning. Once started, hydroplaning can continue down to lower speeds resulting in a longer stopping distance, or worst-case, sliding off the runway.

A strong crosswind also can lead to loss of pilot control as the aircraft slides sideways off the runway. Hydroplaning onset speeds, static and dynamic, are a function of tyre pressure and are generally about 110 knots for landing and slightly higher for an aborted take-off where the wheels are rotating.

With touchdown speeds of about 130 knots there is a chance of hydroplaning if the landing is too smooth and exacerbated by worn tyres and pilots not deploying lift dump (spoilers/speedbrakes) to get all the weight on the wheels. Braking effectiveness relies on friction between the tyre and the tarmac and is increased with the downward force of weight.

The correct wet runway technique is a firm touchdown with immediate application of reverse thrust as soon as the nose wheels are lowered; then one firm and steady application of the rudder pedal toe brakes so the anti-skid system can operate properly.

Releasing and reapplying the brakes causes the system to work against the pilot, reducing the effectiveness. Blown tyres from locked wheels due to poor pilot technique were not uncommon in the days before anti-skid. An early version known as Maxaret did not have the locked wheel touchdown protection that modern anti-skid systems have.

A colleague demonstrating a Shorts 330 turboprop in Darwin years ago was too quick on the brakes before wheel spin-up and slid to a halt on the rims as the tyres blew out. A very short landing indeed!

Byron Bailey is an ex-RAAF fighter pilot and flew 777s as an airline captain